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Chillers are used in buildings to provide chilled water for use in air conditioning or other cooling applications. In some cases, waste heat from chillers is also used as a heat source for space heating or water heating in the building.

Click on a topic of interest below for more information about specific space cooling technologies.



Absorption Chillers

Use heat from gas-fired burners or waste heat from steam generating processes to produce chilled water.

General

The absorption cycle uses a heat-driven concentration difference to move refrigerant vapors (usually water) from the evaporator to the condenser. The high concentration side of the cycle absorbs refrigerant vapors (which, of course, dilutes that material). Heat is then used to drive off these refrigerant vapors thereby increasing the concentration again. Lithium bromide is the most common absorbent used in commercial cooling equipment, with water used as the refrigerant. Smaller absorption chillers sometimes use water as the absorbent and ammonia as the refrigerant. As you can probably guess, the absorption chiller must operate at very low pressures (about l/l00th of normal atmospheric pressure) for the water to vaporize at a cold enough temperature (e.g., at ~ 40°F) to produce 44°F chilled water.

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The simplified diagram here illustrates the overall flow path. Starting with the evaporator, water at about 40°F is evaporating off the chilled water tubes, thereby bringing the temperature down from the 54°F being returned from the air handlers to the required 44°F chilled water supply temperature. One ton of cooling evaporates about 12 pounds of water per hour in this step. This water vapor is absorbed by the concentrated lithium bromide solution due to its hygroscopic characteristics. The heat of vaporization and the heat of solution are removed using cooling water at this step. The solution is then pumped to the concentrator at a higher pressure where heat is applied (using steam or hot water) to drive off the water and thereby re-concentrate the lithium bromide. The water driven off by the heat input step is then condensed (using cooling tower water), collected, and then flashed to the required low temperature (40°F in our illustration) to complete the cycle. Since water is moving the heat from the evaporator to the condenser, it serves as the refrigerant in this cycle. There are also absorption chillers in use (e.g. in motor homes) that use ammonia as the refrigerant in the same cycle. The absorbent is the material that is used to maintain the concentration difference in the machine. Most commercial absorption chillers use lithium bromide. Lithium bromide has a very high affinity for water, is relatively inexpensive and non-toxic. However, it can be highly corrosive and disposal is closely controlled. Water of course is extremely low cost and safety simply isn't an issue.

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Absorption chillers are available in two types:

1. Single Effect (Stage) Units using low pressure (20 psig or less) as the driving force. These units typically have a COP of 0.7 and require about 18pph per ton of 9 psig steam at the generator flange (after control valve) at ARI standard rating conditions.

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2. Double Effect (2-Stage) Units are available as gas-fired (either direct gas firing, or hot exhaust gas from a gas-turbine or engine) or steam-driven with high pressure steam (40 to 140 psig). These units typically have a COP of 1.0 to 1.2. Steam driven units require about 9 to 10 pph per ton of 114 psig input steam at ARI standard rating conditions. Gas-fired units require an input of about 10,000 to 12,000 BTUH HHV per ton of cooling at ARI standard rating conditions. To achieve this improved performance they have a second generator in the cycle and require a higher temperature energy source.

Absorption chillers - maintenance considerations

Properly designed and installed absorption chillers can function without full time attendants. The machine can be started and brought on line with simple time clocks or energy management systems. Non-condensables are automatically purged and the operator can schedule normal routine maintenance. Obviously, local building codes may dictate that a full time operator is, or is not, required. This, in turn, is often a function of the size of the equipment, steam pressure, etc. Always consult local codes when considering these issues.

There are three primary maintenance areas: mechanical components, heat transfer components, and controls. The following segments discuss mechanical and heat transfer maintenance areas.

One manufacturer's absorption chillers has a single motor/multiple pump configuration for refrigerant and solution flow and a purge unit. Other manufacturers use individual hermetic solution and refrigerant pumps cooled and lubricated by the pumped solution. Another uses open motors with a shaft seal.

Pictured here are two hermetic, refrigerant cooled and lubricated pump assemblies. The hermetically sealed motor drives the solution and refrigerant pump impellers. In this multiple pump arrangement, motor coolant and lubrication is by the fluid being pumped. Hermetic pump designs eliminate the need for external shaft seals Ð a maintenance item and potential source of air leakage.

The life, performance, and cooling capacity of absorption equipment hinges on keeping heat transfer surfaces free of scale and sludge. Even a thin coating of scale can significantly reduce capacity. Therefore, cooling tower water chemistry is critical, and failure to properly treat this water could void manufacturer warranties.

Scale deposits are best removed chemically. Sludge is best removed mechanically, usually by removing the headers and loosening the deposits with a stiff bristle brush. The loosened material is then flushed from the tubes with clear water.

When the electric motor and pump bearings fail, one design permits replacement of pump parts without removing the lithium bromide solution from the machine. The first step is closing the hand valves in the lubrication circuit, disconnecting the electrical supply, and removing the motor. The pump shaft seal maintains machine vacuum. Major pump repairs are accommodated by charging the machine with nitrogen to atmospheric pressure. Once complete, the machine is evacuated, and pump parts removed and repaired or replaced. Other designs require a more complicated replacement procedure.

Pump maintenance begins with the magnetic strainer which must be cleaned 2 weeks after the initial startup and at the mid-point in the cooling season. Shaft seals should be examined for wear at three year intervals.

In the case of seasonal or prolonged shutdown, refrigerant may migrate from the evaporator to the absorption chiller causing a low refrigerant level in the evaporator pan and piping. Since refrigerant is used to lubricate pump and motor bearings, lubrication from an auxiliary source must be provided during the startup phase of operation. Once an operating charge of refrigerant has been recovered from the solution, the machine may be returned to normal operation.

This auxiliary circuit is usually established by connecting city water to the external connections of the pump lubrication piping. In all cases, follow the manufacturer's recommended procedures.

All absorption chillers must be purged of non-condensable gases to maintain performance. The three methods used are steam jet, solution jet (or "motorless purge"), or a vacuum pump, with the vacuum pump being by far the most common.

Non-condensable gases migrate to the area of lowest pressure in the absorption chiller (the evaporator) where a small portion of the vapor is extracted and condensed in the purge unit using cooling water. Non-condensable are then evacuated by the vacuum pump. In normal operation, the purge system should operate about one hour a week. The vacuum pump oil level should be observed, maintained, and changed as necessary. Oil purge pump motor bearings should be inspected and replaced, and the belt adjusted as needed. In addition, the vacuum pump should be flooded with oil during seasonal shutdown to prevent internal corrosion.

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Purging of non-condensables can be accomplished using a "motorless purge" as shown here. Where motorless purging is used, an optional vacuum pump can also be used for evacuation.

In all cases, the operator should log purge operation and monitor purge operation trends. Increasing purge operation signals increasing in-leakage of air and moisture.


Applications

Single stage steam absorption chillers

Provide chilled water for cooling when low pressure steam, cooling tower (or other water for heat rejection), and electric power is available.

Two stage absorption chillers

Provide chilled water for cooling when high pressure steam, high temperature hot water (HTHW) or natural gas, as well as electric power and cooling tower (or other water for heat rejection) is available.

Waste heat fired absorption chillers

Provide chilled water for cooling when clean, hot exhaust gas, cooling tower (or other water for heat rejection), and electric power is available.

Best applications

Single stage steam absorption chillers

When steam in the 12 to 20 psig range from a process or other steam use is available at little or no cost (i.e. steam would otherwise be wasted).

Two stage absorption chillers

When steam in the 40 to 140 psig range from a process or other steam use is available at little or no cost (i.e. steam would otherwise be wasted), When natural gas is available at low cost relative to the cost of electric power,

When the heating load can not be readily served by an existing boiler and it can be served from this chiller/heater, thus avoiding adding a boiler or where space is not available for a boiler.

When adequate electric power is not readily available for added and needed cooling capacity,

When emergency cooling capacity is needed and stand-by generation capacity is not available to operate electric cooling. (Consider adding emergency generation capacity, which may be lower in cost than absorption cooling capacity).

Waste heat fired absorption chillers

Where exhaust from a gas turbine provides cooling for the intake air to improve turbine performance in hot weather,

Where cooling is required and clean exhaust gas is available, emitted from an industrial process such as those related to printing, drying or baking.

Possible applications

Single stage steam absorption chillers

When steam in the 12 to 20 psig range from a process or other steam use is available at a reasonable cost or where boilers must be operated for other reasons and the user is looking for other steam uses to adequately load the boiler.

Two stage absorption chillers

When steam in the 40 to 140 psig range from a process or other steam use is available at a reasonable cost or where boilers must be operated for other reasons and the user is looking for other steam uses to adequately load the boiler,

Replacement for existing inefficient single stage steam chiller without an electrical service upgrade.

Waste heat fired absorption chillers

Where clean exhaust gas is available and there are cooling requirements.

Waste heat fired absorption chillers

skilled operating personnel will not on duty during system operation,

operations are planned to use absorption chiller as a peak shaving unit. Absorption chillers require added to time and effort to bring on- and take off-line. Operators tend to end up using absorption as a base chiller and peak with the electric chiller, thereby defeating the purpose, and actually adding to, rather than saving, operating cost.

Extended operation at 30% and less of design capacity is likely.

Technology types (resource)

Two stage absorption chillers

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The energy efficiency of absorption can be improved by recovering some of the heat normally rejected to the cooling tower circuit. A two-stage or two-effect absorption chiller accomplishes this by taking vapors driven off by heating the first stage concentrator (or generator) to drive off more water in a second stage. Many absorption chiller manufacturers offer this higher efficiency alternative.

Notice that two separate shells are used. The smaller is the first stage concentrator. The second shell is essentially the single stage absorption chiller from before, containing the concentrator, condenser, evaporator, and absorption chiller. The temperatures, pressures, and solution concentrations within the larger shell are similar to the single-stage absorption chiller as well.

Steam at pressures typically in the l25 - 150 psig range is brought into the stainless steel tubes of the first stage concentrator causing the solution there to boil. The pressure at which boiling occurs and the pressure of the released refrigerant vapor is approximately 5 psig (20 psia). The partially concentrated solution from this first stage flows through the high temperature heat exchanger where it is cooled by the lower temperature dilute solution returning from the concentrator. This concentrate then passes into the lower pressure second stage concentrator where the vapors from the first stage take it to the final desired concentration levels. This second stage operates at a pressure of 0.1 atmosphere (1.5 psia).

The reuse of the vapors from the first stage generator makes this machine more efficient than single stage absorption chillers, typically by about 30%. Two-stage absorption chillers are typically driven by high-pressure (60 to 130 psig) steam, direct-fired with natural gas or #2 fuel oil, or using hot exhaust gas from combustion engines.

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Steam-fired 2-stage absorption chillers

Steam at pressures typically in the l25 - 150 psig range is brought into the stainless steel tubes of the first stage concentrator causing the solution there to boil. The pressure at which boiling occurs and the pressure of the released refrigerant vapor is approximately 5 psig (20 psia). The partially concentrated solution from this first stage flows through the high temperature heat exchanger where it is cooled by the lower temperature dilute solution returning from the concentrator. This concentrate then passes into the lower pressure second stage concentrator where the vapors from the first stage take it to the final desired concentration levels. This second stage operates at a pressure of 0.1 atmosphere (1.5 psia).

The reuse of the vapors from the first stage generator makes this machine more efficient than single stage absorption chillers, typically by about 30%.

Direct-fired absorption chillers

Direct-fired absorption chillers utilize a burner as the heat input for the absorption cooling cycle. Most operate either on natural gas or No. 2 fuel oil. Since the heat input is at a very high temperature, they achieve a very high efficiency for the absorption cycle...something approaching 12,000 Btu of fuel input for each ton hour of cooling output. The absorption cycle itself is virtually identical to that of the two-stage steam absorption chillers. However, unlike most steam absorption chillers, the direct-fired absorption chiller lends itself fairly readily to "chiller-heater" applications where both cooling and heating are achieved in the same unit. This can result in a smaller footprint for the boiler room in some situations.

Advantages

Where a boiler can be eliminated by the dual heating and cooling capability of this machine, the cost and space savings can be a significant. In addition, steam is not required, which can be important in situations where local codes require licensed boiler operators for steam-driven units but permit unmanned operation of direct-fired absorption chillers.

Disadvantages

Direct-fired absorption chillers require a stack to vent combustion products. This is not necessary in a steam-fired unit. In addition, the first cost of direct-fired units are higher than steam driven units. Maintenance costs on the heat rejection circuit tend to be higher due to more rapid scaling. Also be careful to check warranted life of absorption chiller heat transfer surfaces (especially the generator section) and the refrigerant and solution pumps. All absorption chillers use electric power to operate these pumps, the condenser water pumps and cooling tower fans. They also use more water as they must reject more heat and require larger cooling towers.

Absorption chillers are more difficult than electric chillers to put on-line (start up) and to take off-line (shut down) as they require a dilution cycle. All of these issues should be addressed in discussions with manufacturers, designers and mechanical contractors.

Waste heat fired absorption chillers

Most absorption chillers use either steam or fuel (natural gas, propane) for heat input. But, waste heat from process, reciprocating engine, gas turbine, or a cogeneration system can also be used in the absorption process. The exhaust should have a minimum temperature of about 550 F and a maximum of 1,500 F. The most common application is using the exhaust from a gas turbine to provide cooling for the intake air or other cooling requirements. The available cooling is a function of the exhaust gas temperature and mass flow rate, using this formula:

Chilling capacity in tons = m x (Tg - 375) / 40,950

Where m = mass flow rate in pound per hour

Tg = exhaust gas inlet temp (F) to absorption chiller

40,950 = conversion factor

More detail

Waste steam from a cogeneration system obviously produces the same level of cooling as boiler generated steam, Low pressure waste steam sources (say 14 psig) typically require 18-20 pounds of steam per hour to produce one ton of cooling in a single-stage absorption chiller. That performance improves to 10-12 pounds per ton-hour of steam when steam pressures are in the 50 to 130 psig range and used in a 2-stage (double effect) absorption chiller.

Steam absorption chillers are nominally rated as follows:

  • Single stage: 9 psig at generator flange
  • Two stage: 114 psig steam input pressure.

Capacity ratings are decreased as steam pressure drops below nominal. For example, a nominal 100-ton unit's capacity will drop to 84 tons with 78.5 psig steam.

Direct-fired absorption chillers can often be modified to accept hot air or exhaust from a gas turbine or engine. Performance is almost totally dependent upon air temperature, For example, waste heat air temperatures °F or higher offer performance similar to direct-fired absorption chillers where every 13,000 Btu of heat recovered produces one ton of cooling. When calculating heat recovery, remember to assume waste heat leaving the absorption chiller at 375° to 400°F (this means the absorption chiller will not reclaim all of the waste heat potential).

For exhaust gas heat recovery

Chilling capacity (tons) = m x (Tg - 375)

40,950

Heating capacity (BTUH) = m x (Tg - 375) x 0.257

where m = exhaust gas flow rate in pounds per hour

Tg = exhaust gas inlet temperature in °F

40,950 = cooling constant representing average gas specific heat, interconnect efficiency, cooling COP and the conversion from BTUH to tons

0.257 = heating constant representing average gas specific heat and the interconnect efficiency

375 = minimum temperature of exhaust gas leaving chiller in °F.


Centrifugal & Screw Packaged Chillers

Packaged for easy installation, these units are used in larger buildings. They are the most efficient and offer the lowest weight, height and footprint of any chiller alternative.

General

Centrifugal, and to a lesser extent screw, packaged chillers are the heart of most central systems for large buildings. They consist of the centrifugal or screw compressor-motor assembly, water-cooled condenser, insulated liquid cooler, expansion device, interconnecting refrigerant piping, lube system, oil and refrigerant charge, control panel and wiring, auxiliaries, and in some cases the compressor motor-starter. They are made in both hermetic and open types, and with single- and multi-stage centrifugal designs. They are manufactured, factory assembled and tested, charged, and shipped in one assembly up to about 2,000 tons capacity; in large sizes they are factory disassemble in major pieces for shipment and installation. Installation consists of piping supply and return chilled water or brine piping, and cooling water piping, power wiring and interconnection of external controls, evacuation and charging when necessary, check-out and startup.

NOTE: Screw compressors are also sometimes referred to as ahelical rotary compressors.

Advantages

  • Factory packaged for ease of proper installation
  • Most efficient chilling package - low kW per ton (centrifugals at 0.50 and less available, with screws at somewhat higher kW per ton)
  • Several major reliable suppliers, each with a service network of trained technicians
  • Available from 100 to 10,000 tons capacity in a single centrifugal chiller, with screws available in a lower tonnage range - check suppliers)
  • Lowest weight, height and footprint of any alternative
  • Use environmentally acceptable refrigerants
  • Have excellent and step-less part load characteristics
  • Are available in some sizes in dual compressor models for even more efficient part load operation
  • Chillers are relatively easy to operate with their modern controls and designs

Disadvantages

  • More costly in smaller sizes than other types of chiller packages
  • Centrifugal chillers are available only in water-cooled models
  • Screw compressor chillers are somewhat noisier than other designs
  • Screw compressor chillers are somewhat less efficient than centrifugals
  • Applications

    Centrifugal and screw packaged chillers are typically applied in single and multiple units to provide chilled water for air conditioning large buildings and complexes, and in district cooling systems. They are also used in heat pump form for both heating and cooling. They are also used to chill brine in industrial processes.

    Best applications

    Centrifugal chillers are usually the best selection among alternatives when used to provide chilled water for cooling large buildings with automated operation.

    Technology types (resource)

    See also:

    Efficiency

    Centrifugal chillers are the most efficient chilling packages available. Recent design improvements result in a low kW per ton (centrifugals are available at 0.50 and less kW/ton, with screws at somewhat higher kW per ton). Higher kW per ton can also be supplied at lower first costs; these may or may not be prudent depending on the present and anticipated cost of power (both demand and energy).

    Contact us for a detailed list of manufacturers for this equipment.


    Reciprocating & Scroll Packaged Chillers

    Packaged for easy installation, these chiller units are typically used in smaller buildings and offer lower installation costs.

    General

    Reciprocating, and to a lesser extent scroll, packaged chillers are the heart of most central systems for medium sized buildings. They consist of one or more reciprocating or scroll compressor-motor assembly, air- or water-cooled condenser (and condenser air fan(s)), insulated liquid cooler, expansion device, interconnecting refrigerant piping, oil and refrigerant charge, control panel and wiring, auxiliaries, and the compressor motor-starter. They are made in both full- and semi-hermetic and open types. They are manufactured, factory assembled and tested, charged, and shipped in one assembly up to about 2,00 tons capacity. Installation consists of piping supply and return chilled water piping, (and cooling water piping where applicable,) power wiring and interconnection of external controls, evacuation and charging when necessary, check-out and startup. Units are also available without any condenser for field piping to a separate remote air-cooled or evaporative condenser.

    Advantages

    • Factory packaged for ease of proper installation
    • Many reliable suppliers, most with a service network of trained technicians or through factory approved service providers
    • Reciprocating models available from many manufacturers in capacities up to 200 tons and larger in incremental steps (i.e. 20, 25, 30, etc)
    • Scroll chillers are available from a lesser number of manufacturers and more limited models (20 to 60 tons - check suppliers)
    • Scroll chillers have improved part load efficiencies
    • Use environmentally acceptable refrigerants
    • Various condensing options available, including air-cooled and for low ambient operation
    • Chillers are relatively easy to operate with their modern controls and designs

    Disadvantages

    • Reciprocating models: Part load capacity is stepped - cylinder unloading, compressor on/off of multiple compressor units
    • Central plant systems tend to be more costly than unitary systems

    Links to more detail

    Applications

    Reciprocating and scroll packaged chillers are typically applied in single and multiple units to provide chilled water for air conditioning small to medium sized buildings using central system designs.

    Best applications

    High quality installations requiring central chilled/hot water systems to provide temperature and humidity control of multiple spaces.

    Retrofit applications

    Many models will fit through a 30 inch door for ease of installation at minimum cost of structural modifications.

    Technology types (resource)

    Reciprocating compressor packages have been the mainstay of this segment, and many advances and improvements have been made over the years. They are in wide-spread use and trained service technicians are available almost everywhere.

    Scroll compressor packages are the latest advancement in positive displacement compressors and indications are they may offer better reliability and improved efficiency. The network of trained service technicians is in the process of development and may not be available in all locations.

    Efficiency

    Older water cooled chillers are in the 0.82 to 1.0 kW per ton range, while newer high efficiency models range from 0.78 to 0.85 kW per ton at ARI conditions.

    Contact us for a detailed list of manufacturers for this equipment.


    Natural Gas - Engine Driven Chillers

    These are similar to their electric counterparts but use compressors driven by natural gas engines.

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    General

    While the majority of the packaged chillers sold and installed are electric drive, efforts by the gas industry have resulted in several manufacturers offering packaged natural gas engine driven chillers using reciprocating, screw and centrifugal chillers. These chillers are essentially the same as electric driven counterparts except open drive compressors are used. These in turn are matched with natural gas engines and often optional heat recovery heat exchangers. Most chillers use R-22 refrigerant.

    Advantages

    • Modulation of both engine speed and compressor unloading provide good part load operation
    • Can reduce demand charges if properly operated
    • Heat recovery options for producing hot water are available
    • Both water- and air-cooled models are available

    Disadvantages

    • Require high electric parasitics to operate (pumps - chilled water, tower, lube, etc. and fans)
    • Require periodic and added maintenance time and cost, with engine maintenance performed by a different trade that normally services chillers
    • Requires added water use due to higher heat rejection; may require larger tower and pumps Higher weight and space requirements
    • Emissions may require permitting and emission reduction controls
    • While lean-burn low-emission engines are available, they tend to have higher emissions at part load - a condition at which most chillers operate a large portion of the time
    • Engines require major overhaul or rebuild after a period of time
    • When heat recovery is used, provision must be made to reject unwanted heat whenever it can not be put to use
    • Engine noise control must be considered in design and added cost sound enclosure may be required
    • Units are more expensive than conventional electric chillers
    • The engine is only operated when cooling is needed.

    Applications

    Can be applied almost anywhere a comparable electric chiller is used, if space and a supply of low-cost gas is available and added weight can be handled by the structure.

    Best applications

  • Where insufficient power is available to operate an all-electric chiller.
  • Where demand charges are high and cost of gas is low
  • Technology types (resource)

    There are two philosophies in the application of engines to chillers. The first is to connect the engine and compressor, directly or through gearing. This is what is described above, and what usually comes to mind when the phrase "engine driven chiller" is used.

    The second questions why an engine is installed and only used when cooling is required, which is usually during only several months a year and then at partial load most of the time. Two alternatives can be considered. One connects both a generator and the compressor to an engine; this tends to be both more expensive to purchase, and complicated to install and operate.

    The second approach is to install a conventional high efficiency electric chiller and an engine-driven generator sufficient in size to power the chiller. The power generated is used to drive the chiller and its auxiliaries. When all the output power is not required, which is during most of the year, the excess power is used for other purposes in the building. This makes sense when the customer wishes to diversify fuel use.

    Another consideration is that most users do not realize the commitment they are making when they install gas engine drives. They take the minimum maintenance of electric motors for granted and tend to expect the same of engines. This is not so.

    Internal combustion engines require periodic scheduled shutdown for routine maintenance (lube oil and spark-plug changes, etc) , plus top and major overhauls at various points in their lifetime. These "time between overhaul" periods can range from 3,600 hours for light high-speed engines used in small gensets to 15,000 - 20,000 or higher run-hours for heavier slow speed industrial grade engines. Set-asides of downtime and dollars must be made for these procedures

    Efficiency

    High efficiency gas engine-driven chillers have COP's at full load of 1.2 to 1.7 with part load up to 2.2. Typical integrated part load values (IPLV) at ARI conditions range from 1.6 to 2.0. Water-cooled models with engine heat recovery usefully used, can gain an additional 0.5 COP.

    Contact us for a detailed list of manufacturers for this equipment.


    Centrifugal Compressors

    Typically found in large chiller units, these are the most efficient systems and use one or more rotating impellers to compress refrigerant.

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    General

    Centrifugal compressors use one or more rotating impeller to increase the refrigerant vapor pressure from the chiller evaporator enough to make it condense in the condenser. Unlike the positive displacement, reciprocating, scroll or screw compressors, the centrifugal compressor uses the combination of rotational speed (RPM), and tip speed to produce this pressure difference. The refrigerant vapors from the chiller evaporator are commonly pre-rotated using variable inlet guide vanes. The consequent swirling action provides extended part-load capacity and improved efficiency. The vapors then enter the centrifugal compressor along the axis of rotation. The vapor passageways in the centrifugal compressor are bounded by vanes extending form the compressor hub, which may be shrouded for flow-path efficiency. The combination of rotational speed and wheel diameter combine to create the tip speed necessary to accelerate the refrigerant vapor to the high pressure discharge where they move on to the chiller condenser. Due to their very high vapor-flow capacity characteristics, centrifugal compressors dominate the 200 ton and larger chiller market, where they are the least costly and most efficient cooling compressor design. Centrifugals are most commonly driven by electric motors, but can also be driven by steam turbines and gas engines.

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    Depending on the manufacturer's design, centrifugal compressors used in water chiller packages may be 1-, 2-, or 3-stages and use a semi-hermetic motor or an open motor with shaft seal.

    Advantages

    Due to their very high vapor-flow capacity characteristics, centrifugal compressors dominate the 200 ton and larger chiller market, where they are the least costly and most efficient cooling compressor design.

    More detail

    Packaged water cooled centrifugal compressors are available in sizes ranging from 85 tons to over 5,000 tons. Larger sizes, typically those 1,200 to 1,500 tons and larger are shipped in sub-assemblies. Smaller sizes are shipped as a factory-assembled package. While some smaller air-cooled centrifugal models are manufactured, they are largely exported to the Middle East and other arid areas where water is simply not available for HVAC condensing use, even in cooling towers.

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    The centrifugal compressors mentioned here will be using HCFC-123, HCFC-22 and HFC-134a. This usually calls for semi-hermetic designs, with single or multi-stage impellers. Two manufacturers (Carrier and McQuay) offer semi-hermetic gear driven models. Trane offers multi-stage direct drive semi-hermetic units. York offers an integrated open-drive geared design.

    Chillers using ammonia as the refrigerant are not generally available with centrifugal compressors. Only open drive screw or reciprocating compressors are compatible with ammonia, largely because of its corrosive characteristics and reactions with copper.

    The selection of single stage, multi-stage, open or hermetic designs is largely a function of individual manufacturer preference and the application. For example, centrifugal compressors are limited in their compression ratio per impeller. Therefore, applications calling for high temperature lifts (such as with ice thermal storage) may require multi-stage designs.

    Power requirements for centrifugal chillers are the lowest of all chiller types currently available, and efficiencies have been improving even further over the years as a result of improved impeller designs, better unit configurations, enhanced heat transfer surfaces, and the increased utility emphasis on reducing energy requirements.

    At ARI standard rating conditions centrifugal chiller's performance at full design capacity ranges from 0.53 kW per ton or lower to 0.68 kW per ton. This performance includes the semi-hermetic refrigerant cooled or open type compressor motors.

    Open drive chiller power requirements are sometimes rated in shaft brake horsepower (bhp). To convert from bhp to electric input in kW, the efficiency of the motor must be considered (which is usually between 90 and 95 percent for centrifugal machines). For example, a rating of 1,000 bhp at 93 % motor efficiency would translate to 802 kilowatt input.

    (1,000bhp x 0.746 kW/bhp) = 80.2 kW input

    93% Motor efficiency

    Centrifugals chillers 200 tons and larger cost less to install than reciprocating chillers (available up to the 175 to 200 ton range) and the same or slightly less than screw chillers in most all sizes. Centrifugals offer the advantages of high efficiency, infinitely variable capacity control (down to about 10 percent of full load), they're lighter (which reduces floor loadings) and they take up much less space for a given tonnage.

    First cost of centrifugal chiller packages generally start higher than recips under 200 tons, and then cost less in the larger sizes. More definitive costs are shown in the Compare segment.


    Screw Compressors

    Typically found in mid-size chiller units, these highly efficient systems use one or two rotating screws to compress refrigerant.

    General

    Helical rotary (or screw) compressors are positive displacement machines. Two types are used - single-screw and twin-screw. A twin-screw compressor consists of accurately matched rotors (one male and one female) that mesh closely when rotating within a close tolerance common housing. One rotor is driven while the other turns in a counter-rotating motion.

    A single-screw compressor uses a single main screw rotor meshing with two gate rotors with matching teeth. The main screw is driven by the prime mover, typically an electric motor. The gate rotors may be metal or a composite material. The screw-like grooves gather vapors from the intake port, trap them in the pockets between the grooves and compressor housing, and force them to the discharge port along the meshing point path. This action raises the trapped gas pressure to the discharge pressure. If the power input is adequate and pressure differential between outlet and inlet pressures is within the design range of the machine, the screw compressor delivers the appropriate refrigerant gas volume.

    Notice that the refrigerant gas enters and exits the compressor through ports; not valves like reciprocating compressors. Compressors of this type are called ported compressors for this reason. The mating rotors are rotating at such close tolerances, they require cooling and lubrication. This may be provided by forcing oil into the compressor at strategic points. The oil also acts as a seal for rotor-to-rotor and rotor-to-housing clearances.

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    The oil is entrained by the flowing refrigerant gas, leaves the compressor, and is recovered by an oil separator for reuse (after cooling and filtering). Since the oil sump is on the high pressure side of the system, a mechanical pump is not required for oil circulation. The compressive action of the screw itself provide the necessary pressure differential.

    In other designs, subcooled liquid refrigerant injection (instead of oil) cools and seals the compressor. The use of liquid refrigerant eliminates oil management problems as there are no oil separators or oil recovery systems. The system is sealed, cooled and lubricated with liquid refrigerant which also attenuates the noise. Capacity is controlled with two slide valves.

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    Since the screw compressor is most often driven by a constant speed electric motor and the screw compressor is a positive displacement machine, the natural tendency is to move a fixed volume of refrigerant gas. This would make refrigeration capacity control difficult. The design uses a slide valve that opens to vent some gas back to the suction port, reducing both the net gas flow and power input.

    Several manufacturers offer packaged water chillers using helical rotary or "screw" compressors. Water-cooled units range in size from 50 tons to over 1200 tons. They normally use HCFC-22 and HFC134a as refrigerants in space cooling designs and ammonia in process refrigeration (particularly food processing). In the smaller sizes, they compete with reciprocating chillers. In larger sizes they compete with centrifugals. Screw compressors usually employ hermetic or semi-hermetic designs for higher efficiency, minimum leakage, ease of service, and volume production reasons.

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    Air- and evaporatively-cooled models can be used from about 60 to 350 tons, and can use open-drives. Chillers using ammonia always use open type compressors, typically with direct-coupled electric motors. The selection of open or hermetic design depends on the application, refrigerant, and the manufacturer.

    Technology types (resource)

    Two types are used - single-screw and twin-screw. A twin-screw compressor consists of accurately matched rotors (one male and one female) that mesh closely when rotating within a close tolerance common housing. One rotor is driven while the other turns in a counter-rotating motion.

    A single-screw compressor uses a single main screw rotor meshing with two gate rotors with matching teeth. The main screw is driven by the prime mover, typically an electric motor. The gate rotors may be metal or a composite material. The screw-like grooves gather vapors from the intake port, trap them in the pockets between the grooves and compressor housing, and force them to the discharge port along the meshing point path. This action raises the trapped gas pressure to the discharge pressure. If the power input is adequate and pressure differential between outlet and inlet pressures is within the design range of the machine, the screw compressor delivers the appropriate refrigerant gas volume.

    Contact us for a detailed list of manufacturers for this equipment.


    Reciprocating Compressors

    Typically found in smaller chiller units, these use pistons and intake and exhaust valves to compress refrigerant. Only refrigerants that operate as a vapor can be used.

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    Most cooling systems in use today rely on reciprocating piston-type compressors. Reciprocating compressors are manufactured in three types:

    1. Hermetic - compressor-motor assembly contained in a welded steel case, typically used in household refrigerators, residential air conditioners, smaller commercial air conditioning and refrigeration units.
    2. Semi-hermetic - compressor-motor assembly contained in a casting with no penetration by a rotating shaft and with gasketed cover plates for access to key parts such as valves and connecting rods.
    3. Open - compressor only with shaft seal and external shaft for coupling connection to belt - or direct-drive using as electric motor or natural gas engine. These are largely used for ammonia refrigeration applications as hermetic designs cannot be used with ammonia refrigerant, and for engine-driven units.

    As the piston nears the bottom of its stroke within the cylinder, the intake valve opens and the refrigerant vapor enters. As the piston rises, the increased pressure closes the intake valve. Then as the piston nears the top of its stroke, the exhaust valve opens permitting the vapor at the higher pressure to exit. Reciprocating compressor capacity is a function of the bore and stroke of the piston-cylinder configuration as well as the speed of the machine, and the clearance tolerances. Compressor capacity is also related to the compression ratio.

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    The mechanical design is rugged and reliable but has one significant limitation. Reciprocating compressors are designed to handle vapors, not liquids. When liquid enters the cylinder on the intake stroke, it tends to damage the valves on the compression stroke and possibly the compressor itself. This is why chillers incorporate liquid-to-suction heat exchangers, which assure some level of vapor superheat at the compressor suction. Capacity is controlled by multiple staging of smaller compressors or in large multiple cylinder reciprocating compressors by unloading banks of cylinders on the compressor. This tends to make the machine most efficient at full load. Therefore, for maximum efficiency recips should generally be operated at full load. This is the reason small compressors are cycled on and off in most residential and small commercial applications.

    The mechanical design is rugged and reliable but has one significant limitation. Reciprocating compressors are designed to handle vapors, not liquids. When liquid enters the cylinder on the intake stroke, it tends to damage the valves on the compression stroke and possibly the compressor itself. This is why chillers incorporate liquid-to-suction heat exchangers, which assure some level of vapor superheat at the compressor suction.

    More Detail

    Due to better valve designs and configurations that reduce pressure losses, power requirements for reciprocating chillers have been improving over the years. Overall mechanical and compression efficiencies vary with the compression ratio, but are generally in the 72 to 78% range including the hermetic-type refrigerant-cooled 1,750 rpm motor. Compression ratio is computed by dividing the absolute discharge pressure by the suction pressure both measured in psia.

    At ARI Standard rating conditions (44°F leaving chilled water, 85°F entering condenser water), typical chillers operate around 40°F evaporating and 100°F condensing temperatures equivalent to pressures. A modern reciprocating compressor has an energy efficiency ratio (EER) of about 15, equal to 0.79 kW per ton. However, in air-cooled conditions the condensing pressure is likely to run up to a 130°F temperature corresponding to pressure, with EERs ranging from about 10.4 up to 11.3, which equate to 1.15 to 1.06 kW per ton.

    Assembled into chiller packages in the 20 to 200-plus ton capacities, air-cooled units will typically have EERs ranging from 9.0 to 10.9, equal to 1.33 to 1.10 kW per ton with an average of about 1.22 kW per ton. Similar water-cooled chiller packages will have EERs ranging from 13.1 to as high as 15.8, which equates to 0.92 to 0.76 kW per ton with an average of about 0.82 kW per ton.

    Manufacturers continue to develop more efficient models. In some cases, scroll compressors are being used, in place of reciprocating.

    While they are the least efficient of the chiller package options, reciprocating or scroll compressor chillers have a definite first cost advantage in the smaller chiller sizes. The first cost of reciprocating chiller packages is the lowest of the various electric chiller options, certainly when expressed in $ per ton. The compressors are competitively priced since they are used in many different chiller models. Plus, many more reciprocating chillers are produced than larger centrifugal and screw type chillers. These economies of scale result in a lower unit cost, especially for models up to about 200 tons.

    Compare - Installed Costs - Chillers

    For example, an air-cooled chiller serving a hospital operating room suite that operates year-round could well have a lower annual electric cost than a comparable water-cooled unit, due to the large number of operating hours the unit will be operating at part-load and low-ambient temperature conditions. Only a careful energy use analysis of each application performed by a qualified professional can identify the most economical equipment choice.

    Maintenance costs must also be factored in. Here are some typical mid-1995 $ per ton annual values.

    Chiller Type 20 Tons 50 Tons 75 Tons 100 Tons 150 Tons 200 Tons
    Water Cooled $79 $67 $58 $51 $40 $35
    Air Cooled $70 $50 $45 $43 $35 $31

    If the chiller is driven by a natural gas engine, the added maintenance costs of the engine must also be included. Typically this amounts to about $0.012 per ton per operating hour.

    Reciprocating chiller emissions fall into two major categories: direct (or on-site), and indirect (or emissions resulting from the production of the energy used to operate the equipment).

    Direct on-site emissions are confined to the release of refrigerant due to leaks or servicing. Federal law now mandates no intentional release. It is the responsibility of the user and service agency to minimize leaks and service release. Good preventive maintenance practices are imperative. Other factors affecting emissions include chiller age, application (whether it's a single package or split system), compressor type (open compressors with shaft seals tend to leak more than hermetic designs).

    A typical semi-hermetic type chiller might lose about 3 to 5 percent of its charge annually. With the refrigerant charge running about 3 pounds per ton, the emission of refrigerant might total about 0.12 pounds per ton per year. An open chiller might lose 5 to 7 percent, and thus emit about 0.18 pounds per ton-year. To allow for less than ideal conditions, a conservative estimate of emissions might be 0.25 pounds per ton-year.

    Natural Gas engine-driven reciprocating chillers must use open-type compressors. In addition to the same refrigerant emissions as an electric chiller, they also produce emissions from the combustion of the natural gas. Also, the leakage of natural gas into the atmosphere although small, is believed to contribute comparable greenhouse gases as refrigerant leakage.

    These emissions can be estimated, based on the annual gas consumption. Typical gas engine driven chillers use about 9,300 Btu per ton-hour of natural gas (on a HHV basis). Using the annual ton-hours of cooling, the emissions of CO2 and the criteria gases can be estimated using these relative values of pounds per million Btu of fuel burned. The emissions of all gases other than NOx are relatively constant throughout the loading range. NOx emissions will vary considerably, depending on the annual load profile.

    On-site emissions in pounds per million Btu of Natural Gas burned
    CO2 CO NOx SOx VCC Particulates*
    118 20% 44% 0 .31 .00%

    *Particulates are 10 microns or less. Volatile organic compounds (VOC) includes hydrocarbons (HC).

    While so-called "lean-burn engines" emit less NOX than conventional engines at full load, they emit more at part load conditions. Since chillers operate largely at part load, the added expense of a lean-burn engine is usually not justifiable.

    Indirect emissions occur at the power plants generating the electricity used to power chillers. Remember that comparing different chillers (for example, electric versus gas) must include the effect of the chiller and system auxiliary energy consumption - not just the chiller's power use. These emissions can be estimated from the annual power consumption in kWh and the local electric utility's emission data.

    Most utilities know their typical emissions of the various gases andparticulates on a "per kWh" basis.


    Scroll Compressors

    This recent design uses one stationary and one orbiting scroll to compress refrigerant. Being more efficient, these will eventually replace most reciprocating compressors.

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    The scroll compressor uses one stationary and one orbiting scroll to compress refrigerant gas vapors from the evaporator to the condenser of the refrigerant path. The upper scroll is stationary and contains the refrigerant gas discharge port. The lower scroll is driven by an electric motor shaft assembly imparting an eccentric or orbiting motion to the driven scroll. That is, the rotation of the motor shaft causes the scroll to orbit - not rotate - about the shaft center.

    This orbiting motion gathers refrigerant vapors at the perimeter, pockets the refrigerant gas, and compresses it as the orbiting proceeds. The trapped pocket works progressively toward the center of the stationary scroll and leaves through the discharge port. Study this time lapse series carefully to see how the trapped gases are progressively compressed as they proceed toward the discharge port.

    Scroll compressors are a relatively recent compressor development and will eventually replace reciprocating compressors in many cooling system applications, where they often achieve higher efficiency and better part-load performance and operating characteristics.

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    Advantages

    Scroll compressors are a relatively recent compressor development and will eventually replace reciprocating compressors in many cooling system applications, where they often achieve higher efficiency and better part-load performance and operating characteristics.


    Mechanical Drives

    A variety of electric motor, gas turbine, reciprocating engine, and steam turbine alternatives are available to drive chiller compressors.

    Chiller compressors can be driven by electric motors, reciprocating engines, gas turbines, or steam turbines. The selection of alternative drive technologies rests primarily on the issues of first cost and operating cost, as well as any fuel diversity and power reliability criteria. While there are other issues involved in the selection process, including CFC phaseout and other refrigerant-related issues, the selection between the alternatives just mentioned will probably not be driven by CFCs. In other words, a refrigerant that might be applicable for a chiller driven by a reciprocating engine would also work for an electric motor drive. A discussion of these criteria can be found elsewhere in this digital reference library.

    While mechanical drives other than electric motors are also discussed, the primary alternatives presented will be reciprocating engines in the 100-500 ton range and steam turbines which are typically much larger.

    Gas turbine-driven chillers are seldom seriously considered for three reasons:

  • The limited number of gas turbine sizes available
  • Their economic reliance on heat recovery and
  • Their relatively poor on-peak performance during hot weather.
  • Technology types (resource)

    Electric motors

    The electric motor is far and away the most common chiller compressor drive. Most of these are fixed speed motors (typically 1,800 or 3,600 rpm). Since compressor power requirements are proportional to the difference between evaporator and condenser pressures and refrigerant flow requirements, motor loads vary accordingly. Load variations are handled by cylinder unloading or multiple compressor staging for reciprocating units, slide vane capacity control in screw compressors, and inlet guide vanes (and infrequently hot gas bypass) for centrifugal compressors.

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    In cases where the ability to change compressor speed may offer a better way to modulate compressor capacity and/or performance, a variable speed electric motor should be considered. This approach is seldom utilized in new chiller installations since chiller manufacturers can now build in excellent modulation control. Variable speed motors have been more often used in retrofit applications. One word of caution: always consult the chiller manufacturer for warranty and performance verification before accepting the claims of anyone wishing to modify an existing chiller in this way.

    Steam turbines (back pressure & condensing)

    Steam turbines, reciprocating engines, and sometimes gas turbines are used to drive chiller compressors. The most common applications are very large (over 1500 tons) steam turbine-driven centrifugal chillers used in cogeneration applications for large hospitals or industrial cooling. In situations where electrical demand charges are high (say over $25 per kW per month) or where a demand ratchet could make an electric-driven chiller too expensive to operate for a few months a year, steam turbine-driven chillers are often specified.

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    Why not reciprocating engines or gas turbines? Steam turbines use the existing boiler system so they don't have to worry about fuel supply or air emissions. Since the steam needs of the site are usually dictated by the colder months, the existing steam generating capacity is often more than adequate to support cooling. Plus, the operating and maintenance characteristics of steam turbine-driven chillers are much better than reciprocating engines or gas turbine-driven equipment. Finally, where existing boiler capacity is adequate, steam turbine-driven chillers cost less than reciprocating engines or gas turbines. There are two basic steam turbine designs: back pressure and condensing. These indicate whether steam leaving the turbine goes on into the steam distribution system to satisfy process or heating requirements (this is "back pressure"), or whether the steam leaving the turbine goes straight to a dedicated steam condenser where it is rejected via a cooling tower or river water. Logically, condensing steam turbines are more expensive and less efficient than the back pressure designs.

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    When site steam requirements are reasonably steady and in excess of the steam flows necessary to drive the chiller, the back pressure design makes the most sense. Where this is not true, and power costs would be high for an electric-driven machine, a condensing steam turbine may be the most cost effective alternative. In many cases where steam turbines are considered, rather than apply them to a chiller operating relatively lower hours a year, the turbine is typically used to drive a generator to take maximum advantage of its power generating capabilities.

    Selecting a chiller design like this requires careful consideration of site-specific conditions. Steam turbine driven chillers represent a complex design in any situation. It is wise to consult with qualified design professionals and reputable equipment manufacturers before making a final decision.

    Reciprocating engines

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    Reciprocating engines are usually selected to drive chillers in the smaller range — 100 to 500 tons. The compressor (usually a screw or centrifugal model) is usually directly coupled to the engine drive shaft. Engines are often considered where the site can use the energy in the hot water and/or hot air exhausts produced. Roughly one-third (or less) of the total fuel input is converted to compression power. Therefore, the economics of reciprocating engine drives usually depend on the cost-effectiveness of heat recovery. Engine jacket water (which can reach temperatures as high as 220°F) is easily recovered and also represents about one-third of the fuel input. The heat in the engine exhaust represents the remaining third of fuel input, but this heat is generally not fully recoverable.

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    Engine-driven chiller cost effectiveness can best be determined using a cautious, conservative assessment by a professional that considers these three factors:

    1. Heat recovery that reflects actual site-specific heating efficiencies and needs,
    2. Conservative annual heating requirements, and
    3. Realistic operating and maintenance costs (which are typically higher than any other mechanically driven chiller alternative).
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    Once realistic heat recovery estimates have been factored into the equation, the only other major issue is that of O&M expense. Here, the Gas Research Institute uses $0.01 per ton-hour more than an electric-driven chiller design. While your costs could be different, a figure of $0.01 to 0.12 per ton per operating hour represents a reasonable first cut estimate. Always rely on qualified design professionals and reputable equipment manufacturers for installed cost, operating cost, and performance estimates.

    Gas turbine designs

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    Gas turbines are seldom selected to drive chiller compressors because the efficiency of the cogeneration system using a gas turbine relies heavily on recovering the engine's waste heat. Most sites simply don't have a use for all the waste heat. In cases where the heat can be used, the gas turbine is typically used to drive a generator to take maximum advantage of its power generating capabilities. The main problems associated with using gas turbines as chiller drives include:

    1. Gas turbine power levels (and the resulting chilled water production) are significantly reduced (~ 25-35%) at high ambient temperature levels. This means that at the very time the site needs maximum power to drive a chiller compressor, the gas turbine is least capable of delivering it. One solution might be to use some of the chilled water production to cool gas turbine inlet air, but this also reduces net chilled water production.
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    2. Operating and maintenance procedures are relatively sophisticated. The engines must be protected against inlet dust, contaminants, frosting, or damage from foreign objects. When placed in the hands of qualified, experienced personnel, and run continuously, gas turbines have recorded extremely high annual availability and low maintenance costs. Unfortunately, chillers seldom run continuously.
    3. If the gas turbine is fueled with natural gas, gas pressures have to be higher than with any other mechanical driver — typically 300 - 400 psig for the gas turbine. These pressures aren't always available from suppliers, and therefore require a supplemental gas compressor. Since this gas compressor is relatively unreliable, a "spare" is usually added in the system design, making it an expensive design attribute. Coupled with the power used to compress the natural gas fuel input, this compressor becomes a significant element in the cost-effectiveness equation.
    4. Careful matching of the turbine and compressor, both available in limited size increments is essential. Starting and stopping torques are specially important. These requirements typically increase the chiller cost not economically supportable.

    This doesn't mean that the gas turbine is a necessarily bad choice for a mechanical drive application, it just highlights the primary concerns the designer and owner should consider in evaluating the alternatives. Therefore, it would be prudent to rely on qualified design professionals and reputable equipment manufacturers for gas turbine installed cost, operating characteristics, and site-specific performance estimates.


    Evaporative Cooling

    Reduce the energy consumed by mechanical cooling equipment by using the cooling effects of evaporating water.

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    Evaporative cooling supply air can reduce the energy consumed by mechanical cooling equipment. The two general types of evaporative cooling are direct and indirect systems. The effectiveness of either of these methods is directly dependent on the low wet bulb temperature in the supply air stream. This is why these systems are popular in desert climates. In some applications, the two types are combined as shown here.

    Applications

    The effectiveness of either of these methods is directly dependent on the low wet bulb temperature in the supply air stream. This is why these systems are popular in desert climates.

    Technology types (resource)

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    Evaporative cooling - direct

    Direct evaporative cooling introduces water directly into the supply airstream (usually with a spray or some sort of wetted media). As the water absorbs heat from the air, it evaporates. While this process lowers the dry bulb temperature of the supply airstream, it also increases its wet bulb temperature by raising the air moisture content.

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    While an evaporative cooling system can effectively reduce the required capacity of the mechanical cooling equipment, it usually does not eliminate the need for a conventional cooling coil (except in certain arid regions of the country). Additional static pressure typically around 0.2 to 0.3 inches water column is required by the air handling system whenever evaporative coils are used in conjunction with a conventional cooling coil.

    Evaporative cooling - indirect

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    Indirect evaporative cooling uses an additional waterside coil to lower supply air temperature. The added coil is placed ahead of the conventional cooling coil in the supply airstream, and is piped to a cooling tower where the evaporative process occurs. Because evaporation occurs elsewhere, this method of "precooling" does not add moisture to the supply air, but is less effective than direct evaporative cooling. That is, it will not cool air to as low a temperature at the same outside air wet bulb.

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    Free Cooling Effect

    Produce chilled water without operating the chillers.

    "Free Cooling" is the production of chilled water without operating the chillers. Free cooling is not really free as the chilled and tower water pumps and the tower fan(s) must operate.

    The heat removed from the building by the chilled water coils is rejected by one of these alternatives.

    • Refrigeration Migration
    • Strainer Cycle
    • Plate and Frame Heat Exchanger

    Technology types (resource)

    Refrigeration migration

    One method for reducing the energy consumption of a centrifugal water chiller is to add a refrigerant-migration free cooling cycle. This type of free cooling is based on the principle that refrigerant migrates to the coldest point in a refrigeration circuit.

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    When water returning from the cooling tower is colder than the chilled water, refrigerant pressure within the condenser is lower than that in the evaporator. This pressure differential drives the refrigerant vapor "boiled off" in the evaporator to the condenser, where it liquifies and flows by gravity back to the evaporator. As long as the proper pressure difference exists between the evaporator and condenser, refrigerant flow and the consequent free cooling continues.

    Under favorable conditions, refrigerant-migration free cooling can provide as much as 40 percent of the chiller's design tonnage if the chiller is designed appropriately. Since the chiller and free cooling cycle cannot operate simultaneously, free cooling of this type can only be used when the cooling capacity of the tower water is sufficient to meet the entire building load.

    Little, if any, free cooling capacity is available when the ambient wet bulb temperature is above 50°F. Accessories such as chilled water pumps, condenser water pumps and cooling tower fans continue to operate in the conventional manner while the chiller operates in the free cooling mode. The energy cost savings realized from free cooling operation results from the compressor's inactivity during this cycle. The cooling tower must be designed for winter operation.

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    Strainer cycle

    Like other methods of free cooling, the addition of a strainer-cycle waterside economizer is intended to reduce water chiller energy consumption. This particular method uses cooling tower water to satisfy the building's cooling load. Whenever ambient wet bulb temperature is low enough, cooling tower water is "valved" around the chiller directly into the chilled water loop. The cooling tower water typically passes through a filter (or strainer) before entering the chilled water circuit. This is why it is commonly referred to as "strainer cycle."

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    Pumping cooling tower water throughout the entire chilled water loop increases the risk of pipe corrosion and air handler coil plugging. This risk can be mitigated through more costly water treatment. Strainer cycle economics are limited since free cooling is only available when the cooling load can be satisfied with cooling tower water. The cooling tower must be designed for winter operation.

    Plate and frame heat exchanger

    One method for reducing water chiller energy consumption is to add free cooling. The method shown here uses a plate and-frame waterside economizer that pre-cools the chilled water before it enters the chiller's evaporator. When the ambient wet bulb temperature is low enough, the heat exchanger allows the transfer of heat from the return chilled water to the water returning from the cooling tower. Lowering the temperature of the water entering the evaporator reduces both chiller loading and energy consumption.

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    The plate-and-frame method of free cooling requires an additional heat exchanger. This adds to the initial cost of the system and increases pumping costs due to the added pressure loss. Free cooling is only of significant value when the ambient wet bulb temperature is lower than the design return chilled water by about 10°F. The cooling tower must be designed for winter operation, and the water entering the chiller condenser must be maintained within the manufacturer's specified temperature limits while the chiller is operating.

    Note that plate-and-frame free cooling can be accomplished with a variety of piping arrangements, depending on the operational characteristics desired. The schematic illustrated here shows just one method of piping that can be used to permit simultaneous free cooling and mechanical cooling.

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    Compare technologies for this integral element in building cooling solutions.



    Braising Pans

    Even heating, insulated bottom, cooks in tilted position, better heat transfer, fast recovery.

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    The braising pan is perhaps the most versatile piece of commercial cooking equipment available.

    The braising pan is also known as a tilting skillet, fry pan, and braiser (as well as many other names). It can braise, boil, simmer, griddle cook, fry, steam, thaw, poach, blanch, heat canned foods, act as a proof box or oven, and store hot bakery products. This flexibility is valuable in a commercial kitchen, where labor and floor space are limited and a menu item can be prepared entirely in this single pan. Cooking with a braising pan, a food operation can realize a 50% or greater labor savings over conventional top or stock pot methods (mostly because of reduced cleaning requirements). The value of a braising pan is even higher in new kitchens where it can substitute for numerous other pieces of kitchen cookware.

    The pan can be tilted a few degrees to drain fat away from food as it cooks, such as in griddling or braising meats. Boiling about an inch of water in a covered braising pan can be used to steam food held in special perforated pans or racks. Proofing can be done similarly by using hot instead of boiling water.

    Braising pan types

    There are three types of braising pans: table models, floor models (mounted on a set of open legs or a cabinet base), and wall-mounted units. The cooking capacity of a braising pan is rated by its manufacturer. Table models range from 10 to 15 gallons. Floor models typically range from 19 to 40 gallons.

    Comparing electric vs. gas braising pans

    There are many factors to consider when selecting a braising pan: initial cost, food preparation productivity, ease of operation, heat generation in the kitchen, and whether electricity or gas is used as the energy source. However, consider that energy only accounts for 3 to 5 percent of a typical food service establishment's total costs. Therefore, while one fuel may be less expensive in a BTU to BTU comparison, the best choice in cooking equipment is the one that minimizes total operating costs, not just energy costs. Features that reduce labor costs or result in higher food product yield will nearly always outweigh any energy considerations. Make sure that you include all of these factors in any equipment evaluation.

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    Therefore, when comparing gas an electric models, compare equipment that is similar in all ways except the energy source.

    Advantages of electric braising pans

    Electric and gas braising pans have virtually the same preheating capabilities, with both reaching a cooking temperature of 300°F in about 10 minutes. However, electric braising pans have several advantages over gas models:

    An electric braising pan unit costs an average of 20 to 25% less than similar gas models.

    Electric braising pans use less energy than their gas equivalents. The average efficiency of electric models is about 80%, while gas model efficiency is just over 50%. This higher efficiency translates into less heat into the kitchen, which lowers cooling requirements from the HVAC system.

    Electric braising pans are much easier to clean and maintain than gas models.

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    Braising pan components

    A braising pan looks like a large flat griddle with 7- to 9-inch side walls. It is typically made of stainless steel over aluminum block, or a steel griddle base. On gas heated units, aluminum baffles are added to the bottom to promote even heating.

    All units are equipped with both a hinged lid and a tilting mechanism. The lid or cover holds heat in the pan. Tilting mechanisms for braising pans come in three types: manual, hand crank, and electric. The hand crank with a self-locking worm gear is the most popular. The tilting mechanism tilts past 90 degrees so an operator can pour foods out of the pan and clean the unit easily. The pouring side of the pan usually has a notched spout.

    The cover should fit tightly and be counterbalanced with springs so it doesn't shut on an operator's hand. Lifting handles typically run the length of the pan front (but an operator should also be able to raise the cover from the side to avoid a blast of steam on their hand). Most covers are available with a condensate drip shield and a vent.

    Controls for the braising pan include a power off switch and a 100° to 450°F thermostat. Some units include a 60 minute timer and buzzer.

    With the exception of 15-gallon models, braising pan units are generally rectangular. One manufacturer produces a round, 15-gallon model. Also, some models contain infrared coils in the pan cover to accommodate special tasks such as baking and top browning.

    Accessories

    Braising pans may offer useful accessories that add versatility and labor savings, including:

    • Hot and cold water spray hoses.
    • Food receptor pan supports, hinged to facilitate tilting. Casters for greater mobility.
    • Pan racks that hold 12 by 20 inch steaming pans.
    • An electronic ignition on gas units.
    • Food strainers that slip on and off the pouring spout.
    • Steamer racks, pasta baskets, and poaching pans.
    • A drain valve and hose.

    Skittles (combi-pans)

    A skittle, sometimes called a combi-pan, performs the functions of seven pieces of kitchen equipment. A skittle can serve as a steamer, a skillet, a griddle, a fryer, a kettle, a roaster, and a holding cabinet.

    The value of such a versatile unit is easy to see. Commercial kitchens are growing more and more complex. Kitchen space is expensive, and demands for more flexible menus and quicker preparation strains both staff and equipment. Manufacturers have responded by creating the skittle, which can completely replace serve as a backup for several pieces of cooking equipment. The skittle's flexibility makes it ideal for smaller food service establishments without room for multiple pieces of equipment. Skittles are available in gas, electric, and high performance electric.

    Perhaps the skittle's greatest value is as a steamer. This is because the skittle is the only steamer not requiring a boiler, thus eliminating a major maintenance problem. This means lower maintenance costs and no descaling or deliming.

    As a skillet, a skittle provides even heating, excellent heat retention, and quick recovery. As a griddle, it offers the advantage of tilting, which allows grease to be drained off even while cooking. The skittle is also excellent for shallow or deep-fat frying. Cooking oils can be drained safely off into a container for filtering or storage. As a kettle, the skittle can be used to prepare soups, sauces, rice, and other foods, with capacity ranging from 7 to 40 gallons. As a roaster, the skittle prepares food in dry heat or in combination with steam, making it ideal for roasting meats, baking potatoes, or reheating prepared foods in 14 cubic feet of oven space. Skittles can also be used as holding cabinets because they have capsule lids that preserve the moisture content of food during holding.


    Broilers

    Reduced shrinkage, improved heat transfer, increased production, less spatter, less effluent.

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    Broilers (Overview of All Types)

    Broilers provide an alternative method for cooking flavorful, nourishing, and healthful foods. Broilers are used to cook a wide variety of foods by a process that usually takes 3 to 6 minutes. Products commonly prepared with broilers include steak, poultry, seafood, hamburgers, pizza, and ethnic dishes.

    Some types of broilers are used to "finish off" items like toasted breads, cheese sauces, and hot sandwiches. Depending on the broiler type, these food items may be cooked in metal pans, glass casseroles, or directly on the surface of broiler grates or conveyor belts.

    In the 1950s, only about 10% of the nation's food service establishments featured a broiler. Today, one third are equipped with broilers.

    Broiler Types

    Four major types of broilers are available.

    Click on the desired type below for more information.

    Standard over-fired broilers are heavy-duty units designed to cook large quantities of food by exposing it to radiant energy. This energy is emitted by heating radiants above the grid. Infrared broilers work much like standard broilers, but they operate at higher temperatures (up to 1,600°F) to produce high intensity infrared radiation. Infrared broilers have very fast preheat compared to standard over-fired broilers.

    Temperature and cooking time is controlled by moving the grid up or down through several grid positions. The grid is spring-loaded or counter balanced for convenient up or down adjustment. The grid also rolls in and out for easy loading and is removable for fast clean-up. Each deck of the broiler typically has separate temperature controls, usually with high-low or high-medium-low settings. This varies depending on the manufacturer and the type of fuel powering the broiler.

    Drip shields are located below the grids and move with the grid to collect grease and food particles. V-shaped channels deposit the liquid residue in a drip pan for disposal.

    Over-fired broilers are usually installed on stainless steel counters and are available as single and double-decked modular units. They can also be mounted on a one-pan oven base, convection oven base, or a storage cabinet base. In fact, some combinations of single gas broiler decks have storage cabinets below and a finishing oven above the broiler deck.

    The waste heat generated by gas burners is sometimes used in the finishing oven cavity. This is an effective method of saving energy by recycling heat that would otherwise go unused.

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    Under-fired broilers or charbroilers are typically medium- to heavy-duty units. They have the ability to cook large quantities of food by exposure to radiant energy produced by heating elements located below the grid. Charbroilers are available in countertop, cabinet base, or stainless steel frame models.

    Charbroilers cook food much like an outdoor barbecue grill. Food is placed on a cast iron grate above the heat source, and cooking occurs primarily from radiant heat and conduction by the grate. The energy source may be electricity, gas, wood, or charcoal. As the food cooks, fats or marinades drip onto the coals or ceramics producing smoke. The smoke produces the characteristic charred flavor, while the hot grates create the strip marks that are typical on charbroiled foods.

    There are two types of under-fired charbroilers. One type allows the radiant heat source to heat a radiant to a cherry red color. The radiant, in turn, broils the food product. The other type of charbroiler uses a heating source above or below to heat lava rocks or ceramic briquettes. The rocks or briquettes distribute the heat more evenly than the heat source alone. Some manufacturers use both methods to increase efficiency and reduce preheat times.

    The broiler grate is adjustable to both level and tilted positions. Typically, the charbroiler is designed for the rear two-thirds of the grate to be hotter than the front section. Many models also have grease troughs fastened to each blade in the top grates to channel excess fat runoff and reduce flaming. Excess residual fat drains into a large grease drawer in a cool zone for disposal.

    A charbroiler, like an open range-top burner, consumes energy at a constant rate, which depends on the temperature control setting. Because the charbroiler has a significant thermal mass of heating material that requires preheating and retains heat, the unit cannot be turned "on" and "off" quickly on demand.

    Maintenance costs for a charbroiler are typically higher that any other broiler types. This is partly because the heating radiants below the open cooking grates are exposed to any materials falling through the radiants.

    Back-shelf broilers, salamanders, and cheese-melters are often used to supplement existing broilers. These light-duty units "finish off" partially broiled products and browned foods that are not normally broiled for the complete cooking cycle. These small units are capable of broiling other foods as effectively as larger standard units, but not as quickly.

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    Small amounts of food are "finished off," melted, or broiled by exposing the food to radiant energy from the heating radiants located above the grid or rack. Back-shelf and salamander units are always single-deck broilers. Some salamander/cheese melter units are loaded and unloaded from one side, while others are equipped with pass-through capabilities. The units may be mounted on steel wall back-splashes above the ranges, mounted on 4 to 6 inch legs and placed on counters, or simply wall-mounted above prep stations.

    Infrared models work like standard models, but the infrared radiants operate at considerably higher temperatures, increasing their heating capability and shortening preheat times. Back-shelf radiants are located above the cooking grids or racks. Each radiant has a separate temperature control with high-medium-low settings. In addition, the grid moves up or down through several levels. As with over-fired broilers, the grid of a salamander is spring-loaded or counterbalanced for easy operation. Drip shields are located below the grids or racks to collect grease and food particles. The grease and other liquid residue collects in a drip pan.

    Some units have switches that turn on 100% heat when food is placed on the rack and then automatically lower the heat to a standby temperature in between cooking jobs.

    Conveyor broilers combine the principles of over-fired broilers and under-fired broilers using a stainless steel belt to convey and consistently cook large quantities of food between two sets of heating radiants. One radiant is located above the food and one below . Each conveyor broiler may have one or more broil belts. IN multiple belt units, the speed of each belt is regulated with a separate digital speed control so different foods can be cooked simultaneously.

    Conveyor broilers can bake, broil, heat and melt a variety of food items faster and with less labor than other broiler types. The production capacity of a conveyor broiler depends on operating temperatures and the characteristics of the food being cooked, such as composition, diameter, and thickness of the food product. Fresh or frozen hamburgers, steaks, pork chops, hot dogs, sausage, bacon, chicken, fish, or any product that can fit in single-serving oven-safe cookware can be prepared using conveyor broilers.

    The heating radiants of the conveyor broiler, which operate at temperatures up to 1,600°F, are controlled by on and off switches. The speed of each stainless belt is controlled by a variable speed belt control. Cooking time is a function of the intensity of the heat source and belt speed.

    Conveyor broilers can be free-standing floor models or countertop models and can be flow through or front load-front return operation.


    Fryers

    Improved heat transfer, fast recovery, greater oil life, long service life, improved food quality.

    Fryer types

    Used in about 85% of food service establishments, fryers are an extremely popular commercial cooking appliance. A fryer is designed to cook chicken, fish, breaded vegetables, specialized pastries, French-fried potatoes, and other foods.

    Two major types of fryers are available:

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    Conventional open fryers — The most common fryer type is the open, deep-fat fryer. These come in many sizes ranging from counter top models to large stand-alone units with multiple frypots. The fryers have a variety of optional features such as automatic controls, filtration systems, and accessories for holding cooked food.

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    Pressure fryers — These units have a special lid that keeps vapors inside the fry vessel. The vessel captures steam from the cooking food, increasing pressure inside the unit to prevent additional moisture from being released from the food. This seals in juices, improving food taste and reducing the oil absorbed by the food. The also produces shorter cooking cycles, making pressure fryers more productive than open fryers. Pressure fryers are especially popular for cooking fried chicken.

    Besides these two major fryer types, specialty fryers are also available for special needs. One example is the doughnut fryer, which has a wide, shallow frypot designed for cooking doughnuts and other fried pastries. Another example is the convection fryer, which is an open vessel design that improves cooking by circulating hot oil around food in much the same way as a convection oven circulates hot air.

    Comparing electric vs. gas fryers

    There are many factors to consider when selecting a fryer: initial cost, food preparation productivity, ease of operation, heat generation in the kitchen, and whether electricity or gas is used as the energy source. However, consider that energy only accounts for 3 to 5 percent of a typical food service establishment's total costs. Therefore, while one fuel may be less expensive in a BTU to BTU comparison, the best choice in cooking equipment is the one that minimizes total operating costs, not just energy costs. Features that reduce labor costs or result in higher food product yield will nearly always outweigh any energy considerations. Make sure that you include all of these factors in any equipment evaluation.

    Therefore, when comparing gas an electric models, compare equipment that is similar in all ways except the energy source.

    Advantages of electric fryers

    In general, electric frying equipment offers these advantages:

    • The electric heating elements operate at lower temperatures, which saves energy, reduces fat breakdown, and uses less fat. Gas burners can create hot spots in the fryer, which breaks down the oil prematurely.
    • Electric fryers add less heat to the kitchen because they are more energy efficient.
    • Electric units require less maintenance and require less ventilation.
    • Electric units have faster preheat and recovery times than gas units.
    • Electric induction units are now available that use magnetic induction coils to heat the oil. Some electric fryer manufacturers are also using lower watt-density elements to improve efficiency and achieve longer oil life.

    Energy and money saving tips

    Here are a few common-sense operating tips that save money with a fryer.

    • Turn the fryer off or down to an idling temperature during slack periods when the unit is not in use.
    • Operate the fryer at the proper temperature, 325° to 350°F. Excessive temperatures waste energy and often result in improperly cooked food.
    • Do not load the fryer baskets beyond the manufacturer's recommended capacity. This is usually one-half to two-thirds full. Overloading results in poor food quality.
    • Check fat levels frequently. Low fat levels can cause premature oil breakdown.
    • Drain and strain the oil frequently. This saves oil and preserves food quality.
    • Keep the units clean and properly maintained.
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    Fryer components

    Frypot

    The most common fryer is the open vat fryer. The portion of the fryer that contains the oil is called the frypot (also called the fry kettle, vat or fat container). The frypot is usually rectangular and ranges from 14 to 18 inches long by 18 inches wide and 18 inches deep. Wire baskets containing uncooked food are lowered into the frypot for cooking. Next to the frypot are supports that hold the wire baskets while cooked food drains excess oil back into the frypot. Some units have a removable frypot while others have frypots that are fixed in place.

    Some frypots are split into two sections so the operator can cook two different kinds of foods without transferring taste. In addition, the operator can turn off one side of the unit during slow periods. This saves energy costs and prolongs oil life.

    Most fryers have a 1- to 3-inch separation between the frypot and the outer housing or cabinet. Some units have insulated frypots, while others have an insulated cabinet. The use of insulation reduces energy costs and heating up of the kitchen.

    Heat source

    Electric units have heating elements submerged in the bottom of the frypot. These are either fixed in position or hinged to the main structure of the fryer. Hinged units can be lifted out for easy cleaning.

    Gas units have burners located outside the frypot. Some more advanced units have fire tubes that extend through the frypot in order to transfer more heat to the oil. These fire tubes often contain baffles to improve heat transfer and reduce the amount of heat wasted by escaping up the flue.

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    Cold zone

    Most fryers have a cold zone, which is a small section of the frypot bottom extending below the heat source. The oil in this section is intentionally cooler than the oil in the cooking zone. When particles of food, batter, and breading escape from the basket, they sink to the bottom and collect in the cold zone and stop cooking, which prevents oil breakdown and lengthens cooking oil life. This design also creates a natural convective flow of oil throughout the frypot so cooler oil continuously recirculates with hot oil. Allowing the oil to cool in this way further reduces breakdown.

    Controls

    Nearly all fryers have a thermostat to maintain the temperature of the frypot. This control is either located on the front panel or above and behind the frypot. Some units also have a timer that alerts the operator when the food has cooked for a preset amount of time. More sophisticated models have elaborate automatic controls, such as an automatic basket lift, that reduce labor requirements and more closely monitor the cooking process. Some units can even be programmed so an operator only needs to specify the food type, such as French fries, and the unit automatically controls the cooking time and temperature. This reduces training costs and improves product quality.

    Better fryers include automatic filtration equipment that reduces the labor requirements for daily cleaning.

    Fryer operation tips and issues

    General operation

    Most fryers take between 5 and 15 minutes to reach full operating temperature. Typically, a signal light stays on when the temperature is below the set temperature point. Operators set the thermostat to the desired temperature and wait till this light turns off, indicating the fryer is ready.

    Many fryers have timers as well as thermostat controls. Operators need to know both the proper temperature and cooking time for each food product. For consistency of quality, these settings must be maintained. To address this need, some units have devices that automatically raise and lower baskets into the fryer at specified times, taking responsibility away from the operator. This saves labor costs and ensures more consistent quality.

    Fry baskets should be loaded to at least one-half of their capacity but never more than two-thirds, because food does not cook properly if overloaded. After loading, a basket is lowered into the fat and the timer started. For automatic units, the baskets are attached to the automatic elevator supports and with the press of a button the frying process begins.

    At the end of the recommended cooking time, the baskets are lifted out of the oil bath and hung on basket supports for draining. Automatic units are programmed to do this without operator assistance.

    During slack periods, the fryer should be turned off or its temperature turned to a 200 degree standby setting. This saves energy and increases the life of the fat.

    Finally, all units should have a safety thermostat to warn the operator when the temperature exceeds 400°F. Some models have a warning light that turns on or flashes when the unit overheats. If this occurs, the unit should be turned off and allowed to cool. If the unit overheats again, it should be serviced.

    Fryer preparation

    The cooking medium for all fryers is oil (also called shortening, frying compound, or fat), which is heated to about 350°F. The oil is typically vegetable or animal fat purchased in solid or liquid form. Top grade commercial shortening with a high smoke point and resistance to breakdown results in better tasting food and longer fat life.

    Most fryers have a marker in the fry vessel that shows the proper shortening level. In units without a marker, shortening should cover the heating elements by at least one inch .

    If you use liquid shortening, fill the kettle to the proper level and set the thermostat to the desired temperature.

    For solid shortening, first pack the shortening solidly around the cooled heating elements. Next, set the thermostat to 250°F to let the solid fat melt slowly. Continue to add fat and wait for it to melt until it reaches the proper level before turning the thermostat up to the desired cooking temperature.

    Performance

    The quality of the final food product largely depends on the quality of the oil that is used. Flavors develop in the oil transferred to the foods being cooked. Also, oil is expensive, ranging from 30 to 75 cents per pound. Since a single fryer's oil capacity can range from 28 to 110 pounds, the cost for replacing used oil can be significant.

    Food particles eventually degrade oil. Particles continue to cook long after the food is removed from the fryer, and can eventually burn, leaving a bitter taste in the oil. To minimize this problem, most fryers have a cold zone at the bottom of the fryer where food particles collect. The temperature in this zone is lower than the cooking zone, so food particles stop cooking. However, the fryer operator should still frequently filter the oil to remove excess food particles and prolong the life of the oil.

    Excess temperature can also destroy cooking oil. If the fryer's temperature exceeds 400°F, the oil will begin to break down and develop a bad taste. Thermostat overrides and hot spots along burner tubes in gas fryers are frequent culprits.

    Cooking temperature also greatly affects the quality of the final food product. Cooking at too high a temperature may overcook the outside of food while leaving the interior portion partially uncooked. However, cooking at too low a temperature causes food to absorb more oil, which makes it soggy and adds to food preparation costs.

    For more information about the benefits of electric fryers vs. gas, please contact us for a copy of an EPRI performance or ventilation report.


    Griddles

    Uniform heating, no hot or cold spots, high production capacity, fast recovery, faster cleaning.

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    The griddle is the workhorse of the fast food industry. Nearly every commercial cooking operation uses some type of griddle.

    A griddle is simply a flat metal plate that cooks food by conducting heat directly from the griddle surface to the food product. A thin layer of cooking oil or grease from the cooked item usually separates the food from the griddle surface to keep the food from sticking. Griddles are used to cook a variety of foods including: bacon, eggs, chicken, hamburgers and steak. Some also like to use the hot griddle surface to heat food in a small pan, like melting butter.

    Some griddles are equipped with a platen placed a few inches above the griddle surface to provide additional cooking from above. This add-on cooks the top surface of the food by exposing it to radiant heat energy, cooking the food faster and sealing in the juices for improved taste and reduced shrinkage.

    Griddle types

    Two major types of griddles are available: single-sidedand double-sided. Single-sided griddles cook food on the bottom only. Double-sided griddles cook food on both sides simultaneously.

    Single-sided griddles

    A single-sided griddle can be installed as:

    • a built-in unit
    • part of a range or cooking center
    • a free-standing unit that sits on tubular steel legs
    • a portable unit mounted on a stainless steel mobile stand.
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    Heavy duty griddles are usually free-standing. The cooking surface typically range from 30 to 36 inches deep and up to 72 inches wide. Often, two or more free-standing units are installed side-by-side, or back-to-back.

    Counter-top griddles are small, free-standing units, normally located on a countertop or in a counter base. They range from 15 to 24 inches deep and from 15 to 72 inches wide.

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    Double-sided griddles

    Double-sided griddles heat food from both the top and bottom. They have a large bottom griddle plate and at least one platen on top. Platens press on the food, "sandwiching" it between two hot pieces of metal. This allows food to be cooked on both sides simultaneously. Stop devices on the platen keep the food from being crushed. A counter-balanced lift holds each platen in place when raised.

    A double-sided, non-contact griddle has a plate on the bottom and at least one platen on top. However, a non-contact griddle's top platens do not actually contact the food. The "hood" stays about one inch above the food, heating like a broiler. The heat source may be a gas burner, conventional electric elements, quartz lights, or a ceramic infrared burner.

    A double-sided griddle cooks food very quickly. For example, 8 to 12 hamburgers cook in roughly 3 minutes. The double-sided, non-contact design eliminates the need to turn food for uniform cooking, which can reduce labor costs.

    Comparing electric vs. gas griddles

    There are many factors to consider when selecting a griddle: initial cost, food preparation productivity, ease of operation, heat generation in the kitchen, and whether electricity or gas is used as the energy source. However, consider that energy only accounts for 3 to 5 percent of a typical food service establishment's total costs. Therefore, while one fuel may be less expensive in a BTU to BTU comparison, the best choice in cooking equipment is the one that minimizes total operating costs, not just energy costs. Features that reduce labor costs or result in higher food product yield will nearly always outweigh any energy considerations. Make sure that you include all of these factors in any equipment evaluation.

    Therefore, when comparing gas an electric models, compare equipment that is similar in all ways except the energy source.

    Advantages of electric griddles

    In general, electric griddles offer these advantages :

    • More uniform temperature across the surface of the griddle, which makes electric griddles easier to operate and produces consistent food quality.
    • Thinner griddle plates that use less energy and about half the time to preheat.
    • More efficient operation with less heat loss into the kitchen, lowering kitchen cooling costs and reducing maintenance.

    A recent new electric technology is the induction griddle on which the griddle surface is heated by a magnetic field inducing electric currents across the griddle plate. This produces a more uniform surface temperature and brings the griddle surface up to cooking temperature very quickly, saving money, rejecting less heat to the kitchen, and producing a more consistent food product.

    Energy usage

    Single-sided electric griddles normally consume 3 to 25 kW of power. The average preheat time can range from 7 to 20 minutes depending on the plate configuration and BTU input. Energy consumption for gas single-sided griddles normally approaches 20,000 to 30,000 BTUs per 12-inch section, with preheat times of 15 to 23 minutes. Again, these figures depend on plate configuration and BTU input.

    A low energy input figure generally implies slow pre-heat and recovery time. Typical kW consumption for the electric double-sided griddle ranges from 21 to 35 kW, with a preheat interval of about 18 minutes. Typical ratings for gas powered double-sided griddles range from 90,000 to 140,000 BTUs, with preheat times of 18 to 23 minutes.

    Energy and money saving tips

    Here are a few common-sense operating tips that save money:

    • Heat only the griddle sections necessary for a task.
    • Pre-heat only until the griddle surface has achieved the correct cooking temperature.
    • Set the temperature for each section no higher than that required to cook the food.
    • Turn the griddle down or off during slow production times.
    • Use pre-cooked foods and avoid frozen products where possible.
    • Use a cover while cooking where it will not adversely affect the cooking process.
    • Scrape the cooking surface between production intervals. Cleaning some types of griddle surfaces requires special tools. Consult the manufacturer or owner's manual for details.
    • Clean the griddle frequently, and always re-season the griddle afterwards.
    • Inspect each section of the griddle periodically, searching for hot or cold spots.
    • On gas units, make sure each gas flame burns blue and adjust the gas-to-air ratio when necessary.
    • It takes 77 BTUs to heat a pound of ground beef from 40°F Fahrenheit to 140°F, but 196 BTUs are used to heat the same pound of beef from 0°F to 140°F. Therefore, simply thawing food before cooking can increase energy savings.

    Heat loss issues

    Griddles are among the largest energy users in food service, so energy efficient operation is an important way of reducing operating costs. Most of a griddle's operating costs arise from heat loss from the bottom, the top, and the four edges of the cooking surface. In addition, cooking surface losses are increased due to the relatively small quantities of food typically cooked on the large surface during most of the day.

    Heat lost from a griddle warms the kitchen, which makes workers uncomfortable unless the cooling system removes the excess heat. These losses can therefore add greatly to overall cooling costs, which is an important factor favoring electric griddles over gas units. Even if a kitchens is not air-conditioned, so cooling costs are not an issue, worker productivity and morale suffer as room temperatures rises, increasing costs through lower worker performance and increased turnover.

    Many higher quality griddles are designed for improved energy efficiency, partly through the use of newly developed griddle plate surfacing. These improved surfaces restrict the griddle's normally excessive radiation of energy. In full-load cooking tests, griddle efficiency ranges all the way from 31% to 71% depending on model. Griddle inefficiency is most evident in light-load cooking operations, where efficiency ranges from 13% to 50%.

    Griddle components

    Components

    Griddles come in many sizes and may be freestanding or built into a range body with ovens below. Generally, the griddle surface is divided into 12-inch sections, each with its own heating unit and control mechanism. This design lets different sections operate at different temperatures, so the chef can cook different kinds of food at the same time.

    All griddles have at least one thermostat dial that controls the cooking temperature. Some griddles also have surface temperature indicator lights that are typically located on the control panel. Gas griddles have slotted vents for each burner for the intake of combustion air.

    Griddles normally have a metal splash guard surrounding all but the front of the cooking surface. The splash guard keeps food from sliding off and minimizes grease splatter. A grease trough, usually running along each side of the griddle plate, drains grease and residual food particles, depositing these wastes into a collecting pan. Grease troughs may also be located on the front or back of the griddle. Some griddles have a slightly tilted griddle plate that causes grease to run off. These units also usually produce less smoke while cooking.

    The cooking surface of a single-sided griddle is called a plate and its design dictates the performance of the griddle. High quality plates distribute heat uniformly across the griddle. The most common griddle plate is made of flat steel or cast iron and ranges in thickness from one-half to one inch.

    Griddle surfaces are usually smooth and flat, but some types of griddles have ribbed or grooved surfaces. Grooved surfaces are designed to emboss food with charred grid marks, similar to broiled and grilled foods.

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    Ribbed surfaces cook somewhat slower than flat surfaces because only the parts of the food that touch the raised edges of the grooves are exposed to full heat. For this reason, manufacturers usually install a grooved surface on only a single section of the griddle, with remaining sections equipped with a flat plate for total direct-contact cooking.

    Griddle operation tips and issues

    General operation

    Griddles can operate between 200° and 550°F, but cooking temperatures normally fall between 225° and 375°F. Most units preheat to their thermostatically controlled cooking temperature in 15 to 30 minutes.

    Griddles are usually turned on at the beginning of the cooking day and left on all day. This arrangement wastes significant energy if the unit is only used occasionally. This practice is common because griddles take a relatively long time to preheat; it can be impractical to turn off the unit when its not being used. In addition, food service operators like to have the griddle cooking capacity in reserve and so they will rarely turn it off until the end of the cooking period.

    Performance

    Griddle surfaces often develop hot spots and cold spots. Hot spots usually occur near the heat source while cold zones occur in areas farthest from the heat source. Food cooks faster in hot zones and may be difficult to control because of the higher heat. Some griddles develop a cold zone around the perimeter, about two inches wide, which is not useful for cooking but can be used to keep cooked food warm.

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    An experienced chef knows where hot and cold zones are and can adjust the cooking approach accordingly. However, most griddle operators, especially in fast food restaurants, are not this experienced. They fail to adjust cooking times to account for hot zones and cold zones, cooking everything for the same amount of time. This results in inconsistent quality, with some food under-cooked and some over-cooked.

    Good griddle design can minimize changes in surface temperature across the griddle and help maintain consistent food quality. These units also reduce the amount of training needed for new griddle operators.

    Maintenance

    Griddle surfaces should be cleaned regularly. A clean griddle surface offers more uniform heat distribution and operates more efficiently. A clean griddle also prevents the bitter taste of charred food in the final food product.

    Griddle operators should:

    Scrape excess food and fat particles from the surface with a flexible spatula, grill brick, or other device after each cooking load.

    Clean and wipe out grease troughs, remove any stuck-on food, and clean the surface with a soft cloth, rubbing with the grain of the metal while the surface is still warm. This should be done at least once a day and more frequently during heavy cooking loads.

    The platen on a two-sided griddle can often be much harder to clean. Some models have stainless steel platens that make cleaning easy. Others have a special coating like Teflon to prevent food from sticking. A few models use disposable non-stick paper to prevent sticking.

    For more information about the benefits of electric griddles vs. gas, please contact us for a copy of an EPRI performance or ventilation report.

    Ventilation study

    As part of a larger study to identify optimal designs for commercial kitchen appliances, researchers tested one electric griddle and one gas griddle in operation with two hood types: an exhaust-only, wall-mounted canopy hood and a custom-engineered backshelf hood.

    These tests revealed the following:

    • The cooking capture and containment (C&C) flow rate under a canopy hood for the electric griddle is 241 scfm/lf, 13% lower than for the gas griddle, 40% lower than the 400 scfm/lf building code value, and 7% lower than the 260 scfm/lf Underwriters Laboratories (UL) listing.
    • The cooking C&C flow rate under a custom-engineered backshelf hood for the electric griddle is 100 scfm/lf, 9% lower than for the gas griddle, 67% lower than the 304 scfm/lf building code value, and 26% lower than the 136 scfm/lf UL listing.
    • The idle C&C flow rate under a canopy hood was 26% and 32% less, respectively, than the cooking C&C flow rate for gas and electric griddles, and was 0.5% and 22% less, respectively, under the backshelf hood.
    • At the cooking C&C flow rate, the electric and gas griddles required about 60% lower flow under the backshelf hood than under the canopy hood. These results indicate that custom-engineered backshelf hoods can operate with exhaust flows about 65% below code values, and that electric griddles with both hood types require about 10% less exhaust than gas units. Designers should apply site-specific data when evaluating equipment options.

    Background

    To help electric utilities and the food service industry minimize commercial kitchen exhaust hood operating costs, EPRI is undertaking a series of tests to determine the exhaust requirement for a wide range of food service equipment and ventilation hoods. The exhaust requirement is the air flow needed to capture and contain cooking products and heat. Findings compare actual exhaust requirements with building code and UL levels. The ventilation tests described here examined electric and gas griddles operating under a wall-mounted canopy hood and under a custom-engineered backshelf hood using American Society for Testing of Materials (ASTM) standard method production conditions.

    Test Equipment and Conditions

    Both griddles measured 28 in by 3 ft. The electric griddle was rated at 17.1 kW and the gas griddle at 90,000 Btu/h.

    The canopy hood, an exhaust-only, wall-mounted type, was 5-ft wide by 4-ft deep and UL listed at 260 scfm/lf for cooking operation. The backshelf hood, a custom-engineered, exhaust-only type, was 3.4- ft wide by 3.5-ft deep by 5-ft high and was UL listed at 136 scfm/lf for cooking operation. Both hoods had three nominal 20-in by 20-in standard baffle filters.

    For each test, researchers positioned the griddle under the hood in accordance with ASTM F1275-95 and performed the tests using ASTM F1704-96. The temperature of the griddle was set to a calibrated 375°F.

    The project team evaluated C&C with visualization techniques aided by a smoke generator. They ran each test a minimum of three times in a consecutive series to attain statistical certainty as prescribed in ASTM F1704-96.

    Results

    Figure 1 shows C&C flow rates for electric and gas griddles operating under both canopy and custom backshelf hoods, as well as flow requirements under two specification options. Operating under a canopy hood, the electric griddle's measured cooking C&C flow rate is 241 scfm/lf, 40% lower than the rate required by building codes and 7% lower than that listed by UL. The idle C&C flow rate is 165 scfm/lf, 32% lower than the cooking rate. The gas griddle's measured cooking C&C flow rate is 276 scfm/lf, 31% lower than the rate required by building codes and 6% higher than that listed by UL. The idle C&C flow rate is 203 scfm/lf, 27% lower than the cooking rate.

    Operating under a custom-engineered backshelf hood, the electric griddle's measured cooking C&C flow rate is 100 scfm/lf, 67% lower than the rate required by building codes and 26% lower than that listed by UL. The idle C&C flow rate is 78 scfm/lf, 22% lower than the cooking rate.

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    The gas griddle's measured cooking C&C flow rate is 110 scfm/lf, 64% lower than the rate required by building codes and 19% lower than that listed by UL. The idle C&C flow rate is 109 scfm/lf, 0.5% lower than the cooking rate.

    References

    • Commercial Kitchen Ventilation Performance Report, Electric Griddle Under Canopy Hood, EPRI TR-106493-V4, July 1996.
    • Commercial Kitchen Ventilation Performance Report, Gas Griddle Under Canopy Hood, EPRI TR-106493- V3, July 1996.
    • Commercial Kitchen Ventilation Performance Report, Electric Griddle Under Custom Engineered Backshelf Hood, EPRI TR-106493-V6, July 1996.
    • Commercial Kitchen Ventilation Performance Report, Gas Griddle Under Custom Engineered Backshelf Hood, EPRI TR-106493- V5, July 1996.
    • Too Much Hot Air: Reexamining Commercial Kitchen Ventilation Systems, EPRI TB-105709, October 1995.
    • Minimum Energy Ventilation for Fast Food Restaurant Kitchens, EPRI TR-106671, July 1996.
    • Standard Test Method for Performance of Commercial Kitchen Ventilation Systems, ASTM F1704-96.
    • Standard Test Method for the Performance of Griddles, ASTM F1275-95.

    Ovens

    Even heating, uniformity in baking & roasting, Fast recovery, Calibration consistency, Better heat retention.

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    Oven cooking is as ancient as civilization, as old as the baking of bread. Today, oven cooking is the most common food preparation method, and ovens are one of the most widely used kitchen appliances. Even the smallest establishment usually has a microwave to heat appetizers or sandwiches, and large facilities may have a conveyorized bake oven for high volume production.

    Ovens are available in numerous sizes and designs. Some are designed for specialized food preparation tasks, while others are meant for a range of cooking applications. One recent design, called a Flash Bake oven, uses a combination of high intensity visible light and radiant heat to increase production speed and improve food preparation quality. There are also many "cook and hold" ovens that improve preparation consistency and product quality and cook foods at lower temperatures to increase nutritional value and reduce energy consumption.

    Ovens are often the largest consumers of energy in a food service kitchen. Oven design and construction quality, as well as fuel type, affect the amount of energy lost to the kitchen as heat. In typical electric ovens, only 40 to 60% of the source energy is used to cook; in gas ovens, this is only 10 to 30%. The remaining source energy escapes into the kitchen, making staff uncomfortable and adding to cooling costs.

    Some newer oven technologies increase speed and energy efficiency and reduce food-portion weight loss, making oven operation more economical. These improvements usually involve greater initial cost, but may actually reduce overall costs over time.

    Oven types

    There are a wide range of oven types. The most common types are described below.

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    All-purpose ovens

    All purpose ovens are used for baking, roasting, cooking pizza, and many other combined cooking tasks. Each section of an all-purpose oven adapts easily to a modular lineup.

    All-purpose oven production capacity varies by model. Independent controls and heating element banks are usually located at either the top or bottom of the oven unit. These let operators perform special tasks, such as custom browning, with balanced or unbalanced heat.

    Some standard oven decks are air cushioned to improve heat diffusion. Others have a removable core-plate that optimizes heat diffusion and holding.

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    Convection ovens

    Convection ovens circulate air in the oven cavity using a fan. This air movement speeds cooking by increasing heat transfer to the food. Convection ovens are ideal for low-temperature slow roasting, and many feature a slow "cook and hold" setting. Slow roasting meats at low temperature reduces shrinkage (and thus food costs) and tends to produce food of higher quality. Electric convection ovens are often preferred because they have smaller losses in oven humidity during cooking.

    The air flow through the oven chamber allows convection ovens to cook large loads and multiple racks effectively. Modern units have oven chambers insulated on all six-sides, providing peak energy efficiency. Solid state thermostats precisely control temperature, with cooking times digitally displayed for easy monitoring.

    Most electric convection ovens preheat to a typical operating temperature of 350°F within six to ten minutes. Comparable gas ovens are generally slightly slower coming to temperature. Both types offer optional non-stick or stainless steel liner panels that are removable for speedy cleanup.

    An optional heat-keeper recirculation system can save energy costs with gas convection ovens by re-using heated air that would normally be wasted. In these gas models, a power burner is provided for maximum energy efficiency.

    Convection ovens are not ideal for every oven application. They tend to dry products out during cooking, which may deteriorate food quality, especially with pastries. In these cases, a traditional oven is better.

    Half-size convection ovens

    Half-size convection ovens are a good choice when a full size oven for a given commercial cooking application would result in significant energy losses. In these cases, the smaller size of the half-size oven reduces losses while still meeting food production requirements.

    Combination ovens

    A combination oven combines the features of a convection oven and an atmospheric steamer. These ovens use the combination of oven and steamer cooking methods to maximize quality and speed. Steam injection is especially desirable in producing high-quality, golden-brown, crusty breads. Quality is further enhanced by the forced air distribution.

    This multipurpose oven offers a variety of cooking methods:

    • Hot air convection (some with water injection for high moisture)
    • Convection steam
    • A combination of convection, steam, and hot air circulation, and a cook-and-hold feature

    Enclosed tubular convection heating elements produce heat that circulates by a small blower motor. Most units have an extra large observation window to monitor cooking and a timer to track cooking time. Time and temperature controls with digital displays help operators track the cooking process. Some units also offer memory programming for multiple recipes with cooking cycles. The steam boiler can be heated electrically or by gas.

    A roll-in floor model combination oven and steamer has a cooking capacity of dozens of cafeteria pans and bun pans.

    Proofing ovens

    Many breads and pastries require a high humidity environment for optimal yeast action and product baking. To meet this need, special ovens exist with enhanced humidity control for the "proofing" stage in baking. These ovens can also be used to hold cooked food for extended periods of time.

    Most holding ovens surround food with hot air to keep it warm. This causes moisture to evaporate, which shrinks food, reduces visual appeal, and deteriorates flavors, texture, and consistency. However, food will not release moisture and dry out if the air around it is kept saturated. Most proofing ovens have been perfected to the point that they can keep some foods moist and others crisp in the same oven enclosure.

    Steam injection ovens

    Steam injection ovens are essentially standard convection ovens that can produce and inject steam. This steam injection desirable in producing high-quality, golden-brown, crusty breads. Quality is further enhanced by the forced air distribution.

    Electric rotary ovens

    Electric rotary ovens are ideal for supermarkets, delis, and convenience stores. Large glass doors help build purchase-point interest by allowing the product to be viewed during cooking.

    These ovens cook with a combination of convection and radiant heat and often incorporate an air circulation system that allows the unit to act as a warmer. This system maintains high humidity to keep the food contents juicy. In addition, the self-basting cooking action of these units enhances browning .

    Electric rotary ovens are equipped with digital timers and controls simplifying operation. They also usually come with multiple racks. The large removable trays and racks are easy to clean, which reduces labor costs.

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    Microwave ovens

    Microwave ovens cook by heating water and chemical molecules in food with short-wave radio energy like that used in radar and television. The frequency most commonly used in the microwave oven is 2,450 megahertz. Microwave ovens consume the least amount of energy and are highly space efficient.

    One microwave oven advantage is quick de-frosting, heating, and cooking of foods. The ability to defrost and warm foods in a matter of seconds makes these units popular with food service facilities wanting high menu variety for a large volume of customers. These establishments often pre-cook foods and refrigerate them until peak serving periods and then quickly heat portions during peak time periods.

    A disadvantage of the microwave, however, is it cooks foods from the inside out, as opposed to outside in as with most cooking systems. This typically does not provide the surface browning desired in many cooking applications. This can be solved by transferring the food to another type of oven for final browning.

    Cooking capabilities differ only minimally among different microwave oven models. Microwave ovens are available in an array of sizes and with a number of features. Top and bottom, or bottom-only energy feeding systems are available. Each type has rotating wave guides to minimize "hot spots" common to residential style units.

    Flash bake ovens

    A Flash Bake oven uses a combination of intense visible light and infrared energy to cook food rapidly. The visible light penetrates the food to provide heating while the infrared energy cooks the food surface to achieve the desired browning. Microprocessor control makes these units flexible and intelligent in their operation, and can produce superior quality for fish, meat, vegetables, breads, and many other types of foods.

    The primary benefits of Flash Bake technology are its speed and energy efficiency. The shortened cooking time also has the advantage of producing more nutritious and better tasting food. The Flash Bake oven was designed to cook relatively flat, thin foods. Pizza, nachos, quesadillas, and other foods with similar geometry are ideal for this technology.

    The primary disadvantage is one of perception: the oven simply appears to be too small to be a serious food preparation device. However, the unit's high speed and excellent performance have been proven in many establishments. These establishments have found the unit highly cost effective. Perceptions should change as the benefits of this oven are demonstrated to commercial food service professionals.

    Another disadvantage of the Flash Bake is that the increased heat transfer rate must be balanced against possible surface overheating. This can be minimized by operator training and advanced computer controls.

    New oven technologies

    Gas and electric oven manufacturers continually improve oven insulation and controls, heat transfer effectiveness, and heat recovery. These improvements yield higher efficiency and shorter preheat times. Many newer designs also maintain a more uniform temperature in the oven zones.

    For example, conduction ovens circulate a heat transfer fluid through plates to provide more accurate and uniform heating. Also, Flash Bake technology is especially effective in the preparing trendy foods, such as quesadillas and pizzas.

    Comparing electric vs. gas ovens

    There are many factors to consider when selecting an oven: initial cost, food preparation productivity, ease of operation, heat generation in the kitchen, and whether electricity or gas is used as the energy source. However, consider that energy only accounts for 3 to 5 percent of a typical food service establishment's total costs. Therefore, while one fuel may be less expensive in a BTU to BTU comparison, the best choice in cooking equipment is the one that minimizes total operating costs, not just energy costs. Features that reduce labor costs or result in higher food product yield will nearly always outweigh any energy considerations. Make sure that you include all of these factors in any equipment evaluation.

    Therefore, when comparing gas an electric models, compare equipment that is similar in all ways except the energy source.

    Advantages of electric ovens

    In general, electric ovens offers these advantages:

    • Electric units are more efficient, adding less heat to the kitchen that must be removed by the kitchen cooling system.
    • Electric units require less maintenance, require less ventilation, and are more portable.
    • Electric ovens, especially those with electronic controls, deliver more consistent run quality and require less operator supervision. They are also considered to be cleaner and more flexible (especially where maintaining oven humidity levels is important). Kitchen design and modification may also be simplified because venting may be unnecessary.

    Energy and money saving tips

    • Here are a few common-sense operating tips that save money with a oven.
    • The efficiency of ovens depends upon how well they are constructed, and insulation levels and quality are significant factors. Consider this in purchasing decisions, since some inexpensive ovens have little-to-no insulation in the oven door and will cost more to operate.
    • Ovens consume considerable energy when left on, even if no food is being cooked. Energy is lost through the oven walls and leakage around the door opening. These losses can be a significant operating expense, so turn all oven equipment off or lower temperatures during non-operating intervals. This saves energy, reduces cost, and increases oven life.
    • When a food service production does not call for a full sized oven, consider a half-size oven that may operate at much lower cost.

    Oven components

    An oven is composed of a box-like enclosure, heating elements, and controls. The enclosure ranges from a counter-top size to larger free-standing and floor model units. Ovens usually have a hinged door at the front or side (conveyer ovens have openings on two sides), and include adjustable racks or trays to hold food . The quality and amount of insulation and presence of an air curtain (to retain oven heat when the door is opened) all affect energy efficiency and uniformity of heating.

    In standard electric ovens, electric heating elements may be at the top, bottom, or sides of the oven. Gas units use gas combustion chambers. Microwave designs provide heating energy by channeling electromagnetic waves into the oven and rotating the food items to assure uniform heating. Flash Bake ovens use a combination of high intensity light plus infrared radiant energy for extremely rapid heating. In some special oven designs, steam is used to shorten cooking times and improve certain food preparation. Yeast-raised breads and pastries are often baked in humidity-controlled proofing ovens.

    Deck ovens and conveyer ovens use convection as a heat transfer medium, but are named for the special large heated deck on which food is placed during cooking. These are commonly used for roasting, baking, and cooking pizza.

    Oven controls indicate desired oven temperature. Certain designs also provide "cook and hold" cycles that extend holding time and improve the quality of food.

    Oven operation tips and issues

    Since ovens are so common, most people are familiar with their operation. The oven is first preheated to the desired cooking temperature. Next, food to be cooked in the oven is usually placed in containers of metal or glass or on metal pans. The food is then heated at a specified temperature for a certain period of time. The time required depends on the size and shape of the food items heated and the rate of acceptable heat transfer to those items. For example, thin items like pizza heat much rapidly than large items like whole turkeys, and a stuffed turkey takes significantly longer to cook than an unstuffed turkey.

    Some foods require changes in oven temperature during cooking, especially where surface browning is desired. For example, a recipe may require extended initial baking at 325°F, and the last few minutes at 425°F.

    The most common oven-cooking process surrounds the item being cooked in hot air. However, air is a relatively poor heat transfer agent, especially compared to the heat transferred by a griddle or immersion in hot oil. The air heat-transfer can be accelerated by circulating or blowing the hot air around the food being cooked.

    Apart from air, some oven designs use high intensity and infrared light, microwave energy, or steam. Each design has a special niche in the preparation of foods. No one oven design is ideal for all food preparation, so many modern ovens incorporate a combination of these technologies.

    For more information about the benefits of electric convection ovens vs. gas, please contact us for a copy of an EPRI performance report.


    Ranges

    Easy cleaning, incredible speed, improved heat transfer, precise heat control.

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    The range is perhaps the most versatile piece of cooking equipment in a commercial kitchen. It can be used to cook a wide variety of foods, primarily those requiring the use of cookware such as pans, stockpots and skillets. Many range units are also equipped with a conventional or convection oven located below the cooktops, which makes the unit even more versatile.

    The initial cost of a range is usually not the most important factor in making a buying decision. Many choose light equipment because of its initial lower cost, but later discover that the units are inadequate for their production needs. A range should be chosen on the basis of six characteristics: capacity, versatility, temperature consistency, serviceability, ease and economy cleaning, and over-all dependability.

    Range types

    Three major types of ranges are available:

    Heavy duty ranges

    Heavy duty ranges are designed for large heavy stockpots and other cookery. They are ideal for high-volume production in large restaurants, institutional kitchens, and industrial kitchens. These ranges are typically narrower than conventional units, measuring 36 inches wide, and are available in modular units with oven bases or open cabinet bases, or as table top models. Some models include other features, such as fryer sections, salamander broilers, ovens, and griddles.

    Restaurant ranges

    Restaurant ranges are designed for lighter duty cooking than heavy-duty ranges. Even though the overall size of a restaurant range is generally larger than a heavy duty range, they best suited for smaller operations and short order cooking. The larger size accommodates more cooking elements, with each element capable of supporting lighter cookware. These units are available in lengths up to 72 inches and are often combined with a cabinet base or oven unit, salamander broilers, or griddles.

    Specialty ranges

    A variety of specialty ranges are available to suit specific food preparation needs. Some examples are:

    • Chinese ranges, which are built for wok cooking. Some have water spigots and drain troughs to simplify cleaning.
    • Stockpot ranges, which are designed to handle very large stockpots. These are typically only 24 inches tall to let a chef more easily access large pots.
    • Taco ranges, which are made just for the unique task of preparing the contents of a taco.

    New range technologies

    Electric induction ranges represent the latest range technology. These units heat quickly, offer very precise temperature control, and are considered safer since cooking elements don't get hot. induction ranges are also the most efficient type, transferring up to 90% of their energy to the cookware.

    Comparing electric vs. gas ranges

    There are many factors to consider when selecting a range: initial cost, food preparation productivity, ease of operation, heat generation in the kitchen, and whether electricity or gas is used as the energy source. However, consider that energy only accounts for 3 to 5 percent of a typical food service establishment's total costs. Therefore, while one fuel may be less expensive in a BTU to BTU comparison, the best choice in cooking equipment is the one that minimizes total operating costs, not just energy costs. Features that reduce labor costs or result in higher food product yield will nearly always outweigh any energy considerations. Make sure that you include all of these factors in any equipment evaluation.

    Therefore, when comparing gas and electric models, compare equipment that is similar in all ways except the energy source.

    In addition, consider that cooking technique on a range is critical and is learned largely by trial and error. Therefore, chefs are resistant to change after perfecting their craft, and most prefer to use the same type of ranges they were trained on. Chefs trained on gas equipment are likely to prefer gas, and may reject electric ranges or even electric induction ranges. Likewise, experienced electric range users may resist switching to gas.

    Advantages of electric ranges

    In general, electric ranges offer these advantages:

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    • Electric units are generally more efficient, adding less heat to the kitchen which ultimately must be removed by the cooling system.
    • Electric units are less prone to cause fires when grease spills over onto the range.
    • Electric units require less maintenance and less ventilation.
    • Electric induction units offer the highest energy efficiency, come up to temperature very quickly, and offer precise temperature control. These are also safer because the surface never gets hot.

    Energy and money saving tips

    Here are a few common-sense operating tips that save money with any range.

    • Make sure the bottom of the pot rests flush on the heating surface.
    • After a pot comes to a boil, reduce the heat to a level that maintains a simmer. Adding more heat to boiling food does not cook it any faster, but just wastes energy.
    • Cover pots with a lid to retain heat.
    • Cook at the lowest possible heat level that yields satisfactory results.
    • Turn the unit off or at least reduce its temperature when not in use. For closed-top units, preheat only as needed, and heat only the section of the closed-top unit being used.
    • Group pots on closed top ranges to use as little surface area as possible.
    • Here are a few common-sense operating tips that save money with a gas range.
    • Adjust the flame until it is entirely blue. A yellow-orange tip means you are using too much gas and it is not burning completely.
    • Gas flames should just cover the bottom of the pot. Flames extending beyond the pot bottom are dangerous and waste money.

    Range components

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    Range equipment is available in many different sizes and configurations. Most units are 36 inches high and 30 to 32 inches deep and vary from 18 to 60 inches wide. Smaller units contain only two cooking elements, while larger units can contain more than a dozen. Ranges can be free-standing or mounted over an oven or cabinet base. Some free-standing units on a counter-top and are sometimes called cooktops.

    Cooking elements

    All ranges have some type of cooking element. The various element types are described below:

    • Open top element The most common type of cooking element is the open-top element. Open top gas burners have a steel or cast iron grate that holds cookware in place. Gas burners below the grate produce a flame that directly contacts the cookware bottom. Open burners provide precise temperature control by adjusting the height of the gas flame and require no preheat time. Each burner is individually controlled by a gas valve on the front of the unit. Comparable electric units are commonly known as open coil hot plates. Cookware rests on an electric resistance coil which, when heated, transfers heat directly to the cookware bottom. These units usually take a few minutes to preheat when turned on and a few minutes to cool down when turned off. Each cooking element has a separate thermostat to control temperature.
    • Hot top element Hot-top elements use the energy source to heat a thick metal plate rather than heating the cookware directly. These units have a 12 to 18 inch square plate about one-half to one inch thick. The heat source, which can be electric resistance elements or gas burners, heats up the metal plate. Cookware placed on the plate then heats by conduction from the plate. Since two stages of heat transfer are involved, these units are typically much less efficient than open-top designs. Furthermore, the plate can take 30 to 60 minutes to preheat and cool down. Therefore, chefs typically allow these units to continue operating even during slow cooking periods.
    • French plate element A French plate falls somewhere between the open top and the hot top. The cooking element is a round plate about 6 to 10 inches in diameter. The plate heats up from electric resistance coils or gas burners mounted to the bottom (although most are electric). The plate provides even heat distribution and each "eye" is controlled separately.
    • Induction element The electric induction element is significantly different from other types. Induction coils located under a ceramic surface induce an electric current in the cookware, producing heat. These units offer precise temperature control. These units are by far the most energy efficient because they heat the cookware directly instead of the range surface. The ceramic surface is durable enough to sustain heavy use even when sautŽing.

    Accessories

    Manufacturers offer a variety of optional features for their ranges. Some units are combined with a conventional or convection oven, griddle, or charbroiler. Some provide space for holding cooked food. Some manufacturers offer units with a combination of cooking elements such as hot tops and open tops. Many ranges also have a shelf or a salamander broiler attached to the back of the unit.

    Range operation tips and issues

    Cooking process

    A range cooks food by transferring heat to cookware that in turn transfers heat to the food by conduction. With the exception of induction units, the cookware is heated by an electric resistance coil, a gas or electrically heated solid-top element, or by coming in direct contact with a gas flame. Ranges can use a variety of cookware; but when solid-top elements or resistance coils are used, the bottom of the cookware should be flat to allow good contact with the elements. Rounded bottom pans reduce the amount of heat transferred to the pan.

    Gas open-top units apply a flame directly to the bottom of the cookware. The chef controls the temperature by adjusting the height of the flame, which provides the visual feedback many chefs prefer. Gas units can typically be used with any type of cookware.

    Solid-top units or flat-top units can be heated by electric resistance coils or gas burners. While these units take several minutes to preheat, they provide a very uniform temperature across the surface of the plate. Heat from the plate transfers to the cookware by conduction. Solid-top gas units are much less efficient than their open top counterparts because the plate must heat up before transferring heat to the cookware. Also, with greater preheat time, these units are typically left on while other types of units can be turned off when not needed.

    Performance

    Cooking on a range can be more art than science. An experienced chef has the finesse to get the best performance out of a range. For this reason, less experienced food service operators have difficulty producing consistent food product quality. There is no substitute for trial and error in learning how to adjust temperatures properly. In most cases, it's also important that cookware have a flat bottom to make good contact with the hot top or electric resistance coils.


    Steamers

    Highly efficient, minimal cost of operation, watersavings, minimal maintenance cost.

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    Steamers are used to cook vegetables, seafood, and other foods where moisture retention is essential to appearance and taste.

    Steam cooks food much faster than hot air, improving productivity. Steaming also reduces shrinkage, increasing profits. Steam equipment is relatively easy to use, even for inexperienced operators. Many models include programmable controls that remove guesswork from the cooking process.

    Steam also preserves the nutritional value of most food. This is becoming more important to today's health-conscious consumers.

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    A combination oven/steamer combines the dry heat of a convection oven with the moist heat of a steamer, and chefs can choose among three different cooking modes. This ability makes this piece of equipment extremely flexible and productive.

    Steamer types

    Four major types of steamers are available: Pressureless Steamers, Convection Steamers, Pressure Steamers, and Combination Oven/Steamers.

    Pressureless steamers

    A pressureless steamer uses steam at normal atmospheric pressure to cook food at a constant temperature, which is about 212°F near sea level. However, this temperature drops as altitude increases, so pressureless steamers operating at high altitudes have longer cooking times due to lower steam temperature.

    A boiler injects steam through the cooking compartment's sides where the steam contacts the food, releasing heat energy as it condenses. A pressureless steamer can cook a variety of foods at the same time with no transfer of flavor between foods. A chef can open the door at any time to stir food or check on cooking progress.

    Pressureless steamers are usually equipped with programmable controls. They are available in countertop or floor units, and some models are also stackable to reduce floor space use.

    Convection steamers

    A convection steamer operates much like a conventional pressureless steamer. However, it provides slightly more uniform temperature distribution by using a fan to circulate the steam and air mixture (similar to the way convection ovens circulate hot air). The convective flow of steam accelerates heat transfer to the food.

    Like a conventional pressureless steamer, a convection steamer can cook multiple foods at once with no flavor transfer between foods.

    Pressure steamers

    A c steamer uses steam supplied under pressure at 5 to 15 pounds psi (per square inch). It is very similar to old pressure cookers, which had the advantage of cooking meats and stews more quickly, and which also tenderized tough grades of meat. Pressure steamers have always been popular in large kitchens, schools and institutions.

    Pressure steamers have a locking door that seals in the steam and holds the higher pressure and higher condensing temperature in the cooking compartment. Because of this, the main disadvantage of a pressure steamer is that a chef can't easily access its contents. The unit must be depressurized before opening, and when it is closed again the unit takes awhile to regain operating pressure.

    Combination oven/steamers

    Combination oven/steamers merge the advantages of a steamer's moist cooking with those of a conventional oven's dry air cooking. These units are often praised for their versatility, because chefs can use the oven mode for baking and roasting during peak traffic times, or they can use the steam mode when extra capacity is needed. However, the unit's ability to cook in the combination mode is its most important quality.

    Combination mode is controlled by a microprocessor, which alternates the unit between steam mode and oven mode. For example, under steam mode, roast beef cooks in about half the time of oven mode, but customers like to see meat "browned." Therefore, the combination unit cooks under steam until the meat is mostly cooked, then automatically switches to oven mode to finish cooking and produce the desired browning effect.

    New steamer technologies

    Steam equipment incorporates relatively simple technology. Most of the improvements come from microprocessor controls. These controls remove much of the guesswork from steamer use through pre-programmed cooking times for specific food products.

    Other models called vacuum units are available that operate at reduced steam pressures. These can cook foods at temperatures below 212°F. Some models are even boiler-less units.

    In addition, manufacturers are always looking for ways to achieve greater energy efficiency out of the gas-fueled boiler. Electric boilers are already highly energy efficient.

    Comparing electric vs. gas steamers

    There are many factors to consider when selecting a steamer: initial cost, food preparation productivity, ease of operation, heat generation in the kitchen, and whether electricity or gas is used as the energy source. However, consider that energy only accounts for 3 to 5 percent of a typical food service establishment's total costs. Therefore, while one fuel may be less expensive in a BTU to BTU comparison, the best choice in cooking equipment is the one that minimizes total operating costs, not just energy costs. Features that reduce labor costs or result in higher food product yield will nearly always outweigh any energy considerations. Make sure that you include all of these factors in any equipment evaluation.

    Therefore, when comparing gas and electric models, compare equipment that is similar in all ways except the energy source.

    Advantages of electric steamers

    In general, electric steamers offer these advantages:

    • Electric units are more efficient, adding less heat to the kitchen which ultimately must be removed by the cooling system.
    • Electric units require less maintenance and ventilation, and are more portable.
    • Energy and Money Saving Tips

    Here are a few common-sense operating tips that save money:

    • Steamers preheat relatively quickly because of steam's high heat transfer. The units are usually well insulated to reduce heat loss to the kitchen and to require less energy to maintain temperature during slow times. However, if using multiple steamers during peak times, turn one unit off after the peak cooking cycle.
    • Try to keep each steamer unit fully loaded when possible. The steamer operates at peak efficiency and productivity at full load.
    • One key to efficient steamer operation is controlling water quality. If water in your area is "hard" or contains significant levels of chemicals, the compounds in the water can coat and corrode the steaming components. Such scale and chemical carryover can deteriorate steamer performance and food quality, and almost always results in premature steamer component failures. Always check with a professional water treatment company about proper water softening for your steamers.
    • Keep each steamer unit properly maintained; a clean and well maintained unit operates more efficiently and reduces repair costs. Check that the door seals properly so steam doesn't escape into the kitchen. Also ensure that the boiler is clean, burners or heating elements function properly, and steam injectors are free of debris.

    Steamer components

    All steamers have a cooking compartment that looks much like the inside of an oven. Some units have more than one compartment. Each compartment typically holds about 3 full size steam pans, but sizes vary by manufacturer. The cooking compartment is usually made of stainless steel to make it easy to clean and resistant to corrosion. A drain in the bottom of the cooking compartment drains off any excess water that condenses inside the unit.

    Pressureless steamers have a door that simply latches in place, and the units may be opened and closed during the cooking cycle. Pressure steamers are equipped with a door that locks tightly to hold pressure and prevent steam leakage. These units generally should not be opened during cooking, since they will emit a burst of steam through the opened door, much like the first burst of steam from a boiling pot of water. Obviously, this is hazardous to kitchen workers.

    Steam can be provided from a boiler built into the unit or from an outside source. Built-in boilers use gas or electric energy to heat water, similar to any other boiler unit. Steam flows into the cooking compartment through small holes or jets that are usually located on one side of the cooking compartment.

    Many units also use a set of condenser coils located opposite the steam jets to capture excess steam. They condense the steam back into liquid water and drain it out the bottom of the unit. This prevents tastes from transferring between foods.

    The convection steamer has a fan inside the cooking compartment which circulates the steam/air mixture, increasing air movement and heat transfer to the food. The convection steamer therefore cooks food slightly faster than a conventional unit.

    Steamer operation tips and issues

    Cooking process

    Steamers look and operate much like ovens. An electric or gas boiler creates the steam, which is injected into the cooking compartment. Steam is a much quicker heat transfer medium than hot air. For example, a full size turkey that takes hours to cook in a conventional hot air oven will cook in minutes in a steamer.

    Steam energy is transferred to the food at lower temperatures than hot-air cooking, reducing the chance of overcooking foods. For example, steamers operate at temperatures of 212° to 240°F, while a typical hot-air oven operates between 350° and 450°F.

    However, cooking at this lower temperature does not brown food as well as a hot-air oven. For this reason, chefs often use a steamer to cook food almost to completion, and then transfer the food to a conventional oven for a short period of time for surface browning. They can also accomplish this using a combination oven/steamer, which is designed to do both steam and hot-air cooking.

    Performance

    Steamer cooking performance depends on food product cooking time and the output capacity of the steam generator. Cooking food for the proper amount of time within the capabilities of the steam generator results in consistent quality, portion after portion.

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    Many new steamers have programmable controls to maintain consistent cooking time and steam volume inside the unit. Food service operators simply set the amount of time a dish must cook. The programmable controls also permit a chef to pre-program cooking times so less experienced employees can simply choose the food item from a menu on the control panel.


    Dishwashing

    Efficient, No fumes, Low operational costs.

    One of the single most important food service functions that creates a strong customer image (positive or negative) is the visible cleanliness of dishes, glassware, and silverware. The proper design, operation, and maintenance of this dish washing or ware washing capability is essential to the financial performance of commercial cooking establishments.

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    While the dishwasher is obviously the core of the design, proper dish washing area ventilation is essential to controlling humidity levels for employee comfort, safety and effective ware drying. In addition, adequate lighting enables workers to perform their cleaning tasks more easily. This avoids potentially unsafe situations with broken glass and dinnerware, as well as alerting them to any water accumulation on floors. Finally, adequate electrical power and water pressure are critical to the performance of many dish washing systems.

    A wide variety of dish washing equipment is available on the market. The model that best suits the needs of any one food service establishment largely depends on the menu and the number of meals served. Other factors include:

    • Bussing methods
    • Number of utensils used per table setting
    • Duration and frequency of meal time peaks
    • Waste disposal and pre-washing methods
    • Clean dish storage capacity
    • Organization of dish-room labor
    • Local health codes

    Time management is also paramount, since ineffective dish washing system problems can bring food service operations to a complete halt.

    Finally, dishwashing areas, by their nature, are very noisy. Therefore, special attention should be given to incorporating noise-reducing materials in floors, walls, and ceilings of the dish room. Bussing, scraping, racking, dishwashing, and ware handling noises should be constrained to within the dish room to the extent possible, with special attention towards avoiding disturbing patrons. We will discuss three basic types of dishwashing equipment. They are:
    • Single tank or under-counter
    • Door type
    • Flight and conveyor-rack units.

    Operation

    There are four stages in the proper operation of a dish machine: scraping and pre-wash, wash, rinse, and final rinse/sanitization.

    Pre-wash uses hot water sprays to remove easy grease and soil. Water temperature settings are a compromise between cutting grease and baking on certain foods. Milk, fruit juices, and dairy products are best pre-washed in cold water.

    Wash is the backbone of the cycle where hot water and detergent are pumped through fixed and whirling nozzles above and below the dishes in racks or on conveyer belts. This action loosens and washes away the soil, trapping larger particles for disposal. Water temperature should generally be between 140° and 160°F to soften soils and melt greases. Lipstick removal requires temperatures in excess of 150°F. If the desired water temperature can not be maintained, detergent strength must be increased to compensate.

    Rinse uses 160° to 180°F hot water to remove wash solution and any residual soils. The action is similar to the wash cycle but does not use detergents.

    Final rinse and sanitization removes all traces of the wash solution with water temperatures between 180° and 195°F. These high temperatures have the added advantage of reducing drying times. A rinse additive is injected to facilitate water drainage "sheeting action" and to prevent water spotting during this quick-dry stage.

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    Good dishwashing operation is a compromise between proper cleaning and operating costs. There are obviously tradeoffs between over-washing and under-washing. Water temperature, detergent concentrations, operating cycle times, water pressure, and even rinse additives must all be considered carefully.

    Components

    The basic components of a dishwasher are:

    • The water-holding tank
    • Racks
    • Spray nozzles and blades
    • Controls
    • Door and housing
    • Vents
    • Electrical power and water connections
    • Some units have additional components for special tasks. The most popular special component is the conveyor rack, for enhanced automation.

    Types

    Single tank under-counter dishwasher

    The smallest capacity dishwashing equipment design presently on the market is the single tank or under-counter unit. This model is ideal for smaller establishments such as taverns and bars that generally serve no more than 100 meals a day. The under-counter model washes between 17 and 21 racks of dish-ware per hour and has a maximum water requirement of about 40 gallons per hour. Most under-counter dishwashers operate with a 2-and-one-half minute cleaning cycle. Remember, proper maintenance, adequate ventilation, correct water temperature, and full-load-operation each contribute to overall system efficiency.

    Door type

    Door-type, or stationary rack, machines are one of the most common types of ware-washers because of their compact size and versatility. They are used by small operations with fewer than 150 seats and can wash up to 60 racks of soiled dishes per hour. Door-type dish-washing equipment is best suited for facilities serving 100 to 200 meals a day. The maximum capacity for high temperature machines is roughly 65 gallons per hour. Most machines consume between 70 and 90 gallons of hot water per hour, while low temperature machines average 110 gallons per hour. This type of dishwashing equipment is designed to sit between two tables: a soiled loading table and a clean table on the discharge side of the unit.

    These free-standing door-type dishwashers have a heated tank for storing wash-water at the proper temperature. Water circulates by means of a motor-driven pump through spray pipes or nozzles. These may be located above, below, or both above and below the dish-rack. This unit includes a cover, hood, or door. Fresh hot water from a separate set of nozzles located both above and below the rack provide the final sanitizing rinse. A typical wash cycle lasts about 45 seconds with an additional 12 second rinse cycle.

    Conveyor rack

    Conveyor-rack dishwashers come in one, two, and three-tank models and are capable of washing 125 to 360 racks of soiled dishes per hour. Racks that hold the dishes move on a continuous chain conveyor through each step of the automatic wash and rinse cycle. The operator simply loads the racks and feeds the machine with one rack after another.

    In the lower volume single-tank machine, the tank holds the wash water and detergent mixture. Some of the rinse water, supplied by the booster heater, is then drained into the wash water tank. Double tank machines are designed to hold the wash water while the other tank holds the rinse water permitting much quicker washing cycles. Triple tank machines use another tank for pre-wash cycles to remove food. Blowers and heated dryers are available.

    A two-tank machine has a detergent wash, a hot-water rinse, and a final sanitizing rinse. A three-tank machine includes a pre-wash cycle, eliminating the need to spray-rinse flat tableware manually. These machines are best suited for use in large capacity facilities, such as hotels, hospitals, colleges, and anywhere that 200 to 400 meals are served daily. The typical cleaning cycle lasts one minute, and, on average, these machines use about 415 gallons of water per hour. These figures vary by manufacturer, of course.

    Flight type machines

    Flight-type machines are also called "rackless" or "belt conveyers" and are the monsters of the dish room, capable of washing as many as 24,000 dishes per hour. They are the primary choice for large institutions.

    They come in double, triple, and sometimes custom-built four-tank units. Double tank models are preferred for schools and similar facilities where the food is simple and the variety is limited. The two-tank machine consists of a wash tank and rinse tank. Three-tank models have tanks for prewash, wash, and rinse cycles. All flight type machines have a final sanitizing rinse cycle.

    Ventilation for ware-washing equipment

    Dishwashing equipment produces a large amount of steam and heat, which dissipates into the surrounding area, making the kitchen uncomfortable. A mechanical exhaust ventilation device installed directly above the washing machine can help control the level of steam and heat in the kitchen. General whole-room ventilation can also do the job provided it can sufficiently remove steam and excess heat in the kitchen.

    Ironically, excessive ventilation can be detrimental to washing operations because power-rinse and final-rinse cycles require a certain degree of heat. A ventilation system that is too good, so to speak, can eliminate some of the required heat, making the drying processes virtually ineffective. On the other hand, mechanical ventilation tends to reduce the relative humidity of the room, which enhances air-drying processes, and makes the room more comfortable for employees. Make sure that you consider all the factors when choosing a ventilation system.

    Efficiency

    Saving money

    The easiest way to save money with ware-washing equipment is to purchase insulated models with water saver units and then run the unit with full loads. Some machines do have efficiency management features, such as variable cycle controls for smaller loads, but most commercial dishwashing equipment is designed with volume in mind; it operates most efficiently under a full load. Frequent cycling with small wash loads wastes water, energy, and time. While the dishwashing equipment itself is obviously electric, most of the energy used in dish washing is in the form of hot water. Therefore, selecting the method of water heating, be it resistance, heat pump, heat recovery, or gas-fired, is an important related decision. Contact your local utility representatives to assess these options.


    Refrigeration

    Generally easy to operate and highly reliable.

    The growth of the food service industry has led to the development of highly specialized refrigeration equipment for varied needs ranging from food storage to presentation. This equipment is generally easy to operate and highly reliable, but careless operation and lack of maintenance can be quite costly since this equipment typically must run all the time.

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    Refrigerators and freezers operate more hours than any other kitchen equipment. Their energy use depends on their location in the kitchen, food loading and removal practices, and level of periodic maintenance.

    It is usually wise to purchase the most energy-efficient unit available, but there are other important factors to consider, such as convenience and accessibility. Problems in these areas may cost more in the long run than inefficient energy use. In addition, some refrigeration equipment offers heat recovery options that can reduce site water heating requirements. Therefore, when trying to select an appropriate unit, you may want to work with someone having specialized expertise in refrigeration evaluation, such as a technical representative from your energy company.

    Ice machines

    Commercial ice machines are actually small manufacturing plants that use water and electricity to produce cubed or flaked ice. Cube ice is clear and most often used where appearance is important, such as cocktail ice, carbonated beverages, and ice water for table service. Flake ice is used mostly for packing around food containers in self-serve cold food displays and salad bars. However, it is also used for beverages in smaller food service establishments, despite its reduced visual appeal.

    Water purity to the ice machine is important and a water filter should be installed regardless of water conditions. Sizing the ice-making capacity of the machine depends on the type of restaurant and the number of patrons served. It is generally wise to size the storage small enough to force the ice machine to turn off during "off-peak" times by filling the bin.

    Refrigerator types

    There are a wide range of refrigerator types. The most common types are described below.

    Walk-in units

    When a large amount of refrigeration space is needed, a walk-in unit is often the best choice. Walk-in units easily accommodate the bulk storage of refrigerated and frozen foods. They are manufactured in virtually any size or custom design, ranging from as small as 4 by 6 feet to units so large they approximate cold storage warehouses.

    Walk-ins are available for both indoor and outdoor installation. Most are prefabricated, permitting flexible design and allowing manufacturers to meet nearly any special need.

    Most restaurants use walk-ins predominately for bulk cold storage. However, restaurants may also use a portion of this space for pantry items. To accommodate this need, a popular option for a walk-in unit is one or more glass reach-in doors for easy access, with incidental access to the walk-in refrigerator. This option is considerably more efficient than using a separate small reach-in cooler.

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    The primary access doors for walk-ins come in a wide variety of designs. Traditional hinged doors with safety latches can be replaced with insulated double-swing doors. Some larger walk-in coolers also have sliding or overhead doors to provide clearance for forklifts.

    Larger facilities often use multiple refrigeration units or zones. For example, one unit may be used to store fresh produce at 32° to 36°F, while meats are stored in a separate unit at 34° to 38°F. Dairy products and seafood are often kept in their own separate refrigeration units. However, it is obviously not feasible to have a separate walk-in for every type of product.

    Smaller food service facilities with only one cooler generally operate them at 38°F with a typical freezer temperature kept between 0° and 5° Fahrenheit, or slightly colder if ice cream is stored.

    Reach-in

    Reach-in refrigerators and freezers are used in supplement bulk cold storage equipment. Some restaurants install these in preparation areas next to primary cook stations, in pantries, and in waitress stations. Some very small kitchens may actually use reach-ins for their bulk storage.

    Reach-in units are available with one-, two-, or three-doors, plus half-door models. Doors may open on one side only or from both sides (called pass-through refrigerators). Sliding and glass door designs often have controlled compartments with variable temperature regulation devices. Typical reach-in refrigerators are available in 10 to 75 cubic feet of capacity, and average about 50 cubic feet.

    Reach-in refrigerators and freezers may be mounted on castors for added flexibility or designed to receive roll-in carts or racks. Refrigeration systems for reach-in refrigerators can be self-contained or remote.

    Convenience

    There are three basic types of convenience refrigeration: display cases, base units, and preparation tables.

    Display cases are normally located in the customer traffic areas. They are often equipped with sliding-glass doors and mirrored walls for high product visibility. Display cases are available in numerous shapes and sizes and can be ordered with either sliding or hinged doors. Some have doors at the front and back for easier access. Display cases may be mounted on a wall, a counter, or on the floor with legs or a solid base. Most are constructed of stainless steel and have foamed-in-place insulation.

    Refrigerator and freezer base units offer the convenience of bulk storage at the point of use. Most are floor-mounted and can be installed almost anywhere. These units usually come in one-, two-, and three-door models with optional hinged doors or roll-out drawers. Base units alternately function as workbench surfaces, and can be fitted with special tops to function as preparation-table bases.

    Preparation tables are specially designed to be mounted on top of refrigerated base units. These prep tables include deep removable stainless steel pans that can be used for such items as sandwich or salad fixings and pizza toppings. Most of these pans have hinged lids. The units are mounted to the back of the base unit, providing a work surface for food preparation.

    Energy and money saving tips

    Here are a few common-sense operating tips that save money with a refrigerator.

    • Carefully review and compare manufacturer's stated energy efficiency and estimated operating costs before purchasing equipment. However, note that frost-free versions, although generally less energy efficient, may be cheaper overall to use given the added labor and operational nuisance of manual defrost units.
    • Locate refrigeration equipment away from kitchen heat sources.
    • Open doors as infrequently as possible and close doors promptly after each use.
    • Don't store food at temperatures colder than necessary.
    • Whenever possible, allow cooked food to cool to near room temperature before putting it in a refrigerator.
    • Keep the space near the condenser clear to allow open air flow. Also , periodically check and clean condenser coils to remove dirt and grease buildup.

    Refrigerator components

    The principle components of a refrigeration device are the evaporator, compressor, condenser, expansion device, door and hatch gaskets, and an insulated enclosure. The refrigeration cycle uses the evaporator to produce the cooling or freezing effect. The evaporator coil may have a fan blowing air over it or may simply cool the walls of the refrigerated area. Frost-free devices periodically heat these evaporator coils to melt off the ice and frost that naturally forms on freezing surfaces.

    The evaporator boils a fluid (called a refrigerant) at a relatively low temperature to remove heat from the refrigerated area. The resulting refrigerant vapors are fed into a compressor that raises the pressure enough to condense (that is, re-liquefy) the vapors in the component called the condenser, which also removes heat. On some systems, the heat removed by the condenser is trapped and used for site water heating or defrosting. However, in most systems this removed heat is either released into the kitchen (in small cooling equipment) or to outdoor condenser coils. Most condensers are cooled with fans, just like a home air conditioner or heat pump, but in some locations condensers can also be cooled with cooling towers or ground water.

    The expansion device controls the flow of refrigerant by maintaining the proper pressure difference (called head) between the condenser and the evaporator. Older, inefficient refrigeration units had relatively simple expansion devices. Many newer "floating head" refrigeration designs use microprocessor- based controls to increase energy efficiency.

    Optimal storage temperatures by food type

    A food service facility's menu determines the types of foods that must be stored, which largely establishes the cooling requirements for a kitchen's refrigeration units. The table below lists approximate storage temperatures for several main food categories:

    Frozen foods -20° to 0°F
    Ice cream -15° to +15°F
    Fish and shellfish 23° to 30°F
    Meat and poultry 30° to 38°F
    Dairy products 38° to 46°F
    Fruits and vegetables 44° to 50°F

    Ventilation Systems

    Wide range of systems designed to meet different needs.

    In general, building ventilation systems must bring in enough fresh air for occupant comfort, while also controlling indoor temperature, humidity, and air quality to ensure personnel and building safety. All of this must be accomplished at reasonable energy costs. Food service kitchen ventilation systems have the additional burden of removing the grease vapors, odors, moisture, smoke and heat generated by cooking. This is essential to a safe, comfortable, and productive kitchen environment. Fire protection is also an essential element in food service ventilation design.

    The design of kitchen and other food service ventilation systems requires a professional, and it should not be attempted by unqualified persons using the guidelines and general comments offered here. The intent of this information is only to familiarize you with ventilation design considerations and typical equipment solutions.

    The creation of grease vapors, odors, moisture, products of combustion, and smoke is generally focused in specific kitchen areas and varies based on the equipment used. The common solution is to vent, capture, and possibly eliminate contaminants through carefully designed hoods with adequate venting flow rates and fresh air makeup. Simply oversizing the vent system is not a proper approach and can be very costly in energy bills. A successful and economical design requires careful consideration of cooking equipment selections, cooking equipment arrangement and coordination in the kitchen, and appropriate vent-hood design.

    Heating, ventilating, and air conditioning (HVAC) costs are significant in most food service businesses. Furthermore, failure of the HVAC system in the kitchen is reflected in worker productivity and possibly in worker turnover. HVAC system design requirements in the dining areas are simpler, but must consider both customer comfort and economical building operation.

    In addition, the HVAC design must consider the way space is operated and maintained. If the space is a commercial kitchen in a much larger building, like a hospital cafeteria, energy systems are probably maintained by a professional staff. In these cases, system options can be reasonably sophisticated. On the other hand, if a food service establishment is an isolated small building, like a fast food restaurant, the staff are probably only going to operate systems by pressing simple start and stop buttons, so the HVAC systems should not be difficult to maintain or operate. These are probably not situations where more elaborate and complicated systems should be considered.

    Types of ventilation systems

    There are a wide range of food service ventilation systems designed to meet different ventilation requirements. The most common types are described below.

    Back-shelf ventilators

    A back-shelf ventilator is the best alternative in kitchens where low ceiling height or a lack of space prevents use of an overhead canopy. The unit is installed at the rear of the cooking equipment, closer to the actual cooking surface than an overhead canopy. Back-shelf units are not intended for heavy production usage, nor for use with high-exhaust-surge cooking equipment like char-broilers.

    The typical minimum clearance (distance between the cooking surface and filters) is 18 to 25 inches. This distance prevents overheating that can cause accumulated deposits to bake on the vent filters. Excessive temperatures also tend to vaporize grease, which allows it to pass through the filter and deposit on internal system components. This increases cleaning and maintenance costs.

    The hood of the back-shelf ventilator should extend from the wall a distance of at least 24 inches, but be set back enough from the front to allow adequate head clearance for cooks. Cooking equipment should extend no more than 36 inches.

    Canopy hoods

    Canopy hoods are installed either against a wall or above cooking equipment (called island canopies). The length and width of the hood face should equal the total dimensions of the cooking appliance plus an appropriate overhang on each side. This overhang amount depends on the hood style and the kitchen appliance used.

    A wall canopy with side curtains is possibly the most efficient design for capturing contaminated air. An island canopy hood is the largest type but is quite susceptible to cross-drafts and air spillage. Side air curtains prevent cross-drafts. Also, back paneling or tempered glass may be installed to produce a rear wall effect.

    Eyebrow hoods

    Eyebrow style hoods are mounted directly to ovens and dishwashers to catch effluents. This hood type can be designed to operate only when appliance doors are opened or at certain points in the cycle.

    Pass-Over hoods

    The pass-over hood configuration is used over counter-height equipment where a pass-over capability is required. That is, prepared food is passed over from the cooking surfaces to the serving side.

    Make-up air

    Introducing make-up air into a kitchen to produce a completely comfortable environment is very difficult. Achieving uniform comfortable temperatures, odor control, gentle air circulation, and minimal aggravating updrafts requires careful design and placement of wall registers, ceiling diffusers, and slotted ceiling panels.

    Kitchen exhausts should be located away from the HVAC fresh air intake. If an existing HVAC system draws in odor-saturated exhaust, a baffle or barriers should be erected between the roof exhaust and the fresh air intake. These are just some of the reasons why kitchen design should be reserved for qualified professionals.

    Wall registers are installed close to the ceiling, projecting return air across the ceiling in a straight line. The make-up air mixes with current air, circulating into the occupied zone. Problems often arise with wall registers because their high velocity operation may create additional updrafts.

    Ceiling diffusers are normally flush mounted in the ceiling panels. These discharge supply air in a circular motion, outward along the ceiling. Where wall canopies are used, ceiling diffusers operate exceptionally well, if located a "sufficient distance" from all appliances and hoods ("sufficient distance" is defined as the equivalent of the maximum throw distance listed for the diffuser). When an island hood is used, it is difficult to apply a ceiling diffuser in a manner that effectively avoids updrafts.

    Slotted ceiling panels provide a gentle uniform distribution of make-up air. Ideally, discharge air from ceiling slots should penetrate to face level at the rate of 20 to 25 feet-per-minute. In a properly designed system, return make-up air should barely affect the overall ventilation process.

    Pollution control devices

    Many local environmental ordinances require installation of pollution control devices with kitchen exhaust systems, especially where char-broilers or other smoke generating cooking equipment is used. Two devices commonly implemented for "pollution control" are electrostatic precipitators and fume afterburners. Both are installed within the exhaust system and are essential in reducing air pollution.

    Heat recovery devices

    Heat recovery devices are becoming more common. These devices are usually designed to recover and recycle energy for space heating and water heating. Without recovery units, this energy would be wasted.

    All energy recovery systems operate on the same principle. Energy is recovered from outgoing air exhaust using a wheel, coil, pipe, or other device. The recovered energy is transferred to incoming air or water. Air-to-air heat recovery systems rely on the fact that air leaving the kitchen is hotter than incoming fresh air for most of the year. In this design situation, incoming air is warmed. Where the air leaving the kitchen is colder than outside air, it is cooled. This reduces the load on the primary heating and cooling system, reducing energy costs.

    Another common energy recovery system captures waste heat from on-site refrigeration units or kitchen exhausts to produce hot water. Such a system is called a heat pump system and is available either as an option in the refrigeration system or as an add-on spot cooling system. Spot cooling systems are commonly specified for kitchens with inadequate cooling and are sold on the basis that they provide economical cooling and "free" hot water.

    There are also many other types of heat recovery devices on the market including rotary or "heat wheel" regenerators, air-to-air plate-type exchangers, heat pipes, and liquid "run-around" coils. Predicting the cost performance of these systems and properly implementing them into a kitchen HVAC design is work for a professional and should not be based on advertising or equipment supplier claims. All of these designs have proven cost effective in certain situations when properly incorporated into the overall kitchen design. However, all of these designs have also failed when not properly integrated into the kitchen design.

    Hoods: operation & specification issues

    Most people have experience with ventilating hoods in their home kitchen and recognize the need for the hood to control smoke and fumes that might otherwise create discomfort. The hood needs to be designed for three key factors:

    • the location of the food preparation device emitting the smoke and fumes to be vented
    • the thermal updraft that forms above the surface of operating cooking equipment
    • the resultant inrush of air to replaces this rising air flow

    The location of cooking equipment relative to the ventilation hood greatly impacts the system's effectiveness. Cooking equipment is commonly installed so the rear faces the wall. Since the heated surface is only minimally exposed to open air, the inrush created by the heat vacuum is greater at the front edge of the appliance, and modern hoods are designed to use this added updraft.

    The hood must have enough capacity to capture and exhaust contaminated air from the kitchen. Surges of contaminated air in excess of this capability may cause "spill" out of the hood and can create unpleasant, uncomfortable, and even unsafe conditions. Also, the use of gas-fired cooking equipment may need additional allowances for the exhaust of combustion products and combustion air. Therefore, proper hood size should be specified to reflect the actual cooking equipment and the cooking duty required. These hood design criteria include an overhang requirement and a minimum exhaust flow rate, expressed in cfm (cubic feet per minute) per linear foot of hood.

    Kitchen hoods are designed for specific cooking situations and are broken into two broad categories: Type I and Type II. Type I hoods are used for the collection and removal of grease and smoke. Type II hoods are general duty hoods for the collection and removal of steam and water vapors, heat, and odors where grease is not present.

    Ventilation maintenance issues

    HVAC systems are a significant part of energy costs for most food service operations. The single most cost effective way to reduce these costs is to ensure that energy systems are operating properly. However, building systems are often unintentionally defeated when occupants complain about being hot or cold. For example, complaints about being cold during the hottest days of the year may cause adjustments to be made in setpoints for the system. When the weather later changes, the setpoints are probably not reset to a more economical setting. Furthermore, checking for a system problem that caused the discomfort in the first place is rarely done.

    When breakdowns occur, there is a natural tendency to quickly patch the system back into operation instead of looking at improper system operation as part of the cause for the system failure. For example, an important routine maintenance item is changing filters and cleaning external components. Most buildings are operated such that these tasks are done only when their neglect causes a problem. However, a clogged filter puts unnecessary strain on the HVAC system fans and heating and cooling system, and consequently raises energy costs. It also usually creates occupant discomfort.

    The volume and type of food cooked in the kitchen determines how frequently an exhaust system needs cleaning and maintenance. Select an appropriate schedule for HVAC maintenance by monitoring the rate of build-up in the exhaust filters and duct access doors for a least a month. This should provide enough information for specialists to suggest an ideal schedule for system cleaning and repair. Many professional building operators also put a pressure drop indicator on filters to indicate when they need maintenance.

    Another key way of reducing system operating and maintenance costs is to educate site personnel in proper HVAC operation. Turning systems off at appropriate times, setting thermostats, and even simple things like closing doors can create significant annual savings and increased equipment life. However, major equipment maintenance tasks should be left to professional maintenance contractors.

    Ventilation components

    Commercial kitchen heating, ventilating, and air conditioning systems are similar to standard building designs except for make-up air systems and hoods. Make-up air systems include wall registers, ceiling diffusers, and slotted ceiling panels. Kitchen hoods are designed for specific cooking situations and are divided into two broad categories: Type I and Type II.

    Type I hoods are used for the collection and removal of grease and smoke. They always include filters or baffles for grease removal and are normally required over fryers, ranges, griddles, broilers, ovens, and steam jacketed kettles.

    Type II hoods are general-duty hoods for the collection and removal of steam and water vapors, heat, and odors where grease is not present. Therefore, these units may not have grease filters or baffles. They are typically used over dishwashers, steam tables, and similar equipment. However, they may also be specified for use over other equipment when allowed by local codes and authorities. Always check with a design professional for these rulings.

    Case studies

    For more information about the benefits of ventilation systems, please contact us for a copy of an EPRI performance or ventilation report.


    Whether retrofitting an existing dehumidification system, or installing a new one, technology exists to control humidity, improve indoor air quality, reduce bacterial growth, or prevent sick-building syndrome. Other considerations include installation costs, energy costs, available space or maintenance and service needs. This page provides summarized descriptions of numerous dehumidification systems.



    Improved Single Path

    A method which increases cooling efficiency by lowering in-store humidity, especially suited for supermarkets and super-stores.

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    While conventional system designs can be used, they are not designed to produce the optimum humidity conditions needed in applications such as supermarkets and super-stores, as outdoor air is mixed with return air and then cooled and dehumidified. When forced to control humidity, their energy performance is usually poor, as they are typically run to cool all the air to a lower temperature to remove moisture. This supply air is then reheated, often using refrigeration waste heat reclaim, to avoid overcooling the store. Lower in-store humidity (about 40%) made possible by specialized air conditioning systems means lower refrigeration energy costs. Reduced humidity directly reduces this energy use by reducing frosting and thus enhances coil heat transfer. To better handle these issues, special equipment is often considered, including:

    • Improved single path electric system,
    • Dual path electric system (discussed in a separate segment) which combines a separate ventilation and return air path in a single unit.

    Advantages

    The improved single path system:

    • Offers reduced supply air volume, bypass, and high efficiency air handler motors that provide reduced air handler demand and energy charges throughout the year,
    • Substantially increases dehumidification performance,
    • Reduces or eliminates reheat requirements
    • Has maintenance costs proportionately lower than conventional systems due to the equipment capacity reduction,
    • Achieves both low first cost and simplicity,

    Disadvantages

    The dehumidification characteristics may not match modern supermarket loads exactly.

    Applications

    Single path systems can be used in both retrofit and new installations, separately or integrated with additional HVAC or refrigeration equipment. They are currently available in factory packaged units for indoor and outdoor installation.

    Best applications

    • Their excellent operating performance and design simplicity make them a natural choice for supermarket designers and operators looking for a proven and reliable technology with no special maintenance requirements,
    • HVAC applications requiring good control of outdoor air quantity and humidity control of supply air,
    • They are a good choice for replacing conventional rooftop units being retired.

    Possible applications

    • Schools, stores, restaurants, commercial office and other buildings where humidity is a concern and old CFC-using or inefficient equipment must be replaced.
    • Process or industrial applications requiring good humidity control of supply air.

    Technology types (resource)

    The features that distinguish improved single path systems from conventional systems include:

  • A mixture of fresh and return air is cooled by lower evaporator temperatures for better dehumidification; coil leaving air temperature of about 40 to 45°F compared to 52 to 56°F in conventional systems,
  • Reduced total supply air volume, as low as 0.5 to 0.7 cfm per sq ft of sales area, compared to about 1.0 cfm per sq ft for conventional systems,
  • Partial evaporator air bypass allows the air treated by the evaporator to be cooled to a lower temperature, increasing moisture removal and reducing or eliminating reheat requirements,
  • The cooled and bypassed air is remixed before the heat recovery and heating coil and before delivery to the space. This bypass design also permits a smaller compressor since the lower airflow compensates for the larger temperature drop through the coil. Using bypassed air also lowers reheat energy needs, while the smaller ducts and power wiring reduces first cost,
  • Use of high efficiency air handler motors can reduce air handling energy by 10% or more,
  • Careful sizing to avoid excess capacity,
  • Improved part load controls with face-split cooling coils that permit a portion of the coil to be operated at a lower temperature while air is bypassed around the rest of the coil.
  • Efficiency

    A recent EPRI study examined installed costs and energy costs for a variety of supermarket HVAC systems. An improved single path system typically reduced the HVAC installed cost by up to 23% over a conventional single path system. The single path systems typically will reduce the annual operating cost between 9% and 13%. The reductions will depend on the location and the design parameters.

    Other information

    Contact us to receive a copy of an EPRI report on Improved Single-Path HVAC Systems or for more information.

    Links to more detail


    Desiccant Systems

    A cost-effective method for creating low humidity environments, utilizing desiccant material to remove the moisture by absorption or adsorption. Effective in deterring microbials.

    Desiccant systems in HVAC applications, an alternative or supplement to mechanical refrigeration, are used primarily where simultaneous maintenance of temperature and humidity control is an important benefit to the user.

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    Desiccants are defined as materials which attract and hold water vapor. With desiccant systems the sensible and latent functions are separated. A desiccant material is used to remove the moisture by absorption or adsorption. Refrigeration is then used to lower the temperature only to the desired level for distribution. This refrigeration is done at a higher temperature than in a typical conventional HVAC thereby achieving a higher operating COP (lower kW/ton). A reduction in energy costs for air conditioning is possible.

    They can be used to create very low humidity environments (5-10% relative humidity) which would otherwise be difficult and expensive to maintain using compression-refrigeration equipment. Desiccant-based energy recovery systems basically decouple the latent load from the equipment (typically mechanical cooling) handling the sensible load. It is often used on projects where the latent load is in excess of that which can be done by conventional unitary cooling equipment. They are often considered when controlling relative humidity is essential to avoiding the growth of microbials.

    Advantages

    If are properly applied and are correctly designed, desiccant systems can also produce these benefits:

    • Independent control of latent loads in the ventilation air.
    • Eliminate condensation on cooling coils and in drip pans, and reduce humidity levels in ducts. This will virtually eliminate the growth of mold, mildew, and bacteria. The combination can reduce maintenance and help avoid indoor air quality problems.
    • Lower humidity levels in occupied spaces provides equivalent comfort levels at higher ambient temperatures. This could allow chilled water set-points to be raised and there-by save energy and reduce system operating costs.
    • Reduce the mechanical cooling load, permitting the use of smaller chillers and possibly even smaller ducting in new construction. These construction cost offsets should be factored into any economic evaluation.

    Disadvantages

    While there are special design situations where desiccant/evaporative chilling systems are potentially economic, the complication of such systems limits their acceptance, especially in situations where there are limited or no on-site qualified operating personnel. Other disadvantages include:

  • Increased first cost
  • Increased maintenance of the added desiccant equipment
  • Cost of energy (usually natural gas) to regenerate the desiccant at a high temperature to drive off the entrained moisture
  • In some cases, the need for piping of cooling (typically tower) water to remove the heat of adsorption and precool the heated air off the desiccant units
  • Links to more detail

    Applications

    Changes in building construction and use has caused lower sensible cooling loads due to increased insulation, better windows, and more efficient lighting. At the same time, higher ventilation air requirements, together with higher building occupant densities, result in higher dehumidification loads which means higher moisture (latent) loads.

    At the same time the demand for higher efficiency cooling units has manufacturers using larger evaporators operating at higher refrigerant temperatures, resulting in reduced moisture removal ability compared to the sensible capacity...a higher sensible heat ratio of the equipment.

    Conventional systems use refrigeration to provide both sensible (lower the air temperature) and latent (dehumidify the air) cooling. To achieve the lower relative humidity desired in some spaces, the air must be cooled below that needed for the sensible load in order to remove sufficient moisture, and then reheated to prevent over-cooling thus increasing energy use. Desiccant systems, coupled with mechanical cooling, can avoid the need for reheat.

    Desiccant systems have been commonly used for many years in industrial processes where very low humidity is a must. Other applications include maintaining controlled humidity in warehouse and caves used for storage, preserving ships and other such facilities that would otherwise deteriorate due to moisture build-up, drying air to speed drying of heat-sensitive products. The changing conditions and dehumidification requirements have expanded its use in HVAC applications.

    Best applications

    Desiccant systems can be used to create very low humidity environments (5-10% relative humidity) which would otherwise be difficult and expensive to maintain using compression-refrigeration equipment. Pharmaceuticals and others manufacturing hygroscopic products require low humidity operating environments. Candy, seed and photo-film manufacture often require dry air to speed drying of the product. They can be used to retrofit a project where the installed conventional equipment can not maintain the desired humidity levels or where conditions have changed to create a humidity problem (example: original design had too low an outdoor air intake). Heat pipes are often coupled with desiccant systems to improve performance.

    Desiccant systems are potentially best applicable where:

    • Extremely low humidity (less than 30% relative humidity) is required,
    • The latent load is large in comparison with the sensible load,
    • The cost of energy to regenerate the desiccant is low when compared with the cost of chilling the air below its dewpoint.
    • The air would have to be chilled to a subfreezing dewpoint with mechanical refrigeration.
    • The process requires continuous delivery of air at subfreezing temperatures. With desiccant removal of water in the air the defrost problem on the chilling coils is minimized.

    Possible applications

    The changing requirements for increased ventilation air, increasing the latent load, may increase the application for these systems, particularly as on-peak electric costs rise. With low sensible heat ratios, the relative humidity can rise leading to mold, mildew and fungus along with more uncomfortable space conditions. Desiccant cooling is also considered in all-air systems where 100% outside air is required (clean rooms, hospital operating rooms, laboratories and some restaurants), in supermarkets in humid climates and ice rinks.

    Hotels have used desiccant systems to provide dry makeup air to maintain a slight positive pressure in corridors. This minimizes humid outdoor air being pulled into the rooms through windows and exterior walls by the toilet exhaust system. The lower humidity air also reduces mold and mildew damage and cost of replacing furniture and wall coverings.

    In many cases, other alternatives such as ice storage, ventilation air precooling, and dual path units may produce the desired result at a lower first and operating cost.

    Some desiccant system vendors target market these systems to supermarkets and fast food chains. Reciprocating engine driven cogeneration is often included in the design as a way to use engine waste heat in summer. The perceived advantage is that when the supermarket operates at lower humidity (40%, or less) there is a saving on refrigerated food case energy use, due to a reduced need for defrost cycles and to higher efficiency with reduced frost on the evaporator.

    Actual financial performance is still unclear, even those projects reported by the Gas Research Institute. Four systems installed in a fast food chain, which were surveyed in detail, failed to provide any significant savings in electric energy and actually may have increased operating costs. In addition, in some situations, the system parasitics (pumps and fans) were unknowingly paid for by these customers as additional electric charges, thereby further reducing actual operating savings. The choice of an induction generation in the cogeneration system also accelerated the failure of other on-site electric equipment. The greatest savings came from coincident fine tuning of existing HVAC system performance.

    A superior way to improve system performance can probably be obtained through the use of ice-based thermal storage systems to lower air supply humidity and avail the customer of lower cost off-peak power. Other options include supermarket rooftop units with heat reclaim and subcooling, and with dual path units. In addition, heat pipes have been demonstrated to provide superior economic performance in many applications.

    Desiccant units have been used in supermarkets as lower space humidity has been shown to improve the energy performance of case work, increase occupant comfort and may even improve sales. The two key questions are : Which alternative is the most cost effective to install? Which alternative represents the best system to install in a given application? Both of these questions should be addressed by a qualified professional.

    Technology types (resource)

    There are two broad categories — liquid and solid desiccant systems.

    Liquid desiccant systems use spray air washer type equipment with remote regeneration. They are typically used for large applied industrial applications.

    Solid, inorganic, crystalline desiccants are impregnated in inert materials and used in a unit with a honeycomb type heat-wheel. They are typically used for commercial HVAC applications.

    Solid desiccant systems are available in single-wheel and dual-wheel factory packaged units. The single wheel units include a desiccant wheel, cooling coil and reheat coil (hot gas, electric, steam, hot water, etc.). Outdoor air is dehumidified by the desiccant wheel, a cooling coil reduces the air temperature to the desired dew point and the reheat coil raises the air to the desired dry bulb temperature.

    The dual-wheel units use a desiccant-based wheel and a sensible-only heat wheel along with the conventional chilled water or direct expansion coil. During the cooling mode the sensible-only wheel is used as a post-cooler (partially cool hot dry air off the desiccant wheel while preheating regeneration air) or to reheat the over-cooled dehumidified air.

    Heat is required to regenerate or reactivate the desiccant material (drive off the absorbed water vapor and discharge it outdoors using a scavenger air stream). Part of the wheel is exposed to the conditioned or process air and the balance to the reactivation air stream. Natural gas is usually used to provide the heat for regeneration in single wheel units; a combination of exhaust air and gas heat may be used on dual-wheel systems.

    In addition to the supply air fan, desiccant units require

    • a process air fan to pull air through the wheel and over the cooling coil,
    • a reactivation air fan
    • a fractional hp motor to rotate the wheel
    • in some cased, a fractional hp motor driving an inducer fan to push flue gases outdoors.

    Efficiency

    The combination of desiccant dehumidification and mechanical cooling can allow the chilled water or direct expansion system to operate at a higher evaporator temperature and thus a higher efficiency and reduce operating costs. The amount will depend on site requirements.

    Desiccant units typically remove about 4 to 8 pounds or more of moisture per hour for each 1,000 cfm of circulated air. The lower the air flow face velocity through the desiccant and the higher the inlet air humidity the more the moisture that is removed. The addition of a dual wheel reduces the amount of mechanical cooling and reactivation heat required.

    While desiccant equipment is durable and efficient where properly applied, it does require special maintenance. Good filtering of both air streams (incoming and outgoing) is vital. The filtering system must be clearly visible to maintenance personnel, it must be easily inspected, removed and replaced, and a maintenance schedule must be established and followed. If a solid desiccant is clogged with particulate or a liquid desiccant properties are changed by entrained particulates, its efficiency drops rapidly and it may have to be prematurely replaced.

    The wheel(s) and their rotating mechanisms must be clearly visible to maintenance personnel, they must be easily inspected, maintained and repaired. Care must be taken to not allow holes to be drilled in the casings, access doors to become warped, etc. as if humid air leaks into either the dry air ductwork or into the unit itself, the system efficiency is markedly reduced. The life expectancy of the wheel is also dependent on the proper operation of the regeneration system.

    Other information

    Contact us for a detailed list of manufacturers for this equipment.

    Links to related and similar


    Electric Desiccant Heat Pumps

    These systems use a combination of an electric vapor compression cycle as well as desiccant material. Desiccant material is regenerated from the waste condenser heat off of the vapor compression cycle.

    Electric desiccant heat pumps can offer an effective means of controlling space humidity. These systems use a combination of an electric vapor compression cycle as well as desiccant material, and where desiccant material is regenerated from the waste condenser heat off of the vapor compression cycle (similar to heat pump water heaters).

    Desiccant systems in HVAC applications, an alternative or supplement to traditional air conditioning systems, are used primarily where the latent load is high or where independent control of temperature and humidity is an important factor.

    Desiccants are materials which attract and hold water vapor at room temperatures and regenerate at high temperatures. The traditional lithium chloride and silica gel desiccant materials require a minimum of 180°F regeneration temperature. Where as, the new Engelhard/ICC patented zeolite desiccant material which is used in this new product line can be regenerated at very low temperatures of 120 to 140°F heat. This new feature allowed the desiccant material to regenerate using the condenser waste heat off of the air conditioning refrigerant loop.

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    From 1994 to 1997, Southern Company was actively involved in the development, evaluation, and demonstration of this product.

    Advantages

    • Supplies make-up/ventilation air with higher efficiency, cost-effectively meeting increased ventilation loads per ASHRAE 62-89.
    • Can be integrated easily with existing conventional HVAC equipment; solving make-up air problems that conventional equipment can't handle.
    • Eliminates/minimizes expensive over-cooling and reheat required to dehumidify as with conventional equipment.
    • Permits independent control of humidity and temperatures control for improved comfort and control of space conditions.
    • Lower humidity levels in occupied spaces provides equivalent comfort levels at higher ambient temperatures.

    Disadvantages

    • Relatively higher unit and installation costs.
    • Units are relatively bulky. May require careful roof structure evaluation for roof-top installations.
    • Requires periodic (once a year or so) service/maintenance check up due to additional rotating parts.desiccant wheel, belt drives, evaporator pad, etc.
    • Limited manufacturers and lack of enough trained technician network

    Best applications

    Desiccants are very efficient for treating 100% make-up/ventilation air. Some of the applications include:

    1. Existing building requiring higher ventilation air either to meet ASHRAE 62-89 ventilation air requirements or increased human occupancy. Desiccant systems can be installed to treat just the make-up air portion and the outlet air from these units can be tied to return air of existing HVAC equipment. This will have the potential for minimizing/eliminating the need for major retrofitting of existing systems.
    2. In new construction, desiccant can be easily integrated with conventional HVAC designs. Desiccants can be designed to treat ventilation air portion, thereby reducing the latent load on conventional HVAC equipment. This approach will likely reduce overall energy consumption and demand. May permit the downsizing of conventional system by separating latent and sensible loads.
    3. Some the commercial applications of this type application may include schools, auditoriums, theaters, low-rise office buildings, supermarkets, restaurants, etc.
    4. Desiccant systems are also well suitable for any facility where humidity control is required or the ratio of latent to sensible load is very high. A few examples of this type of applications include:

    5. Supermarkets ---- eliminating frost build up on frozen foods, freezer case coils, and freezer case doors; reducing sweat on refrigerant cases and greatly reducing anti-sweat heater operation; and maintaining a more comfortable environment.
    6. Hospitals --- providing flexible temperature and humidity control for operating rooms; minimizing spores and bacteria, which cause microbiological growth.
    7. Ice rinks --- improving the quality of the ice by eliminating crystal formation on the skating surface, thus extending the operating season and revenue; preventing rust and mildew, and the formation of fog over the ice; extending the life of the facilities and operating equipment.
    8. Warehouse --- places requiring just the humidity control and not necessarily temperature control.

    Possible applications

  • Offices and retail stores --- helping to eliminate "sick building syndrome" by lowering relative humidity and thereby improving indoor air quality.
  • Museums, libraries, hotels, health spas, --- eliminating mold and mildew problems, along with musty odors especially in the coastal areas; extend the life of archives.
  • Technology types (resource)

    Engelhard/ICC is the only company offering these hybrid electric desiccants. They are now available in two options:

    1. 100% ventilation air systems: These units are designed to treat up to 100% of fresh air. The treated air from these units can be either supplied directly into the space or can be used as a make-up air (treating outside air portion) for conventional air conditioning units. These units are designed to remove approximately 70% latent and 30% sensible load from the outside air at rated 95°F DB and 78°F WB conditions. If the exhaust air from the space is used for regeneration, the efficiency of the unit will increase by about 10%. These units are available in the sizes ranging from 1,600 cfm to 5,000 cfm.
    2. Heat reclaim systems: These units are available in various sizes from 1,000 to 20,000 cfm and they are especially designed for supermarket application. They are designed to utilizes heat reclaimed from the store's refrigeration compressors to regenerate the desiccant materials as opposed to using air conditioner condenser heat. These units can deliver warm, dry air directly to the frozen food aisles, there by keeping relatively humidity levels near freezer aisles. When the store requires sensible cooling, cool air circulated from the conventional air conditioner will be redirected away from the frozen food section and towards the front of the store, where it is most needed.

    Contact us for a detailed list of manufacturers for this equipment.


    Heat Pipes

    This space-saving, passive energy recovery heat exchanger can enhance latent heat transfer and improve efficiency.

    A heat pipe is a passive energy recovery heat exchanger that has the appearance of a common plate-finned water coil except the tubes are not interconnected. Additionally it is divided into two sections by a sealed partition. Hot air passes through one side (evaporator) and is cooled while cooler air passes through the other side (condenser). While heat pipes are sensible heat transfer exchangers, if the air conditions are such that condensation forms on the fins there can be some latent heat transfer and improved efficiency.

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    Heat pipes are tubes that have a capillary wick inside running the length of the tube, are evacuated and then filled with a refrigerant as the working fluid, and are permanently sealed. The working fluid is selected to meet the desired temperature conditions and is usually a Class I refrigerant. Fins are similar to conventional coils - corrugated plate, plain plate, spiral design. Tube and fin spacing are selected for appropriate pressure drop at design face velocity. HVAC systems typically use copper heat pipes with aluminum fins; other materials are available.

    Advantages

    • passive heat exchange with no moving parts,
    • relatively space efficient,
    • the cooling or heating equipment size can be reduced in some cases,
    • the moisture removal capacity of existing cooling equipment can be improved,
    • no cross-contamination between air streams.

    Disadvantages

    The use of the heat pipe

    • adds to the first cost and to the fan power to overcome its resistance,
    • requires that the two air streams be adjacent to each other,
    • requires that the air streams must be relatively clean and may require filtration.

    Applications

    Heat pipe heat exchanger enhancement can improve system latent capacity. For example, a 1°F dry bulb drop in air entering a cooling coil can increase the latent capacity by about 3%. Both cooling and reheating energy is saved by the heat pipe's transfer of heat directly from the entering air to the low-temperature air leaving the cooling coil. It can also be used to precool or preheat incoming outdoor air with exhaust air from the conditioned spaces.

    Best applications

    • Where lower relative humidity is an advantage for comfort or process reasons, the use of a heat pipe can help. A heat pipe used between the warm air entering the cooling coil and the cool air leaving the coil transfers sensible heat to the cold exiting air, thereby reducing or even eliminating the reheat needs. Also the heat pipe precools the air before it reaches the cooling coil, increasing the latent capacity and possibly lowering the system cooling energy use.
    • Projects that require a large percentage of outdoor air and has the exhaust air duct in close proximity to the intake, can increase system efficiency by transferring heat in the exhaust to either precool or preheat the incoming air.

    Possible applications

  • Use of a dry heat pipe coupled with a heat pump in humid climate areas.
  • Heat pipe heat exchanger enhancement used with a single-path or dual-path system in a supermarket application.
  • Existing buildings where codes require it or they have "sick building" syndrome and the amount of outdoor air intake must be increased,
  • New buildings where the required amount of ventilation air causes excess loads or where the desired equipment does not have sufficient latent capacity.
  • Technology types (resource)

    Hot air is the heat source, flows over the evaporator side, is cooled, and evaporates the working fluid. Cooler air is the heat sink, flows over the condenser side, is heated, and condenses the working fluid. Vapor pressure difference drives the evaporated vapor to the condenser end and the condensed liquid is wicked back to the evaporator by capillary action. Performance is affected by the orientation from horizontal. Operating the heat pipe on a slope with the hot (evaporator) end below horizontal improves the liquid flow back to the evaporator. Heat pipes can be applied in parallel or series.

    Efficiency

    Heat pipes are typically applied with air face velocities in the 450 to 550 feet per minute range, with 4 to 8 rows deep and 14 fins per inch and have an effectiveness of 45% to 65%. For example, if entering air at 77°F is cooled by the heat pipe evaporator to 70°F and the air off the cooling coil is reheated from 55°F to 65°F by the condenser section, the effectiveness is 45 % [=(65-55)/(77-55) = 45%]. As the number of rows increases, effectiveness increases but at a declining rate. For example, doubling the rows of a 48% effective heat pipe increases the effectiveness to 65%.

    Tilt control can be used to:

    • change operation for seasonal changeover,
    • modulate capacity to prevent overheating or overcooling of supply air,
    • decrease effectiveness to prevent frost formation at low outdoor air temperatures.

    Tilt control (6° maximum) involves pivoting the exchanger about its base at the center with a temperature-actuated tilt controller at one end. Face and bypass dampers can also be used.

    Contact us for a detailed list of manufacturers for this equipment.


    Dual Path Systems

    A system which increases humidity control and reduces bacteria growth; especially suited for supermarkets and super-stores.

    While conventional system designs can be used, they are not designed to produce the optimum humidity conditions needed in applications such as supermarkets and super-stores, as outdoor air is mixed with return air and then cooled and dehumidified. When forced to control humidity, their energy performance is usually poor, as they are typically run to cool all the air to a lower temperature to remove moisture. This supply air is then reheated, often using refrigeration waste heat reclaim, to avoid overcooling the store.

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    To better handle these issues, special equipment is often considered, including:

  • Improved single path electric system, with a preconditioning coil,
  • Dual-path electric system which combines a separate ventilation and return air path in a single unit.
  • Advantages

    The dual path system:

    • Provides direct control of ventilation air quantity, regardless of VAV control on supply air to the conditioned space,
    • Provides excellent humidity control at all times, including part load, as moisture is removed at its source, regardless of building load,
    • Improves indoor air quality and mold and bacteria growth is reduced as there in no standing water in the drain pans. The intensive moisture condensation on the ventilation air coil creates abundant condensate flow, avoiding stagnant standing water.
    • Energy efficient while assuring an acceptable humidity level at all ventilation air volumes. Its use can also reduce demand and energy charges sufficiently to offset the higher first cost.
    • Can be combined with the refrigeration and water heating systems and the heat recovered from refrigeration used in water and space heating.

    Disadvantages

    There is a first cost premium since two coils and compressors are used.

    Applications

    Dual path systems can be installed separately or integrated with additional HVAC or refrigeration equipment. They are currently available in factory packaged units for indoor and outdoor installation. Heat pipe enhancements are available on some models.

    Best applications

    • Where the dual path system can be combined with the refrigeration and water heating systems; heat recovered from refrigeration can be used in water and space heating,
    • HVAC applications requiring good control of outdoor air quantity, and humidity control of supply air,
    • Supermarkets, hospital/health care areas requiring large ventilation air intake.

    Possible applications

    • Schools, commercial and office buildings where indoor air quantity must be increased and old CFC-using or inefficient equipment must be replaced.
    • Process or industrial applications requiring good control of outdoor air quantity, and humidity control of supply air.

    Technology types (resource)

    • Improved single path electric system uses a smaller volume of air is cooled to lower than conventional temperatures (about 40 to 45°F compared to 52 to 56°F), and the remaining air bypasses the cooling coil and is remixed before delivery to the space. This bypass design also permits a smaller compressor since the lower air flow compensates for the larger temperature drop through the coil. Using bypassed air also lowers reheat energy needs, while the smaller ducts and power wiring reduces first cost.
    • Dual-Path electric system uses two cooling coils to separately condition the incoming outdoor and return air. The hot and humid outdoor air and, in some cases, return air is directed to a primary coil for dehumidification, reducing moisture at the source by cooling air to 40 to 45°F. The secondary coil furnishes the sensible cooling of the relatively cool and dry return air as and if needed. These two air streams are then mixed, reducing the reheat energy needs, and supplied to the supermarket.

    Efficiency

    Dual path systems typically will reduce the HVAC installed tons by 15% to 23% over a conventional single path system. Dual path systems typically will reduce the annual energy use (kWh) between 14% and 27%. The reductions will depend on the location and the design parameters.

    Contact us to receive a copy of an EPRI report on Dual-Path Supermarket HVAC Systems or for more information.


    Enthalpy Wheels

    This space-efficient heat transfer method features rotary air-to-air heat exchangers and helps lower relative humidity.

    Heat or enthalpy wheels are rotary air-to-air heat exchangers. Adjacent supply and exhaust air counterflow streams each flow through half of the wheel. Heat wheels have a fill that transfers only sensible heat while an enthalpy wheel's fill transfers total heat.

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    Advantages

    • These wheels are quite compact and can achieve high heat transfer effectiveness,
    • Heat wheels have a relatively low air pressure drop, typically 0.4 to 0.7 in. of water,
    • Freeze protection is not an issue,
    • The cooling or heating equipment size can be reduced in some cases.
    Energy

    Disadvantages

    The use of the heat wheel

    • adds to the first cost and to the fan power to overcome its resistance,
    • requires that the two air streams be adjacent to each other,
    • requires that the air streams must be relatively clean and may require filtration,
    • requires a rotating mechanism that requires it be periodically inspected and maintained, as does the cleaning of the fill medium and any filtering of air streams,
    • in cold climates, there may an increase in service needs,
    • results in some cross-contamination (mixing) of the two air streams, which occurs by carryover and leakage.

    Links to more detail

    Applications

    Heat wheel heat exchanger enhancement can improve system latent capacity. For example, a 1°F dry bulb drop in air entering a cooling coil can increase the latent capacity by about 3%. Both cooling and reheating energy is saved by the heat wheel's transfer of heat directly from the entering air to the low-temperature air leaving the cooling coil. It can also be used to precool or preheat incoming outdoor air with exhaust air from the conditioned spaces.

    Best applications

    • Where lower relative humidity is an advantage for comfort or process reasons, the use of an enthalpy wheel pipe can help. An enthalpy wheel used between the warm air entering the cooling coil and the cool air leaving the coil transfers sensible heat to the cold exiting air, thereby reducing or even eliminating the reheat needs. Also the enthalpy wheel heat precools the air before it reaches the cooling coil, increasing the latent capacity and possibly lowering the system cooling energy use.
    • Projects that require a large percentage of outdoor and has the exhaust air duct in close proximity to the intake, can increase system efficiency by using a heat wheel to transfer heat in the exhaust to either precool or preheat the incoming air.

    Possible applications

    • Existing buildings where codes require it or they have "sick building" syndrome and the amount of outdoor air intake must be increased,
    • New buildings where the required amount of ventilation air causes excess loads or where the desired equipment does not have sufficient latent capacity.

    Technology types (resource)

    A small motor and belt drive rotates the wheel and its fill medium. Sensible heat is transferred as the hot air stream passes through the fill which picks up and stores heat and then releases it as the fill rotates into the cold air stream.

    Latent heat is transferred as the wheel fill

    1. condenses moisture from the air stream with the higher humidity (either due to a fill temperature below the air dewpoint or because the fill includes a desiccant) and heat is released, and
    2. releases the moisture through evaporation ( and picks up heat) as the fill rotates into the air stream with the lower humidity ratio. Both latent and sensible heat is transferred simultaneously as the moist air is dried and the dry air is humidified.

    Fill for the heat wheel is typically made of aluminum for HVAC applications. Fill for total heat recovery is made from a number of different materials and treated with a hygroscopic material such as lithium chloride, alumina, or aluminum oxide, each of which has specific moisture pickup properties.

    Seals divide the fill from the two air streams, but there is some carry-over as the air entrained within the fill is carried into the other air stream. Leakage occurs due to the static air pressure difference between streams which drives some air from the higher pressure stream into the lower pressure one. Cross-contamination problems can be reduced by placing the fans so they promote leakage of the ventilation air into the exhaust air stream.

    Carry-over can be further reduced by adding a purge section to the wheel where some supply air is bypassed through a section of the fill before the main supply passes through the wheel. This is typically done in critical applications such as hospital operating rooms, clean rooms, and labs.

    Wheel heat recovery is controlled using two methods. One is to bypass supply air around the wheel and mixed with the remaining air to regulate temperature. The other is to control the rotating speed of the wheel with a variable speed drive.

    Efficiency

    Heat wheels typically have a sensible effectiveness of 50% to 80% and a total effectiveness of 55% to 85%.

    Other information

    Visit here for a detailed list of manufacturers for this equipment.


    100% Outside Air Units

    These factory packaged units are most suited where a large amount of ventilation air intake is required.

    Applications requiring 100% outside air intake for ventilation, odor removal or other reasons can benefit from the use of factory packaged all-outdoor air units. They can be as simple as only a fan-filter unit, heating only, heating and evaporative cooling, heating and chilled water or direct expansion mechanical cooling, desiccant systems, and those incorporating heat recovery enhancements.

    Advantages

    • Factory engineered and matched components can be custom-designed to handle all outdoor air loads (sensible and latent) and its filtering requirements,
    • Condensate drains within terminal units are kept dry, cleaner and easier to maintain,
    • Chiller and air handler unit sizes can be reduced on new installations as they need only handle the sensible load; these savings can offset the cost of the separate outdoor air system,
    • Terminal equipment control is simplified as requires only a dry bulb thermostat,
    • Amount of ventilation air can be controlled, thus avoiding "sick building" syndrome without excessive operation costs.

    Disadvantages

    Added cost of separate ventilation air system may not be justified in all cases.

    Applications

    Changes in building construction and use has caused lower sensible cooling loads due to increased insulation, better windows, and more efficient lighting. At the same time, higher ventilation air requirements, together with higher building occupant densities, result in higher dehumidification loads which means higher moisture (latent) loads.

    At the same time the demand for higher efficiency cooling units has manufacturers using larger evaporators operating at higher refrigerant temperatures, resulting in reduced moisture removal ability compared to the sensible capacity...a higher sensible heat ratio of the equipment.

    Conventional systems use refrigeration to provide both sensible (lower the air temperature) and latent (dehumidify the air) cooling. To achieve the lower relative humidity desired in some spaces, the air must be cooled below that needed for the sensible load in order to remove sufficient moisture, and then reheated to prevent over-cooling thus increasing energy use. Separating the sensible load, handled by conventional means, and the latent load, handled by a 100% outside air unit providing the required amount, fully filtered and dehumidified of ventilation air is becoming a more practical way of handling today's requirements.

    Best applications

    Applications requiring a large amount of ventilation air intake offer the most advantages for the use of 100% outdoor air units.

    Where the sensible heat ratio is lower (high latent load) than can be maintained by conventional systems, a separate outdoor air system provides many advantages, both in new systems and the retrofit of existing systems.

    They can be used to retrofit a project where the installed conventional equipment can not maintain the desired humidity levels or where conditions have changed to create a humidity problem (example: original design had too low an outdoor air intake). Heat recovery options are often coupled with pre-conditioned outdoor air systems to improve performance.

    Possible applications

    With a VAV system, outdoor air is a percentage of supply air, which can be below minimum requirements during the partial load conditions that occur during most of the year. Retrofits of a VAV system can be one alternative where poor air quality is experienced.

    Technology types (resource)

    The unit components are enclosed in a modular factory-fabricated casing, usually designed for outdoor installation, mounted on a structural frame that can withstand the rigors of shipment and rigging into place in the building. The selected components are custom designed to meet the specific needs of the project. Typically they include air intake louvers and filters, air supply fan with motor and drive, heating and cooling coils, and supply air duct connection.

    These units can include optional dehumidification and heat recovery exchangers with several types available (heat pipe, heat wheel, air-to-air), optional bypass dampers and controls, and desiccant wheel options. Other options are wide and varied, and may include winter humidification, optional air foil fans, indirect evaporative cooling coil, high efficiency filters, roof mounting curbs, horizontal or vertical supply air connections, integral exhaust air fan with motor and drive, separate exhaust-to-supply air heat exchanger, and various control options including supply air temperature and humidity control, outdoor air sensor for summer/winter changeover, and building pressurization control. Motors and controls are factory wired to a central control cabinet and include fusing, motor starters, and disconnect switches. Other options include direct and indirect gas-fired heating, and separate matching air-cooled condensing unit.

    Efficiency

    The efficiency of these units is largely dependent on the extent of heat recovery or dehumidification options that are included in the selected design.

    Contact us for a detailed list of manufacturers for this equipment.

    Other information




    Security Lighting

    Improve your facility's safety and security with adequate lighting.

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    Commercial facilities install safety and security lighting so that employees and/or customers feel safe when entering or leaving the facility during darkness. They also install security lighting to prevent break-ins and theft.

    The lighting design should give adequate lighting for safety in the parking lot. It should also provide lighting along routes from the building to the parking lot. For example, the main entrance and sidewalk may need illumination.

    Security lighting should be such that security personnel or police can see a theft in progress. Merely having security lighting can deter a thief because they feel vulnerable in the light. The lights should be placed at strategic locations such as rear or hidden entrances where a thief might exit. Very often, security lighting must provide adequate illumination for surveillance equipment. However, it's important that safety and security lighting not create glare for those in the area.

    Sometimes aesthetics is important, especially if the lighting is installed at the main entrance. If so, metal halide will be the best choice of light sources. Otherwise, high pressure sodium, and even low pressure sodium lamps are adequate. Low pressure sodium doesn't provide any color rendition at all, but is a good choice for security lighting because it's very efficient. Fixtures placed at main entrances and entry sidewalks usually need to be attractive. Bollards are popular for sidewalks as are post top fixtures. If the main entrance or sidewalk is covered, then surface-mounted fixtures or recessed-can fixtures are a good choice.

    When aesthetics aren't as important, wall pack fixtures are usually adequate for safety and security purposes. However, if the area is large, then directional flood fixtures will light the area more efficiently. Be sure to aim directional flood fixtures properly, especially when mounted on t he building, because glare and light trespass can be a problem. Open Bottom, Type-five fixtures are also a good choice for larger areas. They can be mounted on the building or on a pole.


    Façade Lighting

    Make a grand first impression with dramatic lighting touches.

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    Lighting the façade of a commercial building or home adds beauty and makes the structure stand out. Of course, color rendition is usually a priority. However, fixture aesthetics is typically not a concern since the fixtures are often hidden from view.

    It's common to mount fixtures on the ground, on poles or sometimes on the building or a nearby structure. Head-on flood lighting will make the structure appear flat and uninteresting. It's better to place fixtures at an angle to help bring out textures and structural features. By aiming fixtures up the facade instead of down will avoid creating glare. Placing the fixtures close to the building will reduce glare for viewers inside the building. This is especially important for hotels and penthouse restaurants.

    Adjustable flood-type fixtures are best for facades. Choose a fixture with a beam spread that will light the target without spill light. Fixtures mounted on the ground may need metal guards or other protection from vandalism.

    Halogen or quartz lamps are a good choice for smaller areas. However, maintenance and operating costs will be high. A better choice of lamp that still provides good color rendition is metal halide. High pressure sodium looks good as well, especially on historic buildings. Mercury vapor is appropriate for lighting copper roofs to bring out the green patina. The HID lamps offer much longer life and lower operating costs than the halogen and quartz lamps.

    Time clock control may be more desirable than photocell control, since it can be set to turn off the façade lighting during the later portion of the night when there are few passers-by.


    Landscape Lighting

    Enhance your landscape investment with special lighting effects.

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    Landscape lighting can beautify the surroundings of a building or complex. Much like an artist paints a landscape, a landscape lighting designer chooses elements in the landscape to emphasize. Ideally the designer has a thorough knowledge of plants and works with the landscape designer to plan the lighting scheme and placement.

    Contrast is important because it directs where and how the viewer sees the landscape features. Primary focal points appear brightest. Secondary focal points and the background are lit at lower levels. By using fill lighting between the focal points you provide cohesion.

    The light levels required will depend on the surrounding community. Downtown areas require higher levels than suburban or rural areas. It's also desirable to reduce glare by properly aiming and locating fixtures. Illuminate steps, stairs and walkways to clearly identify their boundaries and changes in elevation. Uniformity of illumination is also important in these areas.

    Flexibility is important when trying to light plants. Since they grow and change, the fixtures need to be able to change aiming, location, beam spread or wattage. Illuminate dense plants, with foliage close to the ground, by placing fixtures away and aiming toward the plant. Other plants with more open form or translucent leaves can be lit from within. Trees should be lit such that their overall shape is visible. Illuminate the trunk to tie it to the ground. The light source to use depends on the element to be lit, the size of the project and the desired effect. High pressure sodium is good for red or yellow blossoms and autumn foliage. Metal halide and mercury vapor are good for most greens and blue green foliage. Metal halide and incandescent are good for tree bark.

    Fixtures shouldn't detract from the daytime landscape. So locating the fixtures behind plants or structures, or up in trees is especially important. The fixtures must also be able to withstand the weather. Like Faade lighting, vandalism can be a concern. For flexibility, control the fixtures with either a timeclock or switches. Landscape lighting probably doesn't need to operate all night. Small landscapes can use smaller wattage lamps.


    Parking Lot Lighting

    Soothe customer and worker anxiety with well-lit parking areas.

    IES recommends illuminance levels for parking lots are similar to roadway illuminance levels based on the amount of nighttime activity expected, both pedestrian and vehicular. Nighttime activity classifications are high, medium or low.

    • High activity areas include: sport arenas, major civic or cultural events, regional shopping centers and fast food facilities.
    • Medium activity areas include: community shopping centers, office parks, hospital parking areas, transportation parking such as airports, cultural, civic or recreational events, residential complex parking.
    • Low activity areas include: neighborhood shopping, industrial employee parking, educational facility parking, church parking.

    If the nighttime activity involves large numbers of vehicles, then the activity level for low or medium should probably be bumped to the next higher level. Based on the activity level, decide the average maintained illumination level. 2 fc for High - 1 fc Medium - And Low - 0.5 fc.

    Where pedestrian traffic is present, as in most parking lots, IES also specifies the minimum illumination levels required: 0.9 fc for high, - 0.6 fc for medium and 0.2 fc for low. For example, an apartment building parking lot falls into the medium activity level. So the recommended average fc level is 1 and the minimum is 0.6 fc.


    Lighting Maintenance Programs

    Reap substantial savings through well-planned light-changing and fixture maintenance programs.

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    In many cases, light changing maintenance programs and procedures can result in substantial savings. Simple techniques such as regularly cleaning fixtures, lamps and lenses; following relamping schedules; cleaning surfaces in the space; and other techniques improve the quantity and quality of light created by the existing system and can produce both cost and energy savings. Dust, grease, and other dirt accumulations on lamps, lenses, globes, and reflecting surfaces of the fixture can reduce light output by as much as 30 percent. Lighting professionals recommend that fixtures be cleaned every two or three years. In greasy, dusty, or smoky settings, or when light fixtures are integrated with the HVAC system, cleaning may need to be more frequent.

    Check to see how clean the lamps and fixtures are, and do any necessary cleaning before deciding on efficiency changes in the lighting. Cleaning will increase the light output and may allow you to remove some lamps or to install lower wattage ones. To maintain your lighting efficiency gains, cleaning is particularly important. If you have reduced light levels in previously overlighted areas, timely cleaning will assure you of continuing to have enough light for the needs of each area.

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    As fluorescent lamps age, their light output decreases, yet they consume the same amount of energy producing this lower light level. Timely replacement of old lamps eliminates this inefficiency. A practice that is becoming common in facilities with a large number of ceiling lights is group relamping, or replacing all lamps in an area near the end of their useful life. Group relamping can cut replacement labor costs in half when efficiently done by a team going from fixture to fixture, and it can assure proper light levels, because fluorescents dim as they age. It also helps prevent unwanted interruptions in work or some other activity when individual lamps burn out at random.



    Ozone is a strong oxidizer and can be particularly effective for aqueous waste streams with less than 1% organic content. It is sometimes used as a pretreatment method or to disinfect wastewater after biological treatment.

    Ozone oxidizes a wide range of organics, can destroy cyanide wastes and phenolic compounds, and is faster acting than alkaline chlorination. And, unlike chlorine, ozone doesn't generate toxic ions in the oxidation process.

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    Ozone is the triatomic form of oxygen formed naturally during lightning strikes and anytime an electric arc is formed. It is a very unstable compound and must be produced at the same time it is needed, usually by ultraviolet excitation and corona discharge. It isn't effective in treating slurries, sludges, solids, organic solvents, or tars.

    Before use, consider the possibility that ozone will oxidize other stream components that didn't need treatment. Excess ozone (that is, ozone not consumed in the reaction) must be catalytically decomposed since release isn't permitted.

    Manufacturers
    Aqua-Flo, Inc.
    6244 Frankford Ave.
    Baltimore, MD 21206
    (410) 485-7600
    EDC Ozone Systems
    3110 W. Story Rd.
    Irving, TX 75038
    (972) 257-0322
    GuestCare, Inc.
    3030 LBJ Freeway, Ste. 1460
    Dallas, TX 75234
    (972) 243-3035
    Prozone International, Inc.
    3122 12th Ave. SW
    Huntsville, Al 35805
    (205) 881-4570
    Pure Water
    3725 Touzalin Ave.
    Lincoln, NE 68507
    (402) 467-9393
    Oxygen Technologies, Inc.
    8229 Melrose Dr.
    Shawnee Mission, KS 66214
    (913) 894-2828

    Put a chill on high cooling bills with recent advances in space cooling technology

    For most facilities, cooling interior spaces is one of the larger energy expenses. Fortunately, modern alternatives to traditional space cooling systems offer greatly improved efficiency and performance over older equipment.

    Click on a topic of interest below for more information about specific space cooling technologies.



    Heat Pumps

    Gain energy savings by removing heat from areas where it's not needed and moving it to areas where it is needed.

    A heat pump is a device that extracts heat from a source and transfers it at a higher temperature. While all mechanical cooling systems are technically heat pumps, in HVAC terms, "heat pump" is reserved for equipment that can heat for beneficial purposes, rather than equipment that only removes heat for cooling. Dual mode heat pumps can provide either heating or cooling, while heat-reclaim heat pumps provide heating.

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    An applied heat pump requires competent engineering for the specific application as opposed to the use of a manufacturer-designed unitary heat pump. The distinction between some models and applications can be rather fuzzy.

    Heat pumps provide an important amplification of temperature that simple heat exchangers can not do. For example, efficient heat exchangers can preheat water or air up to 2 to 5°F of the temperature of the heat source - but never as hot or hotter than the waste heat source. If a higher temperature is required, then a heat pump or a combination of heat exchanger and heat pump must be used.

    Most heat pumps used in HVAC applications today use a vapor compression cycle, similar to that used in a household refrigerator or home air conditioner and use an electric motor driven compressor, a condenser and an evaporator. Dual mode heat pumps include some form of cycle reversal where heating and cooling effects can be switched. Compressors can vary from small hermetically sealed units to large centrifugal machines. Industrial processes can be served by either this closed-vapor compression cycle, or by an open or mechanical vapor recompression or MVR cycle.

    Typical waste heat sources include outdoor or exhaust air, condenser or cooling tower water, well or other ground or surface water and heat rejected from industrial processes. The selection of the source depends on several variables such as suitability, availability, cost, and temperature. Where the source availability and the useful heat needs are not coincidental, thermal storage on either the hot or cold side should be considered.

    Advantages

    Heat pumps provide an important amplification of temperature that simple heat exchangers can not do.


    Unitary Heat Pumps

    Get year-round space cooling at a competitive cost with individual room or zone control.

    Unitary heat pumps are factory-packaged refrigerant-based heat pumps that are available in a number of application categories which include:

  • Packaged terminal heat pumps (PTHP)
  • Closed water loop heat pump systems
  • Ground-Coupled (Closed-Loop) Systems
  • Ground water-source heat pumps
  • Large unitary air- and water-source heat pumps
  • In each category there are several possible configurations, including:

    • Single package, with all components in a single enclosure
    • Roof-top packages - a variation on the single package
    • Split units, with remote outdoor coil, fan, and/or compressor
    • Air and water-source heat pumps
    • Heating only heat pumps

    Package units and the indoor sections of split units are available in several configurations:

    • Vertical for closet installations,
    • Console for installation under windows, and
    • Horizontal for ceiling or outdoor locations.

    Some models have decorative casings. Others can be built-in. With the exception of large unitary heat pumps, the units are designed for free-air delivery or with short duct connections between the unit and the conditioned space. Most heat pump manufacturers participate in the Air-Conditioning and Refrigeration Institute (ARI) Certification Program. Product performance (below 135,000 BTUH sizes) is listed in the ARI Directory of Certified Products. This allows a performance comparison of various models from various manufacturers. Sizes range from l/2-ton package terminal heat pumps up to rooftop units of 30-tons or more. Many are provided with supplemental electric heaters to satisfy the load when the outdoor temperatures drop below the set point. Gas fired supplemental heat is also available in a limited range of equipment. Most heat pumps are sold and installed by local air conditioning contractors, who also provide routine service and repair. Depending on the nature of the application, this availability of fast service can be very important in equipment selection.

    Advantages

    Unitary heat pumps

    • They provide individual temperature control in small occupied zones during nights and weekends without the need for a large central plant chiller or boiler and their associated pumps,
    • The heat pump's consumption of electricity can be separately metered.

    Water loop heat pumps

    • They don't require wall openings to reject heat from air-cooled condensers,
    • They aren't exposed to the weather and therefore tend to have a longer service life,
    • If a unit fails, the entire system doesn't shut down, however, failure of a loop pump, heat rejection device or secondary heater can affect the entire system.

    Disadvantages

    • Imprecise temperature and humidity control,
    • In-room or in-space maintenance including frequent filter replacement,
    • Water loop systems require regular loop maintenance, and
    • These systems require space for pumps heat exchangers and boilers (if a boiler is required).

    Applications

    Unitary heat pumps can provide year-round electric air conditioning at a competitive cost with the feature of individual room or zone control. They can be used in almost any type room or building. They can be used in a variety of engineered system arrangements (i.e. closed water loop, etc.) to provide economic operating costs and desired features (night setback, etc.) not available in other systems.

    Best applications

    They are best applied:

    • Where there aren't competitive alternative heating energy sources,
    • In climatic areas with moderate heating loads, and
    • Where individual room or zone control is required for customer satisfaction. They offer the most advantages when combined in any of the many available engineered system arrangements.

    Possible applications

    Unitary heat pumps can be applied in almost any building as they are extremely versatile. The basic customer decision is whether the requirements of a particular application can be best served by unitary system or by a central chilled water system. The required features, floor space and weight, ceiling height, cost factors, maintenance factors, operational factors all need to be considered and evaluated.

    Technology types (resource)

    Unitary air and water source heat pumps are available as larger capacity commercial self-contained units which serve large zones using ducts for air distribution. Air source units must be located along outside walls or on the roof. They tend to have higher operating costs than central plants or water-source heat pumps.

    • Water-source units can be located anywhere but require ventilation air ducts. They are usually connected to a cooling tower circuit for heat rejection when they are in the cooling mode, and to a central hot-water heater or strip heater when heating is required. Advantages include low first cost and the availability of optional accessories (variable air volume control, economizer cycle, night setback and morning warm-up).
    • Large system heat pump applications are often applied in, buildings using two- or four-pipe water distribution systems, or in industrial applications. Many large buildings require cooling the year-round due to large internal loads from lighting, electronic and other business equipment. Only the perimeter zones of these structures ever need heating. The warm condenser water from the water chillers serving this cooling load can be used as a heat source. The water-to-water heat pump is piped in a cascade system, using this waste heat to preheat domestic hot water or provide hot water to satisfy building space or reheat loads. Units are available to heat water from 105°F to 120°F, or even higher if needed. The lower the hot water temperature required, the lower the energy consumption.
    • In some cases, the units are combined into a single heat recovery chiller with a double-bundle condenser. The house water condenser serves the hot water loop for the building. When the waste heat exceeds the heat requirement, the excess heat is rejected in the second tower water condenser. Thermal storage can also be integrated into this system. Other options include integration with closed loop water-to-air heat pumps, or secondary heat recovery from water loop heat pump systems.
    • Air-to-water heat pumps perform in a similar manner but typically use warm exhaust air as the heat source. They are often referred to as heat pump water heaters and are used in hotels, restaurants, laundries and other applications needing a lot of hot water.
    • Many industrial processes have low-level waste heat that must be rejected. Factory-packaged, closed-cycle refrigerant-based heat pumps are available to heat water to 120°F or warmer. Using waste heat for this purpose off-loads cooling towers or evaporative condensers while reducing boiler fuel consumption and the corresponding products of combustion.

    Efficiency

    Most heat pump manufacturers rate their equipment in accordance with ARI standards and participate in the ARI certification programs. ARI Standard 210/240 covers air-source units, ARI Standard 330 covers ground source closed loop heat pumps, ARI Standard 325 covers ground water-source heat pumps, ARI Standard 310/380 covers packaged terminal heat pump air-source units, and ARI Standard 320 covers water-source heat pumps.

    Packaged terminal heat pumps typically have cooling energy efficiency ratios (EER) in the range of 9.0 to 11.0 Btu per watt of electrical energy input and a heating coefficient of performance (COP) in the range of 2.7 to 3.3 .

    Air-source heat pumps typically have cooling seasonal energy efficiency ratios (SEER) in the range of 10.0 to 14.0 Btu per watt of electrical energy input and a heating seasonal performance factor (HSPF) in the range of 6.0 to 9.0 Btu per watt of electrical energy input.

    Water-source heat pumps typically have cooling energy efficiency ratios (EER) in the range of 10.0 to 15.0 Btu per watt of electrical energy input and a heating coefficient of performance (COP) in the range of 3.7 to 5.2.

    Refer to the segment on ground coupled and ground source heat pumps for a discussion on the efficiency of these heat pumps.


    Ground Water Source (Open Loop) Heat Pump Systems

    Save energy by using surface or underground water (lake, river, well, etc.) as a cooling and heating source.

    An open-loop, ground-water heat pump, uses a surface or underground water source (such as a lake, river, or well) as the heat source and sink. Well water designs are the most common and seem to be the most cost effective. The well supplies both domestic water and water for the heat pump. Approximately three gallons per minute of well water are needed per ton of cooling capacity.

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    Ground water source open-loop heat pumps use the same concept as the ground coupled units - for example, in the Midwest the temperature of the earth near the surface and the water in it (aquifer) is typically around 55°F. Water is taken from the ground or surface water (pond, lake, etc.), circulated to the individual heat pumps and the returned to the ground via a disposal well, returned to the lake or pond, or where permitted discharged into a stream or river.

    When more units are heating than cooling the circulating water temperature drops prior to disposal. Conversely, when more units are cooling than heating, the circulating water is warmed prior to disposal.

    Advantages

    In both commercial and residential installations, geothermal heat pump systems typically have lower maintenance costs than conventional systems as all equipment is installed inside the building or underground. This means that there is no outside equipment exposed to weather and vandalism. All refrigerant systems are sealed, similar to household refrigerators.

    • Open loop systems have less loss in heat transfer
    • Open loop systems have lower heat pump energy costs
    Geothermal systems are very flexible. They can be easily and inexpensively subdivided or expanded to fit building remodeling or additions. They are particularly well-suited to "tenant finish" installations.

    In commercial installations, systems can save money by recovering excess heat from building interior zones and moving it to the perimeter of the building. They can also save money by allowing management to isolate and shut down unoccupied areas of the building.

    Disadvantages

    • Problems associated with disposal of the water after once-through the heat pump, disposal wells can be costly,
    • Water which has suitable qualities could change with time to poor quality that causes problems of corrosion later in time,
    • Costs associated with the drilling of the water well can be high and unknown at the outset,
    • Water tables and well output can change over time and cause future problems,
    • Permitting and its costs are usually required,
    • Open-loop systems have more potential problems than either conventional systems or closed-loop geothermal systems because they bring outside water into the unit. This can lead to clogging, mineral deposits, and corrosion in the system.
    • Open-loop systems require a large supply of clean water in order to be cost effective. This often limits their use to coastal areas, and areas adjacent to lakes, rivers, streams, etc. In addition, there must be an acceptable method of returning the used water to the environment. This may be limited not only by environmental factors (such as no place to dump that much water), but also by local and state regulations.
    • Since accessibility to terminal units is important in geothermal systems, architects and mechanical and structural designers must carefully coordinate their work.
    • Each unit requires both electrical and plumbing service.
    • Duct systems must be installed to bring outside air to each space.
    • Secondary or backup heat sources are required in cooler climates.

    Applications

    Open loop heat pumps can be applies wherever there is an ample source of good quality water is available along with an adequate and permitted disposal method.

    Best applications

    Best Applications Where water supply and quality is known and water use is not now, or expected to be, regulated; and where a closed loop system may not be applicable.

    Technology types (resource)

    Manufacturers of products certified by the Air-conditioning and Refrigeration Institute (ARI) Standard 325 for ground water-source heat pump equipment publish a capacity rating for each model catalogued at the standard entering water rating conditions of both 70 and 50°F for cooling and heating. The cooling EER, heating COP and water flow for both is also published. In calculating the cooling Standard Energy Efficiency Rating (EER) and the heating Coefficient of Performance (COP), a water pump penalty effect is added to the measured power input.

    You should not confuse the ARI Standard Energy Efficiency Rating with the expression SEER. The latter stands for Seasonal Energy Efficiency Ratio. SEER is a measure of seasonal cooling efficiency under a range of weather conditions, assumed to be typical for a location, and of performance losses due to cycling under part load conditions.

    Most manufacturers publish performance ratings on their various models. These ratings are usually specified by a model number at a fixed air flow in cubic feet per minute (cfm) with the following variables:

    • Several fluid flow rates in gallons per minute,
    • Entering water temperatures from 35 to 100°F,
    • Entering air temperatures at 80°F dry bulb and 67°F wet bulb for cooling, and
    • Entering air at 70°F dry bulb for heating.

    The following rating values are given for cooling for each of the above variables:

    • Total capacity in Btu per hour,
    • Sensible capacity in Btu per hour,
    • Heat rejection to the water in Btu per hour,
    • Power input in watts, and
    • Energy efficiency rating (EER), which is the total capacity divided by the power input, or Btu per watt.

    Also, for each of these variables, the following rating values are given for heating:

    • Total capacity in Btu per hour,
    • Heat absorption from the water in Btu per hour,
    • Power input in watts,
    • Coefficient of Performance (COP), which is the total capacity divided by the power input converted to Btu per hour, and multiplied by 3.412 Btu per hour per watt.
    It is important not to extrapolate from the data tables provided by manufacturers. Extrapolation removes the data from the context and boundaries of the table, and is not a good engineering practice. This is why most manufacturers say that interpolation between ratings within a table is permissible, but extrapolation is not.

    Other published data typically includes:

    • Correction factors given for various other entering air conditions, dry and wet bulb, and other air flow ratings,
    • The unit water pressure drop is also published for each flow rate, in either feet of water or pounds per square inch (psi),
    • Blower performance including fan motor brake horsepower (bhp), and external static pressure capability,
    • Electrical data on voltages and current draw,
    • Physical data including operating weight and refrigerant charge, and Hot water generating capacity.

    Efficiency

    In general, efficiency is defined as the Useful Work or Energy Delivered divided by the energy supplied to do that work. In heating and cooling with heat pumps, the definition is changed somewhat. For cooling the efficiency is expressed as the Energy Efficiency Ratio - EER.

    If the unit cooling capacity and EER is known, the kW power input can be calculated. For example, a unit having a total cooling capacity of 26,000 BTUH at an EER of 11.4, the cooling unit power input is:

    26,000 BTUH / 11.4 x 1000 watts/kW = 2.28 kW

    For heating, the efficiency is expressed as the Coefficient of Performance or COP. If the unit heating capacity and COP is known, the kW power input can be calculated. For example, a unit having a heating capacity of 33,500 BTUH at a COP of 3.9, the heating unit power input is:
    33,500 BTUH / 3.9 COP x 3,413 BTUH/kW = 2.51 kW

    Keep in mind the unit EER and COP are dependent on the entering ground water temperature, water flow rate through the unit, airflow rate and the entering air temperature. High efficiency equipment comes with a higher price tag. It is difficult to state a general rule about selecting equipment on the basis of efficiency because of the economic considerations and the merits of each system and the equipment used with it.

    Air flow is typically selected to be between 300 and 525 cfm per ton of cooling capacity. 400 cfm per ton is typical. The final selection will be governed by the sensible to total load ratio.

    Water flow through each unit should be designed to simplify water balancing. To do this, the system should be designed to keep unit water pressure drops as close as possible to each other. Though the target water temperature rise is usually 12°F. or 2.0 gpm per ton, they can range from 8 to 15°F, equal to 3 to 1.6 gpm per nominal ton of cooling capacity.

    The gpm per ton can be derived from the following formula: 12,000 divided by the result of the temperature rise, times 500. In this formula, 500 equals water at 8.33 pounds per gallon times 60 minutes per hour.

    Contact us for a detailed list of manufacturers for this equipment.


    Ground Source (Refrigerant Loop) Heat Pump Systems

    Lower utility bills with this refrigerant-based system that uses the ground's constant near-surface temperature of 55¼ as a heating and cooling source.

    Ground source closed-refrigerant-loop heat pumps use the same concept as the ground coupled units. For example, in the Midwest the temperature of the earth near the surface is typically around 55°F. With ground coupled systems water is taken from the ground or surface water (pond, lake, etc.), circulated to the individual heat pumps and the returned to the ground. With refrigerant loop systems a refrigerant such as R-22 is substituted for the water.

    The Refrigerant Loop or Direct Expansion system circulates refrigerant, instead of water or antifreeze. The refrigerant is circulated in copper piping buried in the ground, rather than plastic piping. These systems are potentially more efficient than water loop systems.

    Advantages

    • Fewer feet per ton of buried piping are needed since copper is a better conductor of heat than plastic.
    • No freeze protection problem since no water or antifreeze is required.
    • Heat is transferred directly from the refrigerant to the earth. There is no loss of efficiency due to the lower refrigerant temperature needed to first transfer heat into the water and then into the ground.
    • Many contractors have well-developed skills with copper pipe.
    • No fusion techniques are required.
    • No purge and flush operations are required.
    • No circulating pumps are needed, and
    • The system has lower operating costs.

    Disadvantages

    • Refrigerant management and oil return is important. The length of the copper piping is limited in order to achieve oil return and to minimize the refrigerant pressure drop losses. This precludes its application to many commercial buildings.
    • Environmental issues related to the system's use of more refrigerant than the water loop systems.
    • Corrosion issues, since the copper piping needs anodic protection and can be harmed by acidic soil conditions which can develop over time.
    • Operating with too low a refrigerant temperature in winter can freeze the ground and reduce heat transfer.
    • Operating with too high a refrigerant temperature in summer can bake the ground and reduce heat transfer.
    • Industry acceptance with comparatively few products available, no ARI standard, and few experienced contractors.

    These systems are in the field development stage and will not be addressed any further.

    Contact us for a detailed list of manufacturers for this equipment.


    Ground-Coupled (Closed-Loop) Heat Pump Systems

    Reduce utility bills with this system that cycles water through the ground's constant near-surface temperature of 55¼ to aid in heating and cooling.

    Ground source closed-loop heat pumps use the same concept as the ground source open-loop units - the temperature of the earth near the surface is typically around 55 ° F. The difference is no water is taken from the ground or disposed of. The water is circulated to the individual heat pumps and the returned to a ground closed-loop to be cooled or warmed.

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    When more units are heating than cooling the circulating water temperature drops and is warmed back up by the earth in the ground heat exchanger. Conversely, when more units are cooling than heating, the circulating water is cooled down by the ground heat exchanger buried in the earth.

    The closed-loop ground-coupled system uses a buried or submerged geothermal heat exchanger. This heat exchanger can reject or draw heat from a source such as the earth, a lake, or a pond, by circulating water through a closed-loop. This heat exchange loop may be pipe coils installed horizontally, vertically (down-hole), in a coil, or in other configurations. The down-hole system is used when surface area is limited since horizontal or even spiral coils can take up a lot of room and run up excavation costs.

    Advantages:

    • Geothermal heat pump systems have lower operating costs, lower maintenance costs, lower life cycle costs, increased reliability, and greater comfort than alternative cooling and heating systems.
    • There is no outside equipment exposed to weather and vandalism, and no exposed equipment where children can get hurt.
    • In both commercial and residential installations, geothermal heat pump systems typically have lower maintenance costs than conventional systems as all equipment is installed inside the building or underground. All refrigerant systems are sealed, similar to household refrigerators.
    • Geothermal systems are very flexible. They can be easily and inexpensively subdivided or expanded to fit building remodeling or additions. They are particularly well-suited to "tenant finish" installations.
    • In commercial installations, systems can save money by recovering excess heat from building interior zones and moving it to the perimeter of the building. They can also save money by allowing management to isolate and shut down unoccupied areas of the building.
    • Since units can be installed in a portion of an equipment room or small closet, it gives owners more usable space.
    • In retrofit situations, they can replace rooftop equipment or a central chiller and boiler.
    • Industry standards, set by the Air-Conditioning and Refrigeration Institute, provide consumers with easy to find and consistent support in choosing equipment. They establish standards for testing and rating products, and certify the performance ratings that participants publish.
      Geothermal heat pump systems have lower operating costs, lower maintenance costs, lower life cycle costs, increased reliability, and greater comfort than alternative cooling and heating systems.
    • There is no outside equipment exposed to weather and vandalism, and no exposed equipment where children can get hurt.
    • In both commercial and residential installations, geothermal heat pump systems typically have lower maintenance costs than conventional systems as all equipment is installed inside the building or underground. All refrigerant systems are sealed, similar to household refrigerators.
    • Geothermal systems are very flexible. They can be easily and inexpensively subdivided or expanded to fit building remodeling or additions. They are particularly well-suited to "tenant finish" installations.
    • In commercial installations, systems can save money by recovering excess heat from building interior zones and moving it to the perimeter of the building. They can also save money by allowing management to isolate and shut down unoccupied areas of the building.
    • Since units can be installed in a portion of an equipment room or small closet, it gives owners more usable space.
    • In retrofit situations, they can replace rooftop equipment or a central chiller and boiler.
    • Industry standards, set by the Air-Conditioning and Refrigeration Institute, provide consumers with easy to find and consistent support in choosing equipment. They establish standards for testing and rating products, and certify the performance ratings that participants publish.

    Disadvantages

    • Geothermal heat pump systems may require a higher initial investment to cover the incremental cost of the ground loop.
    • Space is required for installing the ground loop,
    • They require a knowledgeable contractors to assure correct installation, check-out, start-up and operation.
    • Since accessibility to terminal units is important in geothermal systems, architects and mechanical and structural designers must carefully coordinate their work.
    • Each unit requires both electrical and plumbing service.
    • Duct systems must be installed to bring outside air to each space.
    • Secondary or backup heat sources, and use of a loop anti-freeze solution, are required in cooler climates.

    Applications

    Closed-loop heat pumps can be applied wherever there is space to install the horizontal, vertical or other configuration ground loop. Current installations range from small residences to schools and large commercial or institutional buildings.

    Commercial Application Benefits In addition to the general benefits of a geothermal system, there are other advantages for the commercial user to install a geothermal heat pump system.

    Efficiency

    In the heating mode the geothermal heat pump system extracts two-thirds or more of its energy from the earth and moves it to the heat pump unit. Only one-third of the energy needed is purchased power. This is used to run the compressor, circulating pumps and fan.

    In the cooling mode, the unwanted heat is transferred back into the earth for reuse in heating.

    No ground level outdoor equipment

    All of the equipment needed can be installed in one or more mechanical equipment rooms, above dropped ceilings, or on the roof. Except where roof-top units are installed, there are no visible outdoor units to suffer from deterioration due to weather or vandalism, and no outdoor noise. The rest of the equipment consists of an array of piping buried beneath the ground. These pipes can be installed in a vertical well system, horizontally buried under the surface, or installed in a pond. In some cases, well or pond water can be used directly without buried pipe.

    Environmental

    Geothermal heat pump systems produce no on-site pollutants, improve indoor air quality, and reduce the amount of pollutants at the generating station when compared to other forms of electric heat. They also result in lower carbon dioxide emissions which reduces the threat of global warming.

    Service hot water

    In cooling mode, the unwanted heat can be used to preheat hot water at a very low operating cost. In winter, surplus heat can be used in the same way.

    Warmer air distributed during heating

    No more seemingly cold drafts from the air outlets often encountered with conventional heat pumps.

    No supplemental heat

    Most geothermal systems can operate year-round without supplemental direct heat.

    Little or no out-of-pocket incremental cost

    Any added initial cost can often be included in the project financing, and the operating cost savings used to amortize the added investment, if any.

    Technology types (resource)

    Manufacturers of products certified by the Air-conditioning and Refrigeration Institute (ARI) Standard 330 for ground source closed-loop heat pump equipment, publish a capacity rating for each model cataloged at the standard entering water rating conditions of both 77 ° F for cooling and 32 ° F for heating. The cooling EER, heating COP and fluid flow for both is also published. In calculating the cooling Standard Energy Efficiency Rating (EER) and the heating Coefficient of Performance (COP), a penalty for the water pump effect of 0.8 watts per gallon per minute per foot of head is added to the measured power input. This approximates a 25% total pump efficiency. Further more, a 17 foot pressure drop shall be added for the loop to determine the total pressure drop of the system for the pumping penalty.

    You should not confuse the ARI Standard Energy Efficiency Rating with the expression SEER. The latter stands for Seasonal Energy Efficiency Ratio. SEER is a measure of seasonal cooling efficiency under a range of weather conditions, assumed to be typical for a location, and of performance losses due to cycling under part load conditions. Most manufacturers publish performance ratings on their various models. These ratings are usually specified by a model number at a fixed air flow in cubic feet per minute (cfm) with the following variables:

    • Several fluid flow rates in gallons per minute,
    • Entering fluid temperatures from 25 to 100 ° F,
    • Entering air temperatures at 80 ° F dry bulb and 67 ° F wet bulb for cooling, and
    • Entering air at 70 ° F dry bulb for heating.

    The following rating values are given for cooling for each of the above variables: Total capacity in:

    • Btu per hour,
    • Sensible capacity in Btu per hour,
    • Heat rejection to the loop in Btu per hour,
    • Power input in watts, and
    • Energy efficiency rating (EER), which is the total capacity divided by the power input, or Btu per watt.

    Also, for each of these variables, the following rating values are given for heating:

    • Total capacity in Btu per hour,
    • Heat absorption from the loop in Btu per hour,
    • Power input in watts,
    • Coefficient of Performance (COP), which is the total capacity divided by the power input converted to Btu per hour, and multiplied by 3.412 Btu per hour per watt, and
    • Performance includes provision for an antifreeze solution used at 35 ° F and below entering water temperatures, but not the pumping penalty for the antifreeze use.
    It is important not to extrapolate from the data tables provided by manufacturers. Extrapolation removes the data from the context and boundaries of the table, and is not a good engineering practice. This is why most manufacturers say that interpolation between ratings within a table is permissible, but extrapolation is not.

    Other published data typically includes:

    • Correction factors given for various other entering air conditions, dry and wet bulb, and other air flow ratings,
    • The unit water pressure drop is also published for each flow rate, in either feet of water or pounds per square inch (psi),
    • Blower performance including fan motor brake horsepower (bhp), and external static pressure capability,
    • Electrical data on voltages and current draw,
    • Physical data including operating weight and refrigerant charge, and Hot water generating capacity.

    Efficiency

    In general, efficiency is defined as the Useful Work or Energy Delivered divided by the energy supplied to do that work. In heating and cooling with heat pumps, the definition is changed somewhat. For cooling the efficiency is expressed as the Energy Efficiency Ratio - EER.

    If the unit cooling capacity and EER is known, the kW power input can be calculated. For example, a unit having a total cooling capacity of 26,000 BTUH at an EER of 11.4, the cooling unit power input is:

    26,000 BTUH / 11.4 x 1000 watts/kW = 2.28 kW

    For heating, the efficiency is expressed as the Coefficient of Performance or COP. If the unit heating capacity and COP is known, the kW power input can be calculated. For example, a unit having a heating capacity of 33,500 BTUH at a COP of 3.9, the heating unit power input is:

    33,500 BTUH / 3.9 COP x 3,413 BTUH/kW = 2.51 kW

    Keep in mind the unit EER and COP are dependent on the entering ground water temperature, water flow rate through the unit, airflow rate and the entering air temperature. High efficiency equipment comes with a higher price tag. It is difficult to state a general rule about selecting equipment on the basis of efficiency because of the economic considerations and the merits of each system and the equipment used with it.

    Air flow is typically selected to be between 300 and 525 cfm per ton of cooling capacity. 400 cfm per ton is typical. The final selection will be governed by the sensible to total load ratio.

    Water flow through each unit should be designed to simplify water balancing. To do this, the system should be designed to keep unit water pressure drops as close as possible to each other. Though the target water temperature rise is usually 12 ° F. or 2.0 gpm per ton, they can range from 8 to 15 ° F, equal to 3 to 1.6 gpm per nominal ton of cooling capacity.

    The gpm per ton can be derived from the following formula: 12,000 divided by the result of the temperature rise, times 500. In this formula, 500 equals water at 8.33 pounds per gallon times 60 minutes per hour.


    Evaporative Cooling

    Reduce the energy consumed by mechanical cooling equipment by using the cooling effects of evaporating water.

    ec-c00114

    Evaporative cooling supply air can reduce the energy consumed by mechanical cooling equipment. The two general types of evaporative cooling are direct and indirect systems. The effectiveness of either of these methods is directly dependent on the low wet bulb temperature in the supply air stream. This is why these systems are popular in desert climates. In some applications, the two types are combined as shown here.

    Applications

    The effectiveness of either of these methods is directly dependent on the low wet bulb temperature in the supply air stream. This is why these systems are popular in desert climates.

    Technology types (resource)

    ec-c00115

    Evaporative cooling - direct

    Direct evaporative cooling introduces water directly into the supply airstream (usually with a spray or some sort of wetted media). As the water absorbs heat from the air, it evaporates. While this process lowers the dry bulb temperature of the supply airstream, it also increases its wet bulb temperature by raising the air moisture content.

    ec-c00116

    While an evaporative cooling system can effectively reduce the required capacity of the mechanical cooling equipment, it usually does not eliminate the need for a conventional cooling coil (except in certain arid regions of the country). Additional static pressure typically around 0.2 to 0.3 inches water column is required by the air handling system whenever evaporative coils are used in conjunction with a conventional cooling coil.

    Evaporative cooling - indirect

    ec-c00117

    Indirect evaporative cooling uses an additional waterside coil to lower supply air temperature. The added coil is placed ahead of the conventional cooling coil in the supply airstream, and is piped to a cooling tower where the evaporative process occurs. Because evaporation occurs elsewhere, this method of "pre-cooling" does not add moisture to the supply air, but is less effective than direct evaporative cooling. That is, it will not cool air to as low a temperature at the same outside air wet bulb.

    ec-c00118

    Thermal Storage

    Cut energy dollars by shifting peak cooling energy demands to off-peak hours when rates are lower.

    Thermal storage (hot or cold) is a cost saving technique, and in some cases, energy saving technology. Commercial cooling can account for as much as 40% of peak demand on a hot summer day. Cool storage can shift some or all of the on-peak demand to off-peak hours. With cool storage (chilled water or ice storage), cost is saved by:

    • Reducing electric demand charges through decreasing or eliminating chiller operation during peak demand periods
    • Operating chillers at night and displacing energy use from peak to off-peak periods when the energy is at a lower cost.

    Hot water storage for domestic service water is a common example. It assures a supply during peak occupant demand times, and reduces cost in the same manner as cool storage. Storing hot water for space heating is less common, except where electric energy is used for heating.

    Advantages

    There are a number of advantages for users, specifiers, and utilities:

    • Users gain by reducing their utility bills - largely through peak-shaving; reduced equipment size, space and weight; reduced compressor kW due to operating at more hours at full load and at nighttime lower condensing temperatures; availability of cold air distribution when ice is used; possible backup cooling or heating redundancy in event of power failure; when chilled water storage is used, availability of an added fire-protection water source.
    • Specifiers gain from cool storage being a proven technology whose use can differentiate their projects from those of others.
    • The utilities can gain from reduced peak use, improved load factors, added off-peak sales, deferred peak-capacity expansion costs, and improved competitive position over gas-fired alternatives.

    Disadvantages

    • May increase first cost of HVAC system,
    • More complicated system design,
    • Requires well-trained maintenance crew,
    • Possible ambient heat gain to storage tanks.
    • Specifying engineer has little incentive to use as it costs more to design and the firm may have little or no experience with the technology.
    • Some of the risks include night-time loads greater than planned, insufficient storage provided so on hot days demand is not saved, improper controls supplied, operator inattention or unskilled, condensation on ducts with low temperature supply air when a fan is out of service.

    Applications

    Cooling, not heating, is a main concern of commercial building owners. Many buildings are populated with people, heat-emitting office and production equipment, and ample lighting — all generating so much heat that cooling is required during most of the working hours all year. Most of these hours occur during the peak hours defined by the electric rate structure. Cool storage can shift all or most of this use to lower-cost off-peak hours resulting in lower operating cost without sacrificing comfort...and in some cases, increasing comfort.

    Best applications

    The best cool storage applications are in any building:

    • being charged on a time-of-use electric rate schedule
    • having high on-peak demand charges, with relatively low or no off-peak demand charge
    • that has peak cooling loads during utility on-peak hours
    • has very few comfort or process cooling hours per day, week or month, but with high peak loads during those few hours (such as churches).
    • requiring low humidity control where ice storage can be used.

    Air conditioning applications that can best benefit are office buildings, schools and college buildings, religious institutions, laboratories, large retail stores, libraries, museums, and the public use areas (meeting rooms, exhibit halls, convention centers) of hotels and public assembly buildings.

    Possible applications

    Other applications include:

    • Industrial processes with batch cooling requirements
    • Facilities where low humidity can be achieved with the low water temperature achieved from ice storage
    • Buildings where space is at such a premium that the small ducts used with low air temperature distribution are advantageous, such as retrofit of older, historic buildings.
    • Facilities where the cold storage can be tied into existing ammonia or other refrigeration systems.

    Technology types (resource)

    Depending on the needs of the building or process and the electric rate structure, there are several types of cool storage designs that may be employed on a given project:

    • Full storage (load shifting)- discharging stored capacity without any concurrent chiller operation
    • Partial storage (load leveling)- discharging storage to meet cooling loads with concurrent operation of some chiller(s) piped in parallel with storage).
    • Full recharge - recharging storage with chiller operation
    • Partial recharge - recharging storage with chiller capacity while simultaneously providing capacity to the cooling load.
    • Standby - no normal use of storage, with chillers serving the cooling loads as they would in the absence of storage. Storage used when power outages occur.

    Storage capacity is usually defined in ton-hours which is the sum of the actual tons required each hour for the design day. It can be achieved using either chilled water storage or ice storage. Chilled water storage typically requires more space (½ to 1 gal per sq ft of conditioned space) than ice storage (1/16 to _ gal).


    Low Temperature Air Conditioning

    Reduce initial cost, electrical demand, and operating costs through this system's smaller fans and ductwork.

    General

    Low temperature primary air systems provide 42¡F to 48¡F supply air for comfort cooling. The principal advantages of this air delivery option over conventional systems include lower first cost, lower electrical demand and reduced operating costs.

    The smaller fans and ductwork diameters required for low temperature air systems not only reduce equipment costs, but also offer the potential for architectural savings, since less floor-to-floor height is needed. And because the fans and pumps used require less horsepower, the system consumes less energy than many traditional types of air delivery.

    Low temperature supply air also improves comfort levels by reducing the relative humidity in the occupied space. This reduction in humidity often results in a perceived improvement in indoor air quality. In addition, occupants tend to desire warmer space temperatures which can lead to additional energy savings. Typical room conditions for a low temperature primary air system are 78¡F with a relative humidity of 35 to 45 percent.

    Proper care must be taken to ensure that condensate does not develop on the ductwork or terminal units. Selection of air diffusers is of particular importance to ensure adequate distribution at lower airflow volumes. And, particular care must be taken to assure required air changes for adequate ventilation (i.e., outside air at modulated conditions), as well as for smoke pressurization strategies.

    Advantages

    • The principal advantages of this air delivery option over conventional systems include lower first cost, lower electrical demand and reduced operating costs.
    • The smaller fans and ductwork diameters required for low temperature air systems not only reduce equipment costs, but also offer the potential for architectural savings, since less floor-to-floor height is needed. And because the fans and pumps used require less horsepower, the system consumes less energy than many traditional types of air delivery.
    • Low temperature supply air also improves comfort levels by reducing the relative humidity in the occupied space.

    Disadvantages

    • Because of delivery of low supply air, the unit efficiencies are generally lower.
    • If the ducts are not well insulated, a condensate dripping problem may occur.

    Heating systems provide space heating, water heating (domestic, swimming pool, etc.), sterilization, and other process heating needs. These systems are often combined with space cooling systems. Heating can be accomplished using electric and fossil fuel sources.

    There are three basic heating system designs:

    electric resistance, fuel fired, and heat pump systems.

    • Electric resistance systems convert electricity to heat directly, with almost 100 percent efficiency.
    • Fuel-fired systems burn fuels in a boiler or heater under careful air/fuel control. The heat of combustion is recovered in some form of integral heat exchange to heat water, steam, or air.
    • Heat pumps recover and reuse energy by raising the temperature of the waste heat (i.e. water, outdoor or exhaust air, etc.) so that it can be reused. This heat is recovered in some form of integral heat exchange to heat water or air.
    • Electric resistance heating is generally the least expensive to install, simplest to install and operate, and safer than fuel-fired systems. But heat pumps are much more efficient and cost-effective alternative to electric resistance systems.

    This page provides summarized descriptions of numerous space heating methods. Click one of the following to jump to a particular method:



    Advantages of Electric Heat

    Lower equipment and maintenance costs, safety and cleanliness are among the advantages of electric heat.

    Electric heating equipment is usually less expensive to install than fuel-fired systems. Where heating is infrequent (such as with buildings with high internal gains), the annual operating costs may be low as well. Where hours of use could be significant, increases in building insulation may prove desirable since operating savings usually provide an adequate financial offset.

    Electric heat - comfort-flexibility

    Each area can be heated independently and controlled with individual thermostats. Additional areas that may be added in the future can be heated without expensive heating plant expansion. Year-round comfort is improved as a result of increased insulation.

    Electric heat building cost

    Elimination of boiler, boiler room chimney, and fuel tanks, and the saving of valuable floor space reduces initial construction cost.

    Electric heat safety

    The danger of explosion, asphyxiation, and fuel leakage is eliminated.

    Electric heat maintenance

    No boiler cleaning pump replacements or possible freeze ups from boiler breakdowns. It may also be possible to eliminate the requirement of operating engineers in some areas.

    Electric heat - cleaner

    The elimination of flue, smoke and fumes reduces cleaning costs, janitorial expenses and redecorating costs.


    Unitary Heat Pumps

    Year-round temperature control with the added feature of zone control.

    Unitary heat pumps are factory-packaged refrigerant-based heat pumps that are available in a number of application categories which include:

  • Packaged terminal heat pumps (PTHP)
  • Closed water loop heat pump systems
  • Ground-Coupled (Closed-Loop) Systems
  • Ground water-source heat pumps
  • Large unitary air- and water-source heat pumps
  • In each category there are several possible configurations, including:

    • Single package, with all components in a single enclosure
    • Roof-top packages - a variation on the single package
    • Split units, with remote outdoor coil, fan, and/or compressor
    • Air and water-source heat pumps
    • Heating only heat pumps

    Package units and the indoor sections of split units are available in several configurations:

    • Vertical for closet installations,
    • Console for installation under windows, and
    • Horizontal for ceiling or outdoor locations.

    Some models have decorative casings. Others can be built-in. With the exception of large unitary heat pumps, the units are designed for free-air delivery or with short duct connections between the unit and the conditioned space. Most heat pump manufacturers participate in the Air-Conditioning and Refrigeration Institute (ARI) Certification Program. Product performance (below 135,000 BTUH sizes) is listed in the ARI Directory of Certified Products. This allows a performance comparison of various models from various manufacturers. Sizes range from l/2-ton package terminal heat pumps up to rooftop units of 30-tons or more. Many are provided with supplemental electric heaters to satisfy the load when the outdoor temperatures drop below the set point. Gas fired supplemental heat is also available in a limited range of equipment. Most heat pumps are sold and installed by local air conditioning contractors, who also provide routine service and repair. Depending on the nature of the application, this availability of fast service can be very important in equipment selection.

    Advantages

    Unitary heat pumps

    • They provide individual temperature control in small occupied zones during nights and weekends without the need for a large central plant chiller or boiler and their associated pumps,
    • The heat pump's consumption of electricity can be separately metered.

    Water loop heat pumps

    • They don't require wall openings to reject heat from air-cooled condensers,
    • They aren't exposed to the weather and therefore tend to have a longer service life,
    • If a unit fails, the entire system doesn't shut down, however, failure of a loop pump, heat rejection device or secondary heater can affect the entire system.

    Disadvantages

    • Imprecise temperature and humidity control,
    • In-room or in-space maintenance including frequent filter replacement,
    • Water loop systems require regular loop maintenance, and
    • These systems require space for pumps heat exchangers and boilers (if a boiler is required).

    Applications

    Unitary heat pumps can provide year-round electric air conditioning at a competitive cost with the feature of individual room or zone control. They can be used in almost any type room or building. They can be used in a variety of engineered system arrangements (i.e. closed water loop, etc.) to provide economic operating costs and desired features (night setback, etc.) not available in other systems.

    Best applications

    They are best applied:

    • Where there aren't competitive alternative heating energy sources,
    • In climatic areas with moderate heating loads, and
    • Where individual room or zone control is required for customer satisfaction. They offer the most advantages when combined in any of the many available engineered system arrangements.

    Possible applications

    Unitary heat pumps can be applied in almost any building as they are extremely versatile. The basic customer decision is whether the requirements of a particular application can be best served by unitary system or by a central chilled water system. The required features, floor space and weight, ceiling height, cost factors, maintenance factors, operational factors all need to be considered and evaluated.

    Technology types (resource)

    Unitary air and water source heat pumps are available as larger capacity commercial self-contained units which serve large zones using ducts for air distribution. Air source units must be located along outside walls or on the roof. They tend to have higher operating costs than central plants or water-source heat pumps.

    • Water-source units can be located anywhere but require ventilation air ducts. They are usually connected to a cooling tower circuit for heat rejection when they are in the cooling mode, and to a central hot-water heater or strip heater when heating is required. Advantages include low first cost and the availability of optional accessories (variable air volume control, economizer cycle, night setback and morning warm-up).
    • Large system heat pump applications are often applied in, buildings using two- or four-pipe water distribution systems, or in industrial applications. Many large buildings require cooling the year-round due to large internal loads from lighting, electronic and other business equipment. Only the perimeter zones of these structures ever need heating. The warm condenser water from the water chillers serving this cooling load can be used as a heat source. The water-to-water heat pump is piped in a cascade system, using this waste heat to preheat domestic hot water or provide hot water to satisfy building space or reheat loads. Units are available to heat water from 105°F to 120°F, or even higher if needed. The lower the hot water temperature required, the lower the energy consumption.
    • In some cases, the units are combined into a single heat recovery chiller with a double-bundle condenser. The house water condenser serves the hot water loop for the building. When the waste heat exceeds the heat requirement, the excess heat is rejected in the second tower water condenser. Thermal storage can also be integrated into this system. Other options include integration with closed loop water-to-air heat pumps, or secondary heat recovery from water loop heat pump systems.
    • Air-to-water heat pumps perform in a similar manner but typically use warm exhaust air as the heat source. They are often referred to as heat pump water heaters and are used in hotels, restaurants, laundries and other applications needing a lot of hot water.
    • Many industrial processes have low-level waste heat that must be rejected. Factory-packaged, closed-cycle refrigerant-based heat pumps are available to heat water to 120°F or warmer. Using waste heat for this purpose off-loads cooling towers or evaporative condensers while reducing boiler fuel consumption and the corresponding products of combustion.

    Efficiency

    Most heat pump manufacturers rate their equipment in accordance with ARI standards and participate in the ARI certification programs. ARI Standard 210/240 covers air-source units, ARI Standard 330 covers ground source closed loop heat pumps, ARI Standard 325 covers ground water-source heat pumps, ARI Standard 310/380 covers packaged terminal heat pump air-source units, and ARI Standard 320 covers water-source heat pumps.

    Packaged terminal heat pumps typically have cooling energy efficiency ratios (EER) in the range of 9.0 to 11.0 Btu per watt of electrical energy input and a heating coefficient of performance (COP) in the range of 2.7 to 3.3 .

    Air-source heat pumps typically have cooling seasonal energy efficiency ratios (SEER) in the range of 10.0 to 14.0 Btu per watt of electrical energy input and a heating seasonal performance factor (HSPF) in the range of 6.0 to 9.0 Btu per watt of electrical energy input.

    Water-source heat pumps typically have cooling energy efficiency ratios (EER) in the range of 10.0 to 15.0 Btu per watt of electrical energy input and a heating coefficient of performance (COP) in the range of 3.7 to 5.2.

    Refer to the segment on ground coupled and ground source heat pumps for a discussion on the efficiency of these heat pumps.


    Ground Water Source (Open Loop) Heat Pump Systems

    A low-energy and maintenance cost system that can use either a surface or underground water source as the heat source and sink.

    An open-loop, ground-water heat pump, uses a surface or underground water source (such as a lake, river, or well) as the heat source and sink. Well water designs are the most common and seem to be the most cost effective. The well supplies both domestic water and water for the heat pump. Approximately three gallons per minute of well water are needed per ton of cooling capacity.

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    Ground water source open-loop heat pumps use the same concept as the ground coupled units - for example, in the Midwest the temperature of the earth near the surface and the water in it (aquifer) is typically around 55°F. Water is taken from the ground or surface water (pond, lake, etc.), circulated to the individual heat pumps and the returned to the ground via a disposal well, returned to the lake or pond, or where permitted discharged into a stream or river.

    When more units are heating than cooling the circulating water temperature drops prior to disposal. Conversely, when more units are cooling than heating, the circulating water is warmed prior to disposal.

    Advantages

    In both commercial and residential installations, geothermal heat pump systems typically have lower maintenance costs than conventional systems as all equipment is installed inside the building or underground. This means that there is no outside equipment exposed to weather and vandalism. All refrigerant systems are sealed, similar to household refrigerators.

    • Open loop systems have less loss in heat transfer
    • Open loop systems have lower heat pump energy costs
    Geothermal systems are very flexible. They can be easily and inexpensively subdivided or expanded to fit building remodeling or additions. They are particularly well-suited to "tenant finish" installations.

    In commercial installations, systems can save money by recovering excess heat from building interior zones and moving it to the perimeter of the building. They can also save money by allowing management to isolate and shut down unoccupied areas of the building.

    Disadvantages

    • Problems associated with disposal of the water after once-through the heat pump, disposal wells can be costly,
    • Water which has suitable qualities could change with time to poor quality that causes problems of corrosion later in time,
    • Costs associated with the drilling of the water well can be high and unknown at the outset,
    • Water tables and well output can change over time and cause future problems,
    • Permitting and its costs are usually required,
    • Open-loop systems have more potential problems than either conventional systems or closed-loop geothermal systems because they bring outside water into the unit. This can lead to clogging, mineral deposits, and corrosion in the system.
    • Open-loop systems require a large supply of clean water in order to be cost effective. This often limits their use to coastal areas, and areas adjacent to lakes, rivers, streams, etc. In addition, there must be an acceptable method of returning the used water to the environment. This may be limited not only by environmental factors (such as no place to dump that much water), but also by local and state regulations.
    • Since accessibility to terminal units is important in geothermal systems, architects and mechanical and structural designers must carefully coordinate their work.
    • Each unit requires both electrical and plumbing service.
    • Duct systems must be installed to bring outside air to each space.
    • Secondary or backup heat sources are required in cooler climates.

    Applications

    Open loop heat pumps can be applies wherever there is an ample source of good quality water is available along with an adequate and permitted disposal method.

    Best applications

    Best Applications Where water supply and quality is known and water use is not now, or expected to be, regulated; and where a closed loop system may not be applicable.

    Technology types (resource)

    Manufacturers of products certified by the Air-conditioning and Refrigeration Institute (ARI) Standard 325 for ground water-source heat pump equipment publish a capacity rating for each model catalogued at the standard entering water rating conditions of both 70 and 50°F for cooling and heating. The cooling EER, heating COP and water flow for both is also published. In calculating the cooling Standard Energy Efficiency Rating (EER) and the heating Coefficient of Performance (COP), a water pump penalty effect is added to the measured power input.

    You should not confuse the ARI Standard Energy Efficiency Rating with the expression SEER. The latter stands for Seasonal Energy Efficiency Ratio. SEER is a measure of seasonal cooling efficiency under a range of weather conditions, assumed to be typical for a location, and of performance losses due to cycling under part load conditions.

    Most manufacturers publish performance ratings on their various models. These ratings are usually specified by a model number at a fixed air flow in cubic feet per minute (cfm) with the following variables:

    • Several fluid flow rates in gallons per minute,
    • Entering water temperatures from 35 to 100°F,
    • Entering air temperatures at 80°F dry bulb and 67°F wet bulb for cooling, and
    • Entering air at 70°F dry bulb for heating.

    The following rating values are given for cooling for each of the above variables:

    • Total capacity in Btu per hour,
    • Sensible capacity in Btu per hour,
    • Heat rejection to the water in Btu per hour,
    • Power input in watts, and
    • Energy efficiency rating (EER), which is the total capacity divided by the power input, or Btu per watt.

    Also, for each of these variables, the following rating values are given for heating:

    • Total capacity in Btu per hour,
    • Heat absorption from the water in Btu per hour,
    • Power input in watts,
    • Coefficient of Performance (COP), which is the total capacity divided by the power input converted to Btu per hour, and multiplied by 3.412 Btu per hour per watt.
    It is important not to extrapolate from the data tables provided by manufacturers. Extrapolation removes the data from the context and boundaries of the table, and is not a good engineering practice. This is why most manufacturers say that interpolation between ratings within a table is permissible, but extrapolation is not.

    Other published data typically includes:

    • Correction factors given for various other entering air conditions, dry and wet bulb, and other air flow ratings,
    • The unit water pressure drop is also published for each flow rate, in either feet of water or pounds per square inch (psi),
    • Blower performance including fan motor brake horsepower (bhp), and external static pressure capability,
    • Electrical data on voltages and current draw,
    • Physical data including operating weight and refrigerant charge, and Hot water generating capacity.

    Efficiency

    In general, efficiency is defined as the Useful Work or Energy Delivered divided by the energy supplied to do that work. In heating and cooling with heat pumps, the definition is changed somewhat. For cooling the efficiency is expressed as the Energy Efficiency Ratio - EER.

    If the unit cooling capacity and EER is known, the kW power input can be calculated. For example, a unit having a total cooling capacity of 26,000 BTUH at an EER of 11.4, the cooling unit power input is:

    26,000 BTUH / 11.4 x 1000 watts/kW = 2.28 kW

    For heating, the efficiency is expressed as the Coefficient of Performance or COP. If the unit heating capacity and COP is known, the kW power input can be calculated. For example, a unit having a heating capacity of 33,500 BTUH at a COP of 3.9, the heating unit power input is:
    33,500 BTUH / 3.9 COP x 3,413 BTUH/kW = 2.51 kW

    Keep in mind the unit EER and COP are dependent on the entering ground water temperature, water flow rate through the unit, airflow rate and the entering air temperature. High efficiency equipment comes with a higher price tag. It is difficult to state a general rule about selecting equipment on the basis of efficiency because of the economic considerations and the merits of each system and the equipment used with it.

    Air flow is typically selected to be between 300 and 525 cfm per ton of cooling capacity. 400 cfm per ton is typical. The final selection will be governed by the sensible to total load ratio.

    Water flow through each unit should be designed to simplify water balancing. To do this, the system should be designed to keep unit water pressure drops as close as possible to each other. Though the target water temperature rise is usually 12°F. or 2.0 gpm per ton, they can range from 8 to 15°F, equal to 3 to 1.6 gpm per nominal ton of cooling capacity.

    The gpm per ton can be derived from the following formula: 12,000 divided by the result of the temperature rise, times 500. In this formula, 500 equals water at 8.33 pounds per gallon times 60 minutes per hour.

    Contact us for a detailed list of manufacturers for this equipment.


    Ground-Coupled (Closed Loop) Systems

    These reliable and cost-effective systems utilize the temperature of the earth near the surface, but differ from closed-loop systems because no water is taken from the ground or disposed of.

    Ground source closed-loop heat pumps use the same concept as the ground source open-loop units - the temperature of the earth near the surface is typically around 55 ° F. The difference is no water is taken from the ground or disposed of. The water is circulated to the individual heat pumps and the returned to a ground closed-loop to be cooled or warmed.

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    When more units are heating than cooling the circulating water temperature drops and is warmed back up by the earth in the ground heat exchanger. Conversely, when more units are cooling than heating, the circulating water is cooled down by the ground heat exchanger buried in the earth.

    The closed-loop ground-coupled system uses a buried or submerged geothermal heat exchanger. This heat exchanger can reject or draw heat from a source such as the earth, a lake, or a pond, by circulating water through a closed-loop. This heat exchange loop may be pipe coils installed horizontally, vertically (down-hole), in a coil, or in other configurations. The down-hole system is used when surface area is limited since horizontal or even spiral coils can take up a lot of room and run up excavation costs.

    Advantages:

    • Geothermal heat pump systems have lower operating costs, lower maintenance costs, lower life cycle costs, increased reliability, and greater comfort than alternative cooling and heating systems.
    • There is no outside equipment exposed to weather and vandalism, and no exposed equipment where children can get hurt.
    • In both commercial and residential installations, geothermal heat pump systems typically have lower maintenance costs than conventional systems as all equipment is installed inside the building or underground. All refrigerant systems are sealed, similar to household refrigerators.
    • Geothermal systems are very flexible. They can be easily and inexpensively subdivided or expanded to fit building remodeling or additions. They are particularly well-suited to "tenant finish" installations.
    • In commercial installations, systems can save money by recovering excess heat from building interior zones and moving it to the perimeter of the building. They can also save money by allowing management to isolate and shut down unoccupied areas of the building.
    • Since units can be installed in a portion of an equipment room or small closet, it gives owners more usable space.
    • In retrofit situations, they can replace rooftop equipment or a central chiller and boiler.
    • Industry standards, set by the Air-Conditioning and Refrigeration Institute, provide consumers with easy to find and consistent support in choosing equipment. They establish standards for testing and rating products, and certify the performance ratings that participants publish.
      Geothermal heat pump systems have lower operating costs, lower maintenance costs, lower life cycle costs, increased reliability, and greater comfort than alternative cooling and heating systems.
    • There is no outside equipment exposed to weather and vandalism, and no exposed equipment where children can get hurt.
    • In both commercial and residential installations, geothermal heat pump systems typically have lower maintenance costs than conventional systems as all equipment is installed inside the building or underground. All refrigerant systems are sealed, similar to household refrigerators.
    • Geothermal systems are very flexible. They can be easily and inexpensively subdivided or expanded to fit building remodeling or additions. They are particularly well-suited to "tenant finish" installations.
    • In commercial installations, systems can save money by recovering excess heat from building interior zones and moving it to the perimeter of the building. They can also save money by allowing management to isolate and shut down unoccupied areas of the building.
    • Since units can be installed in a portion of an equipment room or small closet, it gives owners more usable space.
    • In retrofit situations, they can replace rooftop equipment or a central chiller and boiler.
    • Industry standards, set by the Air-Conditioning and Refrigeration Institute, provide consumers with easy to find and consistent support in choosing equipment. They establish standards for testing and rating products, and certify the performance ratings that participants publish.

    Disadvantages

    • Geothermal heat pump systems may require a higher initial investment to cover the incremental cost of the ground loop.
    • Space is required for installing the ground loop,
    • They require a knowledgeable contractors to assure correct installation, check-out, start-up and operation.
    • Since accessibility to terminal units is important in geothermal systems, architects and mechanical and structural designers must carefully coordinate their work.
    • Each unit requires both electrical and plumbing service.
    • Duct systems must be installed to bring outside air to each space.
    • Secondary or backup heat sources, and use of a loop anti-freeze solution, are required in cooler climates.

    Applications

    Closed-loop heat pumps can be applied wherever there is space to install the horizontal, vertical or other configuration ground loop. Current installations range from small residences to schools and large commercial or institutional buildings.

    Commercial Application Benefits In addition to the general benefits of a geothermal system, there are other advantages for the commercial user to install a geothermal heat pump system.

    Efficiency

    In the heating mode the geothermal heat pump system extracts two-thirds or more of its energy from the earth and moves it to the heat pump unit. Only one-third of the energy needed is purchased power. This is used to run the compressor, circulating pumps and fan.

    In the cooling mode, the unwanted heat is transferred back into the earth for reuse in heating.

    No ground level outdoor equipment

    All of the equipment needed can be installed in one or more mechanical equipment rooms, above dropped ceilings, or on the roof. Except where roof-top units are installed, there are no visible outdoor units to suffer from deterioration due to weather or vandalism, and no outdoor noise. The rest of the equipment consists of an array of piping buried beneath the ground. These pipes can be installed in a vertical well system, horizontally buried under the surface, or installed in a pond. In some cases, well or pond water can be used directly without buried pipe.

    Environmental

    Geothermal heat pump systems produce no on-site pollutants, improve indoor air quality, and reduce the amount of pollutants at the generating station when compared to other forms of electric heat. They also result in lower carbon dioxide emissions which reduces the threat of global warming.

    Service hot water

    In cooling mode, the unwanted heat can be used to preheat hot water at a very low operating cost. In winter, surplus heat can be used in the same way.

    Warmer air distributed during heating

    No more seemingly cold drafts from the air outlets often encountered with conventional heat pumps.

    No supplemental heat

    Most geothermal systems can operate year-round without supplemental direct heat.

    Little or no out-of-pocket incremental cost

    Any added initial cost can often be included in the project financing, and the operating cost savings used to amortize the added investment, if any.

    Technology types (resource)

    Manufacturers of products certified by the Air-conditioning and Refrigeration Institute (ARI) Standard 330 for ground source closed-loop heat pump equipment, publish a capacity rating for each model cataloged at the standard entering water rating conditions of both 77 ° F for cooling and 32 ° F for heating. The cooling EER, heating COP and fluid flow for both is also published. In calculating the cooling Standard Energy Efficiency Rating (EER) and the heating Coefficient of Performance (COP), a penalty for the water pump effect of 0.8 watts per gallon per minute per foot of head is added to the measured power input. This approximates a 25% total pump efficiency. Further more, a 17 foot pressure drop shall be added for the loop to determine the total pressure drop of the system for the pumping penalty.

    You should not confuse the ARI Standard Energy Efficiency Rating with the expression SEER. The latter stands for Seasonal Energy Efficiency Ratio. SEER is a measure of seasonal cooling efficiency under a range of weather conditions, assumed to be typical for a location, and of performance losses due to cycling under part load conditions. Most manufacturers publish performance ratings on their various models. These ratings are usually specified by a model number at a fixed air flow in cubic feet per minute (cfm) with the following variables:

    • Several fluid flow rates in gallons per minute,
    • Entering fluid temperatures from 25 to 100 ° F,
    • Entering air temperatures at 80 ° F dry bulb and 67 ° F wet bulb for cooling, and
    • Entering air at 70 ° F dry bulb for heating.

    The following rating values are given for cooling for each of the above variables: Total capacity in:

    • Btu per hour,
    • Sensible capacity in Btu per hour,
    • Heat rejection to the loop in Btu per hour,
    • Power input in watts, and
    • Energy efficiency rating (EER), which is the total capacity divided by the power input, or Btu per watt.

    Also, for each of these variables, the following rating values are given for heating:

    • Total capacity in Btu per hour,
    • Heat absorption from the loop in Btu per hour,
    • Power input in watts,
    • Coefficient of Performance (COP), which is the total capacity divided by the power input converted to Btu per hour, and multiplied by 3.412 Btu per hour per watt, and
    • Performance includes provision for an antifreeze solution used at 35 ° F and below entering water temperatures, but not the pumping penalty for the antifreeze use.
    It is important not to extrapolate from the data tables provided by manufacturers. Extrapolation removes the data from the context and boundaries of the table, and is not a good engineering practice. This is why most manufacturers say that interpolation between ratings within a table is permissible, but extrapolation is not.

    Other published data typically includes:

    • Correction factors given for various other entering air conditions, dry and wet bulb, and other air flow ratings,
    • The unit water pressure drop is also published for each flow rate, in either feet of water or pounds per square inch (psi),
    • Blower performance including fan motor brake horsepower (bhp), and external static pressure capability,
    • Electrical data on voltages and current draw,
    • Physical data including operating weight and refrigerant charge, and Hot water generating capacity.

    Efficiency

    In general, efficiency is defined as the Useful Work or Energy Delivered divided by the energy supplied to do that work. In heating and cooling with heat pumps, the definition is changed somewhat. For cooling the efficiency is expressed as the Energy Efficiency Ratio - EER.

    If the unit cooling capacity and EER is known, the kW power input can be calculated. For example, a unit having a total cooling capacity of 26,000 BTUH at an EER of 11.4, the cooling unit power input is:

    26,000 BTUH / 11.4 x 1000 watts/kW = 2.28 kW

    For heating, the efficiency is expressed as the Coefficient of Performance or COP. If the unit heating capacity and COP is known, the kW power input can be calculated. For example, a unit having a heating capacity of 33,500 BTUH at a COP of 3.9, the heating unit power input is:

    33,500 BTUH / 3.9 COP x 3,413 BTUH/kW = 2.51 kW

    Keep in mind the unit EER and COP are dependent on the entering ground water temperature, water flow rate through the unit, airflow rate and the entering air temperature. High efficiency equipment comes with a higher price tag. It is difficult to state a general rule about selecting equipment on the basis of efficiency because of the economic considerations and the merits of each system and the equipment used with it.

    Air flow is typically selected to be between 300 and 525 cfm per ton of cooling capacity. 400 cfm per ton is typical. The final selection will be governed by the sensible to total load ratio.

    Water flow through each unit should be designed to simplify water balancing. To do this, the system should be designed to keep unit water pressure drops as close as possible to each other. Though the target water temperature rise is usually 12 ° F. or 2.0 gpm per ton, they can range from 8 to 15 ° F, equal to 3 to 1.6 gpm per nominal ton of cooling capacity.

    The gpm per ton can be derived from the following formula: 12,000 divided by the result of the temperature rise, times 500. In this formula, 500 equals water at 8.33 pounds per gallon times 60 minutes per hour.


    Ground Source (Refrigerant Loop) Heat Pump Systems

    A similar system to ground coupled units, using a refrigerant rather than water to circulate to the individual heat pumps. These systems are potentially more efficient than water loop systems.

    Ground source closed-refrigerant-loop heat pumps use the same concept as the ground coupled units. For example, in the Midwest the temperature of the earth near the surface is typically around 55°F. With ground coupled systems water is taken from the ground or surface water (pond, lake, etc.), circulated to the individual heat pumps and the returned to the ground. With refrigerant loop systems a refrigerant such as R-22 is substituted for the water.

    The Refrigerant Loop or Direct Expansion system circulates refrigerant, instead of water or antifreeze. The refrigerant is circulated in copper piping buried in the ground, rather than plastic piping. These systems are potentially more efficient than water loop systems.

    Advantages

    • Fewer feet per ton of buried piping are needed since copper is a better conductor of heat than plastic.
    • No freeze protection problem since no water or antifreeze is required.
    • Heat is transferred directly from the refrigerant to the earth. There is no loss of efficiency due to the lower refrigerant temperature needed to first transfer heat into the water and then into the ground.
    • Many contractors have well-developed skills with copper pipe.
    • No fusion techniques are required.
    • No purge and flush operations are required.
    • No circulating pumps are needed, and
    • The system has lower operating costs.

    Disadvantages

    • Refrigerant management and oil return is important. The length of the copper piping is limited in order to achieve oil return and to minimize the refrigerant pressure drop losses. This precludes its application to many commercial buildings.
    • Environmental issues related to the system's use of more refrigerant than the water loop systems.
    • Corrosion issues, since the copper piping needs anodic protection and can be harmed by acidic soil conditions which can develop over time.
    • Operating with too low a refrigerant temperature in winter can freeze the ground and reduce heat transfer.
    • Operating with too high a refrigerant temperature in summer can bake the ground and reduce heat transfer.
    • Industry acceptance with comparatively few products available, no ARI standard, and few experienced contractors.

    These systems are in the field development stage and will not be addressed any further.

    Contact us for a detailed list of manufacturers for this equipment.


    Electric Infrared Space Heating

    Infrared (IR) space heating utilizes electromagnetic radiation to heat objects in the space, which, in turn, heats the space.

    infrared

    Heat is transferred in three ways: convection, conduction, and radiation. In most space heating systems, convection and conduction are the principle heat transfer mechanisms. Infrared (IR) space heating is accomplished through electromagnetic radiation. Natural gas, propane, and electricity are the fuels commonly used by IR heaters. Although these heaters are commonly referred to as "space heaters," they do not directly heat the space: they heat the objects in the space, which, in turn, eventually heat the space. The term "infrared space heating" is used to distinguish comfort heating from IR process heating.

    Electric IR heaters have two basic components: an IR heating element and a reflector. The IR heating element is composed of a resistor material (or radiator) that gives off electromagnetic energy in the IR portion of the spectrum when excited by an electric current. The resistor material is partially enclosed in the reflector, a fixture that reflects the radiation toward the people to be heated. Resistor materials include tungsten wire in a quartz tube, nickel chromium alloy in a quartz tube, tungsten wire in a reflector lamp, and nickel chromium alloy in a metal rod. In space heating applications, the IR radiation is normally directed toward the people in the area. However, the radiation also strikes objects, such as the floors, walls, equipment, and furnishings. These objects then retransmit the heat they receive, Through secondary, conduction, convection, and radiation. In this way, IR heaters can be used to warm the air in a room to a set temperature, much like a conventional heating system.

    Tungsten wires in quartz lamps and reflector lamps operate at filament temperatures of about 4050°F and radiate energy in the "near-infrared" portion of the spectrum. These lamps have the added advantage of providing visible light of approximately 8 lumens per watt. This can help illuminate work areas. The potential downside is that when heating is not needed, the extra light is not provided. Other lamp elements, such as metal sheath, open wire, and ribbon elements, operate between 1200 and 1800°F and emit in the "far-infrared" portion of the spectrum.

    Advantages

    • Relatively inexpensive and easy to install compared to conventional HVAC systems
    • Keeps people comfortable in relatively areas such as bus stops, covered breezeways, loading docks, outdoor restaurants, and garages.
    • Reduces the overall energy required to heat an area by allowing a background temperature of 50-60°F.
    • Simple to lay out, control, and maintain.
    • Can be used to heat "trouble spots" such as lobby areas, hallways, and entrances.
    • Less complicated than gas heating because neither gas piping nor ventilation of combustion by-products is necessary.

    Disadvantages

    • If systems are used to maintain space temperatures of 68-70°F, the overall efficiency is no better than conventional resistance heating.
    • Mounted at ceiling heights of over 30 feet, IR lamps do not keep people warm.
    • People need to be radiated from both sides to feel comfortable. That is, enough lamps must be installed to produce a criss-cross pattern.

    Best applications

    • Areas exposed to the outdoors and/or areas that require high ventilation rates.
    • The ideal application is an area maintained at 50°F in which IR heaters are used only to warm people. An example is a large warehouse watched over by a stock person near the main door. IR heaters could be installed where the stock person spends the most time, providing the stock person hearing comfort irrespective of the overall warehouse temperature.
    • Storage rooms, garages, loading docks, covered walkways, warehouses, gymnasiums, commercial/industrial plants and shops, outdoor restaurants, and store entrances.

    IR lamps and fixtures are available in a variety of shapes and sizes. They are normally hung from or attached directly to the ceiling, in a manner similar to a lighting system, with careful attention to the maximum height of forklifts, trucks, cranes, etc., that operate in the area. The IR -system designer determines the desired energy levels for the different parts of the facility and then estimates the equipment wattage required to produce the desired energy levels. The fixtures are typically available in 120-, 240-, and 480-volt systems.

    Efficiency

    The lamp efficiency depends on the material of the resistor the radiator. Clear quartz lamps have an efficiency of about 96%. Tungsten wire and quartz tubes have efficiencies of 60-80%. Metal rods have lamp efficiencies as low as 50%. The overall efficiency of the IR system depends on the type of IR element in the lamp, the absorptivity of the people, and the objects near the lamp, and the efficiency of the fixture (including the reflectivity of the reflector and the directional efficiency of the fixture). Other factors to consider in selecting an IR element include amount of visible light output, time required to develop full output, vibration resistance, and color of light. The life expectancy of any IR lamp is about 5000 or more hours.

    Contact us for a detailed list of manufacturers for this equipment.


    Hot Water & Steam Boiler Systems

    Used in many commercial buildings, the primary function of a boiler is the efficient transfer of heat from a hot combustion gas to water or steam.

    Two general categories of boilers are hot water and steam boilers. Most smaller commercial buildings use hot water boilers where water is heated to appropriate distribution temperatures (typically 140 - 180°F). These systems are often "closed" with virtually no fresh water makeup. Hot water boilers are often preferred because they normally do not need an operator or special water chemistry, and they run at higher fuel conversion efficiencies than steam boilers.

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    Steam boilers are found in many different configurations, but all serve one purpose: to contain water and transform it into steam by the application of heat. The two basic boiler designs for buildings are fire-tube and water-tube. In fire tube boilers, hot combustion gases pass through tubes submerged in water.

    In water-tube boilers, the water is contained in tubes located inside a furnace and hot flue gases pass over the tubes, heating the water, and then exit out the stack.

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    While both steam boiler designs offer comparable efficiencies, they are not interchangeable. This is primarily due to structural considerations. Because of their greater structural integrity, water-tube boilers are specified in all situations where operating pressures of 250 pounds per square inch gauge or greater are required. Individual fire-tube boilers are used in most commercial applications and are usually preferred in low-pressure applications between 3,500 (100 boiler hp) and 35,000 ( 1,000 boiler hp) pounds per hour of steam. In sizes below 3,500 Ib/hr and above 35,000 Ib/hr, water-tube units are often preferred. Whatever the design, the primary function of a boiler is the efficient transfer of heat from hot combustion gases to water or steam. To accomplish this task, three variables must be properly controlled: combustion efficiency, heat transfer and steam distribution effectiveness.

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    Contact us for a detailed list of manufacturers for this equipment.


    Electric Boilers

    Generally compact in size, electric boilers are clean-firing compared to fossil-fired boilers. Best utilized for installations requiring steam or hot water relatively few hours each year, or where a supply of gas or oil is not readily available.

    The two general categories of boilers are hot water and steam boilers. Most small commercial buildings, manufacturers, and even some food processors use hot water boilers. Water is heated to appropriate distribution temperatures, typically 140-180°F, and usually returned about 20°F lower temperature for reheat. These systems are often "closed" with virtually no fresh water make-up. Where applicable, hot water boilers are preferred because they normally do not need operators or special water chemistry. Further, since they operate at lower temperatures, hot water boilers can operate at higher fuel conversion efficiencies than steam boilers.

    Steam boilers are found in many different configurations, but all serve one purpose: to contain water and transform it into steam by the application of heat. Some boilers heat the steam even hotter than the boiling point temperature. This is referred to as superheated steam.

    Advantages

    • Clean firing - no emissions of products of combustion
    • No stack - with no combustion there is no venting or stack required
    • Highly efficient with minimum losse
    • Compact size - smaller volume and footprint than fossil fired boilers
    • Available in wide range of sizes as boiler only or in tank-type models

    Disadvantages

    Demand and energy charges can result in higher operating cost

    Applications

    Electric boilers can be applied wherever there is a need for hot water at 30 to 250 psig pressure, and steam at 15 to 250 psig pressure and in capacities up to about 3,000 kW (10 million BTUH) in a single unit with tank models up to 10,000 gallons.

    Best applications

    Installations requiring steam or hot water relatively few hours in the year; or where a supply of gas or oil is not readily available.

    Technology types (resource)

    Electric boilers typically use resistance heating elements to convert electric energy to heat energy. Heavy duty medium watt density elements with low surface temperature provide excellent protection against oxidation and scaling. Elements are operated by heavy duty UL rated magnetic contactors. Safety controls are provided including low water cutoff and temperature and pressure relief valves. A wide range of options are available including step controls, circulating packages, voltages, circuit breakers, peak load controllers, and safety interlocks.

    Efficiency

    Electric boilers are relatively 100% efficient in converting power to heat (3,412 BTUH per kW or 293 kWh per million Btu) with only a minimal percentage of radiation loss from the exposed surfaces of the boiler.

    This contrasts to fossil fuel boilers that have combustion efficiencies in the 60 to 80% range, depending on the boiler age and condition, plus other losses.

    Combustion efficiency simply indicates the flue gas loss. Boiler efficiency also includes the blowdown and standby losses. Whether comparing new or existing boilers, their most efficient operating point is usually somewhere between 60-90% load.

    However, when you are evaluating a change in steam production due to a new steam use (which would increase steam generation) or steam conservation (which would obviously reduce steam production), be very careful to consider incremental boiler efficiency.


    Heat Pumps

    Manufactured in a variety of types, a heat pump is a device that extracts heat from a source and transfers it at a higher temperature, typically for HVAC or water heating systems.

    A heat pump is a device that extracts heat from a source and transfers it at a higher temperature. While all mechanical cooling systems are technically heat pumps, in HVAC terms, "heat pump" is reserved for equipment that can heat for beneficial purposes, rather than equipment that only removes heat for cooling. Dual mode heat pumps can provide either heating or cooling, while heat-reclaim heat pumps provide heating.

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    An applied heat pump requires competent engineering for the specific application as opposed to the use of a manufacturer-designed unitary heat pump. The distinction between some models and applications can be rather fuzzy.

    Heat pumps provide an important amplification of temperature that simple heat exchangers can not do. For example, efficient heat exchangers can preheat water or air up to 2 to 5°F of the temperature of the heat source - but never as hot or hotter than the waste heat source. If a higher temperature is required, then a heat pump or a combination of heat exchanger and heat pump must be used.

    Most heat pumps used in HVAC applications today use a vapor compression cycle, similar to that used in a household refrigerator or home air conditioner and use an electric motor driven compressor, a condenser and an evaporator. Dual mode heat pumps include some form of cycle reversal where heating and cooling effects can be switched. Compressors can vary from small hermetically sealed units to large centrifugal machines. Industrial processes can be served by either this closed-vapor compression cycle, or by an open or mechanical vapor recompression or MVR cycle.

    Typical waste heat sources include outdoor or exhaust air, condenser or cooling tower water, well or other ground or surface water and heat rejected from industrial processes. The selection of the source depends on several variables such as suitability, availability, cost, and temperature. Where the source availability and the useful heat needs are not coincidental, thermal storage on either the hot or cold side should be considered.

    Advantages

    Heat pumps provide an important amplification of temperature that simple heat exchangers can not do.


    Electrical Resistance Space Heating Equipment

    Various types of space heating equipment can be used for zone controlled heating. Also an efficient method for heating spaces only occasionally used.

    Some electric resistance space heating systems permit room by room or space-by-space (zoned) control. Compared to central systems, they can afford significant energy and cost savings, particularly when spaces are used only on an occasional basis. Central heating systems must heat all spaces served to the level required by those in use. Time controls, personnel detection controls and other devices can also be employed. Typical zoned space heating equipment includes baseboard units, wall units, unit heaters, duct insert heaters, furnaces, portables, ceiling units, and insulated conductors embedded in ceiling or floor. Here are several options for electric resistance space heating.

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    Space heating equipment - wall units:

    These heaters may be flush-mounted or recessed, and use a radiant or ceramic panel, heating coils, or other form of heating clement. They come with or without a built-in fan and thermostat. These units are often used for spot heating in areas such as building entrances and where higher temperatures are needed

    0000231

    Space heating equipment - ceiling units:

    These are similar to the wall units in type, but designed for ceiling installation. Units may include lighting devices (e.g., restrooms).

    0000232

    Space heating equipment - baseboard:

    These units are installed along the base of a wall, and have relatively unrestricted length, providing a more distributed source of heat. Various types of heating elements are available in baseboard equipment.

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    Space heating equipment - deep heat system:

    These systems are used in northern climates where it may be effective to bury electric heaters in a sand bed beneath the concrete floor of the warehouse, commercial space, or garage. These large thermal masses can often be heated during the off-peak period to provide economical space heat during occupied hours. Since most people are more comfortable when their feet are warm, these systems have also been reported to provide very pleasant work environments even in the most extreme of weather conditions.

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    Space heating equipment - duct insert heater:

    Here heating elements inserted in the ducts of forced air heating systems,either at the fan location or near supply air outlets. Heaters may be step-controlled in accordance with amount of heat needed. Automatic safety cut-offs interrupt current on either over-temperature of unit or fan failure.

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    Space heating equipment - heating cable:

    These are insulated resistance heating elements manufactured in various lengths and wattage's and are suitable for installation in ceiling plaster or in/under concrete slabs. This method of heating evenly distributes the heat source and produces a low temperature radiant heat surface. This method has been used in large open buildings such as warehouses, garages, hangars, etc.

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    Space heating equipment - unit heaters:

    These heating elements are used with a fan or blower to force air into the conditioned space. Certain types are classified as heater-ventilators and perform the function of both controlled heating and ventilating. These units have been used primarily in school room heating, but can be used for many commercial/industrial applications where ventilation is required.

    Space heating equipment - infrared radiant heaters:

    These heaters generate infrared radiation, heating all objects in their "line of sight," or radiation path. Equipment is available with either metal sheath enclosed element, quartz tubes, and reflector lamps. They are all used with a directional reflector. Infrared heating is used in areas where heating the entire space through convection would be difficult or expensive in comparison to keeping people comfortable such as warehouses, garages, etc.

    Electric radiant heating panels and heating panel sets:

    These low density radiant heaters which can be mounted in wall or ceiling to provide spot heating.


    Heat Pump Desiccant

    A business case detailing how seasonal humidity interfered with production at a Swift Lumber company plant until they installed an electric-desiccant system.

    Electric desiccant heat pumps can offer an effective means of controlling space humidity. These systems use a combination of an electric vapor compression cycle as well as desiccant material, and where desiccant material is regenerated from the waste condenser heat off of the vapor compression cycle (similar to heat pump water heaters).

    Desiccant systems in HVAC applications, an alternative or supplement to traditional air conditioning systems, are used primarily where the latent load is high or where independent control of temperature and humidity is an important factor.

    Desiccants are materials which attract and hold water vapor at room temperatures and regenerate at high temperatures. The traditional lithium chloride and silica gel desiccant materials require a minimum of 180°F regeneration temperature. Where as, the new Engelhard/ICC patented zeolite desiccant material which is used in this new product line can be regenerated at very low temperatures of 120 to 140°F heat. This new feature allowed the desiccant material to regenerate using the condenser waste heat off of the air conditioning refrigerant loop.

    eled

    From 1994 to 1997, Southern Company was actively involved in the development, evaluation, and demonstration of this product.

    Advantages

    • Supplies make-up/ventilation air with higher efficiency, cost-effectively meeting increased ventilation loads per ASHRAE 62-89.
    • Can be integrated easily with existing conventional HVAC equipment; solving make-up air problems that conventional equipment can't handle.
    • Eliminates/minimizes expensive over-cooling and reheat required to dehumidify as with conventional equipment.
    • Permits independent control of humidity and temperatures control for improved comfort and control of space conditions.
    • Lower humidity levels in occupied spaces provides equivalent comfort levels at higher ambient temperatures.

    Disadvantages

    • Relatively higher unit and installation costs.
    • Units are relatively bulky. May require careful roof structure evaluation for roof-top installations.
    • Requires periodic (once a year or so) service/maintenance check up due to additional rotating parts.desiccant wheel, belt drives, evaporator pad, etc.
    • Limited manufacturers and lack of enough trained technician network

    Best applications

    Desiccants are very efficient for treating 100% make-up/ventilation air. Some of the applications include:

    1. Existing building requiring higher ventilation air either to meet ASHRAE 62-89 ventilation air requirements or increased human occupancy. Desiccant systems can be installed to treat just the make-up air portion and the outlet air from these units can be tied to return air of existing HVAC equipment. This will have the potential for minimizing/eliminating the need for major retrofitting of existing systems.
    2. In new construction, desiccant can be easily integrated with conventional HVAC designs. Desiccants can be designed to treat ventilation air portion, thereby reducing the latent load on conventional HVAC equipment. This approach will likely reduce overall energy consumption and demand. May permit the downsizing of conventional system by separating latent and sensible loads.
    3. Some the commercial applications of this type application may include schools, auditoriums, theaters, low-rise office buildings, supermarkets, restaurants, etc.
    4. Desiccant systems are also well suitable for any facility where humidity control is required or the ratio of latent to sensible load is very high. A few examples of this type of applications include:

    5. Supermarkets ---- eliminating frost build up on frozen foods, freezer case coils, and freezer case doors; reducing sweat on refrigerant cases and greatly reducing anti-sweat heater operation; and maintaining a more comfortable environment.
    6. Hospitals --- providing flexible temperature and humidity control for operating rooms; minimizing spores and bacteria, which cause microbiological growth.
    7. Ice rinks --- improving the quality of the ice by eliminating crystal formation on the skating surface, thus extending the operating season and revenue; preventing rust and mildew, and the formation of fog over the ice; extending the life of the facilities and operating equipment.
    8. Warehouse --- places requiring just the humidity control and not necessarily temperature control.

    Possible applications

  • Offices and retail stores --- helping to eliminate "sick building syndrome" by lowering relative humidity and thereby improving indoor air quality.
  • Museums, libraries, hotels, health spas, --- eliminating mold and mildew problems, along with musty odors especially in the coastal areas; extend the life of archives.
  • Technology types (resource)

    Engelhard/ICC is the only company offering these hybrid electric desiccants. They are now available in two options:

    1. 100% ventilation air systems: These units are designed to treat up to 100% of fresh air. The treated air from these units can be either supplied directly into the space or can be used as a make-up air (treating outside air portion) for conventional air conditioning units. These units are designed to remove approximately 70% latent and 30% sensible load from the outside air at rated 95°F DB and 78°F WB conditions. If the exhaust air from the space is used for regeneration, the efficiency of the unit will increase by about 10%. These units are available in the sizes ranging from 1,600 cfm to 5,000 cfm.
    2. Heat reclaim systems: These units are available in various sizes from 1,000 to 20,000 cfm and they are especially designed for supermarket application. They are designed to utilizes heat reclaimed from the store's refrigeration compressors to regenerate the desiccant materials as opposed to using air conditioner condenser heat. These units can deliver warm, dry air directly to the frozen food aisles, there by keeping relatively humidity levels near freezer aisles. When the store requires sensible cooling, cool air circulated from the conventional air conditioner will be redirected away from the frozen food section and towards the front of the store, where it is most needed.

    Contact us for a detailed list of manufacturers for this equipment.


    Warm up to reduced hot water costs and increased hot water production

    In many facilities, producing hot water is a major energy expense. The inability to produce adequate hot water when needed can severely impact operations. Fortunately, today's water heating technologies offer cost-effective solutions to meet the unique requirements of different facilities.

    Click on a topic of interest below for more information about specific water heating technologies.



    Why Electric Water Heating?

    Simplified installation and maintenance, added safety, and greater efficiency are only a few advantages.

    Electric water heating has clear advantages over fuel-fired water heating in almost all situations. Electric resistance water heating's primary disadvantage is a higher operating costs relative to gas-fired water heating under many utility rates. Even in such cases, the other advantages of electric water heating often outweigh any operating cost differences. Heat pump water heaters and other high-efficiency electrotechnologies offer operating costs lower than or similar to those of fuel-fired units under all rates.

    Safety

    • Electric water heaters are safer than fuel-fired water heaters because they avoid the hazards and problems associated with using a combustion process to heat water.
    • Combustible vapors. Fuel-fired water heaters present a potential safety hazard where flammable vapors may be present. Examples are garages, basements, and storage rooms where gasoline, paints, and cleaning fluids are stored. Flammable vapors are usually heavier than air and tend to collect near the floor. The draft effect of water heater pilot lights and burners causes the vapors to be drawn to the water heater where the pilot or burner can cause them to explode. The Consumer Product Safety Commission (CPSC) reports that during the period from 1986 through 1995, there were 4900 fire-related injuries and 341 deaths due to gas-fired water heaters and only 210 injuries and 18 deaths due to electric water heaters.
    • Allstate Insurance Company is conducting a national safety campaign directed at ignition of combustible vapors by appliances. The campaign features full-page color ads illustrating the hazard of fuel-fired water heaters where combustible vapors are present. See Harper's magazine, July 1997.
    • The CPSC data also indicates that from 1990 through 1994, an average of 11 people were killed each year by carbon monoxide produced by gas-fired water heaters.

    Indoor air quality

    Fuel-fired water heaters installed in occupied spaces create the potential for the release of combustion products into the occupied space. Damage to the flue or blockages are obvious causes. However, pressure differentials created by the operation of exhaust fans and HVAC systems or wind on the exterior of the building can also overcome the stack effect in the flue and allow flue gas to backdraft from the water heater into the occupied space.

    Simplicity and convenience

    Electric water heaters are simple. Consequently, they are the simplest and most convenient way to heat water in both residential and commercial buildings.

    Operating costs

    Under some utility rates, the cost of heating water with an electric resistance water heater is greater than the cost with a gas-fired water heater, liquid propane, and fuel oil. However, the cost difference is frequently overstated by not considering the efficiency of the water heaters. Details on factors to consider are presented in chapter 20 of the EPRI Commercial Water Heating Applications Handbook, TR100212.

    Water heating energy and demand cost is only one of the many components of the total cost of owning and operating a water heating system. Electric water heaters typically offer cost advantages over fuel-fired systems for these other cost components, including design, installation, maintenance, service life, and effect on space conditioning loads. Where the total costs of ownership and operation are considered, electric water heating often has an overall cost advantage.

    Even in situations where electric water heating is more expensive, it is frequently the preferred choice. Any cost difference is usually viewed as a small price to pay for avoiding the potential safety hazards and inconveniences associated with fuel-fired water heaters.

    Codes

    Codes and standards may impose special requirements on combustion water heating systems.

    • For example, a Wisconsin state code requires that fuel-fired water heaters within occupied spaces be installed in a two-hour rated fire enclosure. Electric water heaters have no such requirement.
    • Various codes require that fuel-fired water heaters installed in garages be elevated 18 inches above the floor to reduce the hazard associated with ignition of flammable vapors.
    • A variety of codes and standards address combustion air supplies, exhaust flues, and other features associated with the combustion process used in fuel-fired water heaters.

    Efficiency and function

    Electric resistance water heaters are more efficient than fuel-fired units.

    Table 1 lists minimum energy factors set by the National Appliance Energy Conservation Act, NAECA, for various system types and tank volumes and maximum values published in the December 1995 edition of the software version of the GAMA directory. The maximum energy factor listed for fuel-fired units with power burners is 0.86. For units with atmospheric burners, the maximum energy factor is 0.64. Electric water heaters have energy factors as high as 0.95.

    Table 1

    NAECA-Required Minimum Energy Factor and Best Available Energy Factors

    Nominal
    Volume (gal)
    Electric
    Resistance
    Gas and LP Oil
    Min Max Min Max Min Max
    20 0.904 0.94 0.582 0.61 0.552 na
    30 0.890 0.95 0.563 0.63 0.533 0.62
    40 0.877 0.95 0.544 0.70a 0.514 na
    50 0.864 0.95 0.525 0.86b 0.495 0.55
    65 0.844 0.92 0.497 0.54 0.467 na
    80 0.824 0.94 0.468 na 0.428 na
    100 0.798 0.94 0.430 0.48 0.400 na
    120 0.772 0.86 0.392 na 0.362 na

    a. Discontinued model; highest current model is 0.66.

    b. Typical values are much lower.

    Source: Minimum energy factors are from NAECA; maximum values are from GAMA Consumers' Directory of Certified Efficiency Ratings, October 1997

    Lower standby loss

    Because they are much better insulated, electric resistance water heaters have less standby losses than fuel-fired units. Fuel-fired storage water heaters lose substantial amounts of heat through their flues and the un-insulated tank bottom. Typical fuel-fired water heaters lose about 3.5% of their stored heat per hour. Typical electric water heaters lose only about 1% per hour. Where hot water usage is low, the cost of operating an electric water heater can be lower than the cost for a natural gas unit.

    Applications

    Availability - Electric service is available almost everywhere a water heating system would be installed. Natural gas is not available in many areas, particularly in rural locations. While all buildings have electric service, natural gas service is optional. If not provided for other loads, installation costs and basic service costs must be recognized.

    Point-of-use service - Electric water heaters are ideal for point-of-use water heating systems, where the water heaters are installed at or near the locations where hot water is required. Fuel-fired systems must be located where combustion air is available and flues can be installed. Locating the water heater closer to the hot water usage points reduces piping costs and piping heat loss and reduces the wait for hot water at the fixtures. The need for recirculation loops and pumps is also reduced.

    Electric water heaters are readily incorporated as supplemental units with solar water heaters, heat pump water heaters, and refrigeration heat reclaim water heaters.

    Electric water heaters are convenient for use as booster heaters where higher-temperature water is required for special functions, such as dishwashing.

    Design and installation

    Electric water heaters are readily incorporated into building and mechanical system designs. The combustion process and flues associated with fuel-fired systems present complications.

    • Location - Electric water heaters can be located almost anywhere within a building without the need for combustion air and flues. They can be placed under counters and in cabinets, avoiding the use of expensive floor space. With building costs of $200/sq ft or more in commercial buildings, a small amount of extra space can be quite expensive.
    • Clearance around combustible materials - Fuel-fired water heaters require additional clearance from combustible materials.
    • Gas piping - Gas piping must be routed to the water heater.
    • Flues - Flues must be routed to the exterior of the building. Unless more expensive power-driven flues are used, the flue must be sloped upward to assure good draft. Flues are particularly difficult for water heaters located on lower floors and interior spaces away from the building perimeter.
    • Combustion air - Fuel-fired water heaters require air for combustion. Air must be able to flow from the outdoors into the building and into the space where the water heater is installed. A substantial ventilation area is required.
    • Interaction of combustion air and flue with other air moving systems - The interactions between a fuel-fired water heater's combustion air system and flue and other building systems such as exhaust fans and HVAC units must be considered. Natural-draft combustion air/flue systems are particularly subject to poor performance with improper air balance in a building. When other air-moving systems create a low pressure inside the building, flue gasses may be drawn into the building interior rather than flowing through the flue to the outdoors. For example, if a restaurant exhaust hood is provides excessive airflow or if a makeup air vent is blocked, the resulting low interior pressure can cause combustion gasses to flow downward through the water heater flue so quickly that the unit's pilot light can be extinguished. This results in air-quality problems, safety hazards, and an interruption in hot water service.
    • Effect of draft on infiltration loads - For fuel-fired water heaters inside conditioned spaces, building heating and cooling loads are increased by the flow of outdoor air into the interior for combustion and flue gas removal.
    • Appearance of flue - Unless located in a hidden or unimportant area, a water heater flue on the building exterior can be unsightly. Architects and designers seldom consider them until after construction is complete.

    Maintenance

    Fuel-fired water heaters require more maintenance than electric units because of their greater complexity and the combustion process. Burners and flues are subject to corrosion and mechanical damage. Larger systems require periodic checks and adjustment of the burners to avoid declines in efficiency. Roof penetrations for flues present potential leak points.

    System life and warranties

    Electric water heaters usually have longer service lives than fuel-fired units. Table 2 provides typical life spans.

    Table 2

    Typical Life Spans for Residential Water Heaters

    Type Life
      Low Average High
    Gas 8 11 14
    Electric 10 14 18

    Source: Appliance magazine, September 1995. Cited in Market Disposition of High-Efficiency Water Heating Equipment, Arthur D. Little, Inc. for the U.S. Department of Energy, NTIS PB97-145379, November 1996.

    Fuel-fired water heaters present particular problems in environments where potentially corrosive airborne chemicals are present. Laundries and beauty parlors are examples. Detergent particles and chemicals in the air react in the water heater's combustion chamber to form corrosive products that can cause rapid failure of the flue and tank bottom. Some water heater manufacturers specifically exclude such applications from their warranties.

    Miscellaneous

    All-electric rates - The use of electric water heating makes it possible for customers to take advantage of all-electric rates and other utility incentives.


    Water Heating Performance Measurements

    Learn several ways to measure and compare the performance of water heating systems.

    Water heating capacity

    Water heating capacity is described in BTUH or by recovery rate in gallons per hour. Recovery rate figures are usually based on an 80°F temperature rise; various temperature changes are used. To convert recovery rate in gallons per hour to capacity in BTUH, use:

    equation1

    HPWH water heating capacity is sometimes described in tons. This is inappropriate and confusing, because "ton" is a measure of cooling capacity. This publication uses BTUH for describing water heating capacity.

    Energy factor

    Energy factor is a delivered efficiency figure defined by the US DOE test procedure "Uniform Test Method for Measuring the Energy Consumption of Water Heaters." It is calculated from data taken for a specific pattern of hot water use during a 24-hour hot water usage test. The higher the energy factor, the lower the energy consumption. The test used 64.3 gallons of hot water per day at nominal temperatures of 135¼F for hot water, 58¼F incoming cold water, and 67.5¼F air temperature.

    Details of the test procedure are available in the Federal Register. A summary is presented in Electric Water Heating News, volume 4, number 2, Summer 1991.

    Energy factor is not the same as water heating efficiency; it is defined only for the specific set of conditions in the test procedure. The actual efficiency of a water heater varies greatly with the amount of hot water used, inlet water temperature, hot water delivery temperature, and other operating conditions. EPRI's WATSMPL software provides a convenient means of calculating water heating efficiency at any set of conditions, using energy factor as an input.

    For commercially available storage water heaters, energy factor is generally higher for units with smaller tanks, however it varies substantially depending on design and construction details. For typical electric storage water heaters, energy factor ranges from 0.77 to 0.95, with a typical value of about 0.86. For gas storage water heaters, energy factor ranges from 0.43 to 0.86, with 0.54 a typical value. For gas units, recovery efficiency ranges from 75 to 94%. Electric units have recovery efficiencies of essentially 100%.

    Table 1 lists minimum energy factors set by NAECA for various system types and tank volumes. Also included are the maximum values in each category for all models listed in the October 1997 edition of the GAMA directory.

    Heat pump water heaters are much more efficient than both gas-fired and electric resistance water heaters. Values of EF for various residential HPWH models range from 2.0 to 2.5. Because energy factors defined under the US DOE test procedure consider tank heat loss, they are substantially lower than energy factors defined by the 1983 GAMA procedure, which did not consider tank loss.

    Table 1

    NAECA-Required Minimum Energy Factor and Best Available Energy Factors

    Nominal
    Volume (gal)
    Electric
    Resistance
    Gas and LP Oil
    Min Max Min Max Min Max
    20 0.904 0.94 0.582 0.61 0.552 na
    30 0.890 0.95 0.563 0.63 0.533 0.62
    40 0.877 0.95 0.544 0.70a 0.514 na
    50 0.864 0.95 0.525 0.86b 0.495 0.55
    65 0.844 0.92 0.497 0.54 0.467 na
    80 0.824 0.94 0.468 na 0.428 na
    100 0.798 0.94 0.430 0.48 0.400 na
    120 0.772 0.86 0.392 na 0.362 na

    a. Discontinued model; highest current model is 0.66.

    b. Typical values are much lower.

    Source: Minimum energy factors are from NAECA [9]; maximum values are from GAMA Consumers' Directory of Certified Efficiency Ratings, October 1997

    First hour rating

    First hour rating was created by US DOE for use by the Federal Trade Commission in categorizing water heaters. First hour rating as now defined is flawed and should not be used for sizing and selecting water heaters. Recent tests show that one hour is too long a period for sizing water heaters. Hot water delivery over a 15- to 30-minute period is usually the determinant for water heater sizing.

    The current US DOE first hour rating was flawed and is not in use. A revised test procedure and rating are being developed but have not yet been released.

    The first hour rating commonly used and reported in the GAMA directory is quite different. It is determined by heating the storage tank to 135°F and drawing water at three gallons per minute with 58°F inlet water until the outlet water temperature drops to 110°F. The HPWH and/or elements, if any, are allowed to operate. The amount of hot water that the water heater could theoretically heat to 135°F during the remainder of the one-hour period is added to the measured quantity of delivered hot water. First hour rating is expressed in gallons.

    The first hour rating definition and test procedure as they are now defined have limited applicability and practical use. The rating gives artificially higher ratings to fuel-fired units relative to electric systems than what is appropriate. For more information refer to "Water Heater First-Hour Rating vs. In-Field Performance," AT-96-18-4, ASHRAE Transactions, Vol. 102, Part 1, Atlanta, GA, 1996, Hiller, Carl C., P.E., Ph.D. [27] and "New Hot Water Consumption Analysis and Water Heating System Sizing Methodology," SF-98-31-3, ASHRAE Transactions 1997, Hiller, Carl C., P.E., Ph.D.

    Hourly percent tank heat loss

    The GAMA directory once included ratings for water heater standby loss. Heat loss was expressed as a percentage of total stored energy lost per hour. Although no longer used by GAMA, the figure remains a convenient means of expressing tank heat loss. EPRI's WATSMPL software can be used to calculate hourly tank loss for various operating conditions using energy factor ratings. Hourly percent tank heat loss is used as an input value for EPRI's HOTCALC software.

    Recovery rate and recovery efficiency

    Recovery rate is the rate at which a water heater can heat water through a specified temperature difference. Recovery efficiency is the efficiency of the water heater during continuous operation for the heating process. Recovery rate and recovery efficiency were formerly reported in the GAMA directory for all water heaters. Recovery efficiency is still reported for gas and oil water heaters, but not for HPWHs or electric resistance units.

    GAMA

    The Gas Appliance Manufacturers Association (GAMA) tests and certifies electric, gas, oil, and heat pump water heater performance using the U.S. Department of Energy test procedure for water heaters. The test procedure addresses all water heaters covered by the National Appliance Energy Conservation Act (NAECA). Models meeting the following criteria are included.

    • Electric resistance storage water heaters - 20 to 120 gallons, <12 kW input
    • HPWH - current rating <24 A at no more than 250 V
    • Gas storage water heaters - 20 to 100 gallons, <75,000 BTUH input
    • Oil storage water heaters - < 50 gallons, <105,000 BTUH input
    • Gas instantaneous water heaters - input ratings <50,000 BTUH and <200,000 BTUH and <180° F delivery temperature
    • GAMA publishes the Consumers' Directory of Certified Efficiency Ratings for Residential Heating and Water Heating Equipment which includes first hour rating, energy factor, and storage volume.

    Air conditioning capacity

    Total cooling capacity and sensible and latent capacity are stated in BTUH or nominal tons (one ton = 12,000 BTUH). These measures are similar to those used for conventional air conditioners. Latent capacity may also be expressed in pints of water removed per hour, similar to dehumidifier ratings.

    equation2

    Latent and sensible capacity are also described by latent fraction or sensible fraction. The fractions indicate what portion of the total capacity is provided by latent cooling and sensible cooling, respectively. The sum of the latent fraction and sensible fraction is one.

    Air conditioning capacity and efficiency vary greatly with temperature and humidity. When comparing alternative units, use information based on consistent conditions. Also, for design and analysis, use performance figures appropriate to the conditions at which the heat pump will be applied. For example, a HPWH applied in a 90¼F, 80% relative humidity space will be substantially more efficient and have much greater capacity than indicated by the figures for the standard ARI rating conditions.


    Water Heating Electrotechnologies

    Quickly survey a wide range of electric water heating solutions that are available today.

    Quick recovery electric resistance storage water heater

    The most common type of electric water heater used in the United States. There are normally two 4500-watt elements, one upper and one lower in a tank holding 50 to 66 gallons. The tank is usually made of steel lined with glass for corrosion protection.

    Base-loaded electric resistance storage water heater

    A storage water heater with one or two 500- to 3000-watt elements and an 80- to 120-gallon tank. The greater storage volume and lower wattage elements levels the electrical load, shifting demand from utility peak load hours to off-peak hours.

    Off-peak electric resistance storage water heater

    A storage water heater unit in which the elements are controlled by a timer or remote control device such as a radio or power line carrier signal that allows operation only during utility off-peak hours. There are usually has one or two elements with power levels from 500 to 4500 watts and tank volume is usually 80 to 120 gallons. The elements are typically prevented from operating for 2 to 12 hours. Multiple tanks may be used.

    Interruptible electric resistance storage water heater

    A storage water heater in which operation of the elements is remotely controlled, typically by radio or power line carrier signal, to disable element operation during utility peak loads. Typical units use 4500-watt elements and a 50- to 80-gallon tank. Interruption periods are typically less than 4 hours.

    Point-of-use electric resistance water heater

    A storage water heater installed near the point where hot water is used. The location reduces the time required to obtain hot water and avoids the use of a pumped recirculation loop and the associated high heat loss. Typical residential units use a 1- to 20-gallon tank while commercial applications usually call for larger units.

    Instantaneous electric resistance water heater

    Instantaneous water heaters have little or no storage capacity and heat water as it is needed with heating elements activated by a flow switch. Residential installations commonly have 6000- to 9000-watt heating elements capable of heating about one gallon per minute from 60 to 110¼ F. Commercial installations are available with much higher power ratings and are often custom built for the application.

    Electric resistance pipe wrap

    Pipe wrap heaters features a self-temperature-regulating wire which is wrapped around pipes to offset heat loss so hot water is immediately available at the point of use. Electric pipe wrap is also used for to provide freeze protection for piping.

    The plastic tank electric resistance water heater is similar to other types of electric resistance units except the tanks are made of nonmetallic materials. Advantages include less susceptibility to corrosion and lighter weight, which makes shipping and installation easier.

    The tanks of concrete-lined electric resistance water heaters are made of steel lined with concrete. These reportedly are less susceptible to corrosion than are glass-lined steel tanks, but they are substantially heavier.

    A newcomer to the U.S. market, the plastic-lined electric resistance unit has a plastic-lined steel tank, which weighs approximately the same as a glass-lined tank but is reported to be less susceptible to corrosion.

    Tanks for unpressurized electric resistance water heaters differ from others described here in that water is stored at atmospheric pressure instead of city water pressure. A special pump utilizes city cold water pressure to pump hot water out of the tank and send it to the point of use. Advantages include availability of lower cost tanks in sizes above 120 gallons, light weight, ruggedness for shipping and handling, and ease of installation. This type of tank is now under development and should be available in the United States soon.

    A booster heater is installed somewhere between one point of use and the main water heater and is used to raise water temperature to the final desired level. Boosters allow the main building water heater thermostat to be set at the lowest temperature appropriate for the majority of uses, rather than at the highest temperature needed for single point of use. Tank or tankless (instantaneous) units can be installed, or the boosters can be built into end-use devices such as dishwashers.

    Waste heat recovery

    A waste heat recovery (desuperheater) water heater is installed in a vapor compression system between the compressor and the condenser. It utilizes hot refrigerant vapor exiting the compressor to heat water, but does nor remove enough heat from the refrigerant to cause it to condense. This makes it possible to retrofit existing vapor compression systems with desuperheaters without redesigning the refrigerant circuit. This electrotechnology is attractive because water heating energy is essentially provided free. heated water is circulated into a conventional water heater tank for storage. A backup water heating energy source is necessary to provide hot water when the vapor compression device (e.g., air conditioner, heat pump, or refrigerator) is not in use.

    The waste heat recovery (full-condensing) multifunction technology is similar to that of desuperheater water heaters, but the system is designed to fully condense refrigerant, allowing the capture of more waste heat for water heating. More importantly, it allows stand alone water heating capability. For example, when incorporated in an air conditioner or heat pump, the unit has multiple operating modes: space heating only, space cooling only, space cooling plus water heating, and water heating only. On an annual basis, because of their stand-alone water heating capability, such systems provide considerably more hot water than do desuperheaters.

    Heat pump water heaters (HPWHs)

    A heat pump water heater (HPWH) without a tank is an air-source vapor compression heat pump that is specifically designed to heat domestic water and to be connected to a conventional water heater tank. Such units can be retrofit to existing water heaters. They are highly efficient--annual coefficients of performance range from 2.0 to 3.0, which means they consume one-half to one-third as much electricity as electric resistance units.

    A HPWH with a water storage tank is somewhat more efficient than a tankless unit. It must either replace or be connected in series with an existing water heater. Annual coefficients of performance range from 3.0 to 4.0.

    A HPWH with a single ducting for airflow manipulation (tank or tankless) includes a ducting connection and a fan capable of forcing air through the ducting. Such units are useful for moving cool, dehumidified air from the heat pump into areas where cooling is desired or away from areas where cooling is not desired. Alternatively, the ducting can supply the heat pump with higher-temperature air to achieve better water heating performance or remove heat from unconditioned areas such as attics. If ducting is routed to the outdoors, the units can assist in building ventilation.

    A HPWH with double ducting for airflow is similar to a single-ducted unit but has two sets of ducting connections and two fans for forcing air through ducting. It can simultaneously heat water and achieve air-to-air heat exchange for ventilation in tightly constructed buildings.

    A swimming pool HPWH is tankless except that a swimming pool serves as a tank. Unlike units designed to heat potable water, these water heaters are constructed of materials capable of withstanding exposure to typical swimming pool chemicals, since most swimming pools are heated to less than 90¼, the equipment is optimized for better low-temperature performance.

    A spa HPWH is similar to a swimming pool HPWH but is designed to heat water to higher temperatures, typically 110 to 120¼F.

    A water-to-water HPWH is a vapor compression water heating device that utilizes water instead of air as the heat source. This type of system is found mostly in commercial applications for utilizing waste heat in cooling-tower water circuits. Variations exist for use with other types of water loops, such as ground-coupled heat exchangers. Both residential and commercial equipment is available.


    Electric Resistance Storage Water Heaters

    These extremely common units come in a range of storage capacities and are known for their quick recovery times.

    Storage water heaters are the most common type of water heater used in both residential and commercial applications. Storage water heaters incorporate heating elements or a burner and tank into a single unit. Electric units are typically available in one- to 120-gallon capacity with input ratings of 1 kW to 54 kW. Most smaller units, including almost all units applied in residences, are dual-element units with an upper heating element and a lower element controlled to prevent simultaneous operation. A typical electric resistance storage water heater is shown here:

    estoragewh

    Larger commercial water heaters may have several banks of elements that are allowed to operate simultaneously. Virtually all commercial electric units are 208 V or higher, either single or three phase. With 120-V service, maximum input capacity is limited to 1.9 kW or less.

    The most common commercial gas storage water heaters vary in size from 20 to 100 gallons. Input ratings range from 30 to 600 kBTUH.

    In almost all code jurisdictions, storage water heaters or hot water tanks must be ASME labeled if their capacity is greater than 120 gallons or if the rated input is 200 kBTUH or more. Higher-cost ASME-rated water heaters are available in capacities up to 5000 gallons and input ratings of 2000 kW and 750 kBTUH. As an alternative to high-cost ASME-rated tanks, several smaller, non-ASME-rated units may be used to provide equivalent capacity.

    In comparing gas and electric water heaters, it is not appropriate to simply compare input ratings. Electric storage water heaters are inherently more efficient than gas units. While typical gas water heaters are limited by a combustion and heat transfer efficiency of about 78 to 80%, electric water heater elements are immersed in the tank, so that the conversion efficiency is 100%. Typical gas water heater tanks also have greater heat loss because of the uninsulated flue through the center of the tank and the uninsulated tank bottom. Thus, for similar input ratings, an electric water heater delivers significantly more heat input capacity.

    Most electric storage water heaters are controlled by surface-mounted adjustable thermostats, although larger units may use immersion thermostats. In electric units, the upper and lower elements are controlled by separate thermostats which are adjustable from about 110 to 180°F. Fuel-fired water heaters have a single immersion thermostat. On all water heaters, control resolution is coarse and accuracy is limited.

    Applications

    • All applications where simplicity, convenience, and safety are primary considerations.
    • Where installation of flues and provision of combustion air for fuel-fired systems would be inconvenient, unattractive, difficult or impossible or where potentially dangerous backdrafting may occur due to indoor/outdoor pressure differentials.
    • Where hot water usage is low, the low standby loss of electric water heaters can make them less expensive than natural gas systems.
    • Point-of-use applications.

    Possible applications

    Most residential and commercial facilities are good candidates for electric resistance storage water heaters.

    Efficiency

    Electric storage water heaters are inherently more efficient than gas units. While typical gas water heaters are limited by a combustion and heat transfer efficiency of about 77% or less (higher for pulse-combustion and condensing water heaters), electric water heaters have their elements immersed in the tank, so that the conversion efficiency is close to100%. Gas water heater tanks also have greater heat loss because of the open flue through the center of the tank.

    Because they are well-insulted, heat loss from the tank is low and air temperature has little effect on the operation and performance of electric water heaters.

    Contact us for a detailed list of manufacturers for this equipment.

    Other information

    Minimum efficiency requirements for storage water heaters sold in the United States are specified by the National Appliance Energy Conservation Act or NAECA. A number of other codes and standards also apply. Storage water heaters larger than 120 gallons or with input ratings of 200 kBtuh (58.6 kW) or more must comply with ASME pressure vessel standards, which substantially increases their cost.

    Energy factor

    The National Appliance Energy Act of 1987 and the 1988 amendments established minimum energy factors for electric, gas-fired, and oil-fired water heaters manufactured after January 1, 1990. Minimum figures were revised for equipment manufactured after April 15, 1991; see table1. The standards apply to storage water heaters having capacities equal to or smaller than the following:

    • Gas: 75 kBtuh input
    • Oil: 105 kBtuh input
    • Electric: 12 kW input

    Table 1

    NAECA Water Heater Energy Factor Standards

    Product Class Energy Factor
    Gas water heater
    0.62 - (0.0019 x rated storage volume in gallons)
    Oil water heater 0.59 - (0.0019 x rated storage volume in gallons)
    Electric water heater 0.93 - (0.00132 x rated storage volume in gallons)

    Source: Federal Register: Energy Conservation Program for Consumer Products, October 17, 1990, [11].

    For commercially available storage water heaters, energy factor is generally higher for units with smaller tanks, however it varies substantially depending on design and construction details. For typical electric storage water heaters, energy factor ranges from 0.77 to 0.95, with a typical value of about 0.86. For gas storage water heaters, energy factor ranges from 0.43 to 0.86, with 0.54 a typical value; recovery efficiency ranges from 75 to 94%. Table 2 lists minimum energy factors set by NAECA for various system types and tank volumes. Also included are the maximum values in each category for all models listed in the October 1997 edition of the GAMA directory.

    Table 2

    NAECA-Required Minimum Energy Factor and Best Available Energy Factors

    Nominal
    Volume (gal)
    Electric
    Resistance
    Gas and LP Oil
    Min Max Min Max Min Max
    20 0.904 0.94 0.582 0.61 0.552 na
    30 0.890 0.95 0.563 0.63 0.533 0.62
    40 0.877 0.95 0.544 0.70a 0.514 na
    50 0.864 0.95 0.525 0.86b 0.495 0.55
    65 0.844 0.92 0.497 0.54 0.467 na
    80 0.824 0.94 0.468 na 0.428 na
    100 0.798 0.94 0.430 0.48 0.400 na
    120 0.772 0.86 0.392 na 0.362 na

    a. Discontinued model; highest current model is 0.66.

    b. Typical values are much lower.

    Source: Minimum energy factors are from NAECA; maximum values are from GAMA Consumers' Directory of Certified Efficiency Ratings, October 1997


    Instantaneous Electric Resistance Water Heaters

    Installed at the points where hot water is needed, these small units produce hot water on demand (with little or no hot water storage).

    Instantaneous electric water heaters use high-input heating elements to produce hot water on demand. They have little or no storage capacity. Their primary advantages are their small size, the absence of standby loss, and their suitability for installation at the points of hot water use to serve specific individual loads. Small units are often installed to serve individual lavatories or showers. Disadvantages include higher first cost, the possibility of increased electrical demand, and limited hot water delivery capacity.

    Most instantaneous water heaters activate the heating elements with a flow switch and rely on a thermostat to regulate the supply water temperature. Because they heat water continuously and do not use stored hot water to meet loads, instantaneous water heaters can supply an essentially constant stream of hot water. However, delivery rates are somewhat limited. Typical small units provide hot water at rates up to about 2.5 gallons per minute.

    Because fuel-fired instantaneous water heaters have higher thermal capacitance, their efficiency suffers substantially when the units cycle frequently.

    Instantaneous water heaters heat water on demand rather than storing heated water in a tank. The heating elements in an instantaneous water heater are controlled by a flow switch and thermostat. The flow switch allows the elements to operate only when water is flowing through the heater. The thermostat limits the maximum output temperature to the desired limit. When a hot water tap is opened, flow begins and the heating elements are energized to heat the water. The heat input rate is usually constant; at lower flow rates, the elements cycle on and off to deliver the desired temperature.

    Applications

    • In general, low-flow uses of hot water in isolated or remote locations in a building.
    • Distributed lavatories and sinks in shopping malls, offices, public facilities, schools, service stations, schools, and other building types.
    • Point-of-use applications in commercial buildings for low-flow hot water uses, especially restrooms.

    Possible applications

    • Instantaneous water heaters may also be installed at the points of use as in-line heaters on the hot water line of a conventional water heater to avoid a long wait for hot water to arrive from the central water heater when a tap is opened.

    Efficiency

    The volume of hot water delivered by an instantaneous water heater is limited by the electrical input capacity of the heater and the circuit serving the heater and the incoming cold water temperature. Useful capacity declines somewhat during winter when the incoming water temperature is low. The following table illustrates the maximum temperature increase provided by typical instantaneous water heaters. Cold water inlet temperatures are below 35°F during winter in many locations, indicating that such heaters are inadequate to meet many hot water loads.

    Typical
    Voltage
    Input
    (kW)
    Temperature Increase (°F)
        0.5
    gpm
    0.75
    gpm
    1.0
    gpm
    1.5
    gpm
    2.0
    gpm
    110 3 41 27 20 14 10
    208/220 4.5 61 41 31 20 15
    208/220 7 95 64 48 32 24
    240 9.5 123 82 61 41 31

    Point-of-Use Water Heaters

    Installed at or near the point where hot water is needed, these storage type units reduce piping costs, lower heat loss, and shorten waits for hot water.

    Where individual hot water loads are isolated, a point-of-use water heater may be used instead of a central source system. Point-of-use systems avoid the long piping runs and the related cost and heat loss associated with central hot water systems and distributed points of use. Point-of-use water heater systems consist of multiple instantaneous water heaters and small-volume storage water heaters located at or near the location where hot water is needed.

    Point-of-use water heater applications provide hot water at or near the location where it is needed. They operate without the heat loss of central hot water systems with long piping runs and recirculation loops. The short distance between the water heater and the point of use means that hot water is available almost immediately, without wasting water and waiting for heated water to flow from the central system.

    Applications

    • In general, low-volume uses of hot water in isolated or remote locations in a building.
    • For hot water loads which require prompt delivery of hot water to the fixtures.
    • In buildings where central water heating system would be very expensive or difficult to install.
    • In place of recirculation loops.

    Possible applications

    • Remote bathrooms.
    • Hotels and motels.

    Efficiency

    Storage water heaters

    Electric storage water heaters are inherently more efficient than gas units. While typical gas water heaters are limited by a combustion and heat transfer efficiency of about 77% or less (higher for pulse-combustion and condensing water heaters), electric water heaters have their elements immersed in the tank, so that the conversion efficiency is close to100%. Gas water heater tanks also have greater heat loss because of the open flue through the center of the tank.

    Because they are well-insulted, heat loss from the tank is low and air temperature has little effect on the operation and performance of electric water heaters.

    Instantaneous water heaters

    The volume of hot water delivered by an instantaneous water heater is limited by the electrical input capacity of the heater and the circuit serving the heater and the incoming cold water temperature. Useful capacity declines somewhat during winter when the incoming water temperature is low. The following table illustrates the maximum temperature increase provided by typical instantaneous water heaters. Cold water inlet temperatures are below 35°F during winter in many locations, indicating that such heaters are inadequate to meet many hot water loads.

    Typical
    Voltage
    Input
    (kW)
    Temperature Increase (°F)
        0.5
    gpm
    0.75
    gpm
    1.0
    gpm
    1.5
    gpm
    2.0
    gpm
    110 3 41 27 20 14 10
    208/220 4.5 61 41 31 20 15
    208/220 7 95 64 48 32 24
    240 9.5 123 82 61 41 31

    Air-Source Heat Pump Water Heaters

    Remove hot, humid air from laundries or other high heat areas, cooling those areas while essentially providing free water heating energy.

    The basic operation of a heat pump water heater (HPWH) can be readily understood by examining it as a black box, without regard to the inner workings. Using this simplified approach, Figure 1 illustrates the three energy flows involved with a typical HPWH. The HPWH consumes electric energy and it removes heat from the heat source, producing a cooling effect. The energy gained is then delivered by the HPWH as heating output. For an air-source HPWH, the heat source is usually warm, humid interior air. Water-source heat pumps usually rely on a chilled water loop or a cooling tower loop as a heat source.

    HPWHs use a small amount of electricity to upgrade the temperature of a large amount of heat and deliver it to meet a thermal load. The water heating efficiency of a heat pump water heater is always greater than 100%, and usually substantially greater. In addition to the water heating output, HPWHs often provide a useful cooling and dehumidification effect with no additional energy input.

    heatpumpheatinset1

    Heat pump water heater energy flow

    The electric energy input results in two useful effects: cooling and heating. The heating output (electrical input + heat removed from the heat source) is applied toward a water heating load. The cooling output is often used to cool and dehumidify the interior of a building. Since HPWHs have efficiencies greater than 100%, water heating efficiency for a HPWH is described by the coefficient of performance or COP, instead of using the term "efficiency." The water heating COP is the ratio of the useful water heating output to the electric energy input.

    Under typical conditions, an air-source HPWH delivers about 10,000 BTUH of water heating for every kilowatt of electric power it uses. It typically achieves a maximum temperature of about 130-150°F depending on the refrigerant used. While heating water, the HPWH also provides a cooling effect of about 6700 BTUH per kilowatt. Like a conventional air conditioner, typically about 75% of the cooling output is sensible cooling and 25% is latent cooling or dehumidification at standard rating conditions.

    The fundamental principles of operation for a HPWH are the same as those of a room air conditioner, a refrigerator, or an air-to-air heat pump. The basic functional components of a heat pump water heater are the evaporator, compressor, condenser, and expansion device, as shown in Figure 2.

    hpwh1_2

    Heat pump schematic

    Heat is transferred by the flow of refrigerant (currently HCFC-22 or HFC-134a), taking advantage of the large amount of heat absorbed and released when the refrigerant evaporates and condenses. The flow of refrigerant is caused by the pressure differential created by the compressor. The compressor and condenser operate at higher pressure; that portion of the refrigeration system is called the high side. The portion containing the evaporator and the expansion device is called the low side. The compressor pulls refrigerant from the evaporator on the low side and discharges it to the condenser on the high side, much like a pump lifting water uphill. The expansion device resists the flow of refrigerant back to the low side, maintaining the pressure differential.

    The refrigeration cycle

    The refrigeration cycle is best understood by following a portion of the refrigerant around the cycle. The processes that occur in the major components are described in the following paragraphs.

    Compression

    Drawn by the compressor, refrigerant gas (vapor) leaves the evaporator at low pressure and low temperature and flows through the suction line to the compressor. As the compressor compresses the vapor to a higher pressure, its temperature rises (in the same manner as a bicycle pump becomes warm when pumping up a tire).

    Refrigerant leaves the compressor as a high-temperature gas at high pressure.

    Condensation

    The compressor pushes hot, high-pressure refrigerant through the discharge line to the condenser. The condenser is simply a heat exchanger that removes heat from the hot gas and releases it to a heat sink (for HPWHs, the water being heated). The removal of heat from the hot gas causes it to condense to a liquid.

    Refrigerant leaves the condenser as an intermediate-temperature liquid at high pressure.

    Pressure drop and expansion

    Liquid refrigerant flows from the condenser through the liquid line to the expansion device. By acting as a flow restrictor, the expansion device maintains high pressure on the condenser side and low pressure on the evaporator side. In larger commercial heat pump water heaters, the expansion device is an expansion valve. In smaller systems, it may be a capillary tube.

    As the liquid moves through the expansion device, its pressure is suddenly lowered. The pressure drop causes some of the liquid refrigerant to flash (evaporate very quickly) into vapor. The evaporation of a portion of the liquid cools the remaining liquid, in the same way evaporation cools your skin when you step out of the shower.

    Refrigerant leaves the expansion device as a low-temperature mixture of gas and liquid at low pressure.

    Evaporation

    The cold, low-pressure mixture of liquid and gas refrigerant then flows to the evaporator. The evaporator is another heat exchanger that allows heat to move from a heat source (the air inside a building for most air-source HPWHs) to the refrigerant. As the liquid refrigerant evaporates to a gas, the evaporator removes heat from the heat source. The evaporator in an air-source HPWH provides a cooling and dehumidification effect for the building interior as the evaporator removes heat from the air. Dehumidification takes place only when the evaporator surface temperature is below the air's dewpoint temperature, allowing moisture to condense.

    Refrigerant leaves the evaporator as a low-temperature gas at low pressure, completing the cycle. The cycle is continuous while the machine is in operation, with refrigerant continuously moving through each part of the system.

    Most vapor compression refrigeration devices are dedicated to achieving only a single effect. Refrigerators and air conditioners remove heat from food storage compartments and building interiors. In winter, space conditioning heat pumps deliver heat to the interior of a building. The energy flow on the other side of the cycle is incidental. Heat pump water heaters achieve higher efficiency by accomplishing two useful functions simultaneously. They cool the building interior while heating water. See Figure 3. Unlike conventional devices, there is no "waste" of output.

    hpwh2

    Coefficient of performance: the multiplier effect

    Coefficient of Performance (COP) is simply a measure of efficiency or the amount of useful output achieved for a given input. For example, an air-to-air heat pump might operate at a COP of three under favorable heating season conditions. This means that it delivers three units of heat to the building interior for each unit of energy consumed as electric energy.

    HPWHs and other refrigeration devices are able to move more energy than they consume by taking advantage of the large amount of heat absorbed and released when the refrigerant evaporates and condenses. Air conditioners, refrigerators, freezers, and air-to-air heat pumps all operate similarly, with COPs normally about 1.7 to 3.2. However, they obtain a useful benefit only on one end of the heat transfer process.

    In the example of Figure 4, the refrigeration device provides two units of cooling and consumes one unit of electric energy. The COP for the cooling process is 2.0. If the device is used for heating, the COP is 3.0.

    hpwh3

    COP of conventional refrigeration device

    Figure 5 illustrates the heat and energy flows typical of a commercial heat pump water heater. Notice how the HPWH uses the electric energy input to create two useful energy flows. It achieves the same cooling effect as in the previous example while also making use of the heating effect. An energy "investment" in one unit of electric energy yields energy "dividends" of two units of cooling and three units of heating.

    hpwh4

    COP of HPWH system

    Using more specific figures, a typical HPWH operating at normal conditions delivers about 10,000 BTUH of water heating for every kilowatt of electric power input (the equivalent of 3413 BTUH). About 15 gallons of water can be heated per hour through a temperature change of 80°F. The coefficient of performance for water heating is 10,000 / 3413 or about 2.9. In addition, about 6600 BTUH of cooling and dehumidification capacity is delivered for the same one-kilowatt input. The total water heating output is approximately equal to the sum of the electric power input and the cooling capacity.

    Rule of thumb: For each kilowatt of electric power input, a typical HPWH operating at normal conditions delivers about 10,000 BTUH of water heating and 6600 BTUH of cooling and dehumidification.

    These rule-of-thumb values agree closely with the actual specifications for most specific HPWHs applied in typical conditions. As an example, one commercially available HPWH model uses five thousand Watts (17,100 BTUH) of electric power to deliver 50,000 BTUH of water heating and 31,500 BTUH of cooling. A total of 81,500 BTUH of useful heat flow is provided.

    Applications

    Heat pumps are not a universal solution to water heating and space cooling energy cost reduction. In the right application, they perform exceptionally well; in the wrong application, the results may be disappointing. Potential applications should be evaluated to select sites that offer the best performance and high run time to achieve good return on investment. Poor or marginal applications will only lead to unfulfilled expectations and dissatisfied customers. After a good application has been selected, the appropriate HPWH system must be selected to address the customer's specific priorities for water heating cost savings and space cooling.

    Best applications

    High HPWH run time is the key to successful heat pump water heater applications. High run time is achieved by applying a properly sized HPWH in facilities with significant water heating loads.

    • Where there are large hot water consumption.
    • Laundries and restaurants are common applications for HPWHs.
    • Any facility which uses hot water and has a simultaneous need for additional space cooling and dehumidification.
    • Where natural gas, liquid propane gas, oil, or electric resistance heat are expensive.
    • Facilities where overheating and high humidity are serious problems.
    • Residences with a source of waste heat, including basements, attics, and laundry rooms.

    Possible applications

    HPWHs can sometimes be justified in applications where the cooling output is not valued if the water heating savings are adequate.

    Technology types (resource)

    Discussion

    Efficiency

    The relative efficiency of heat pump water heaters and conventional systems are shown in Figure 6.

    whop1

    Relative efficiency of water heaters

    Contact us for a detailed list of manufacturers for this equipment.


    Pool Heating and Dehumidification Heat Pumps

    Use waste heat from heat producing equipment to heat swimming pools or spas. Some versions also provide indoor dehumidification and spot cooling.

    Pool heating heat pump

    Pool heating heat pumps use the vapor compression cycle to extract heat from the air for heating swimming pools or spas. Pool heating heat pumps must be constructed of special materials to resist corrosion. High-quality models incorporate coated evaporator coils, cupro-nickel heat exchangers, and corrosion-resistant cabinets specifically designed for pool environments. Pool heating heat pumps may be designed for outdoor or indoor installation.

    Pool heating heat pumps operate in a single mode for heating. In outdoor installation, the cooling effect is generally not utilized and is dissipated. In indoor installations the pool heating heat pump can provide some dehumidification and cooling. During winter this cooling effect may be unwanted.

    Pool heating and dehumidification heat pump

    Pool heating and dehumidification heat pumps are similar to pool heating heat pumps, but incorporate space cooling and dehumidification capabilities. Heat is used for heating the pool and, in some models, may also be used for space reheat as part of the dehumidification process. Units are designed for indoor or rooftop installation.

    Pool heating and dehumidification heat pumps operate in several modes, with pool heating/dehumidification being the most common. Other operating modes such as air conditioning, space heating, or ventilation may require additional components.

    Pool heating heat pumps operate in a single mode for heating.  Common operating modes for pool heating and dehumidification heat pumps include:

    • Pool heating with reheat - Heat and moisture are removed from the air inside the pool enclosure. A portion of the recovered heat is used for pool heating, the remainder is used to reheat the discharge air from the heat pump.
    • Pool heating without reheat - Heat and moisture are removed from the air inside the pool enclosure. All the recovered heat is used for pool heating, creating a net cooling effect in the enclosure.
    • Dehumidification - Heat and moisture are removed from the pool enclosure. All the recovered heat is used to reheat the leaving air. No pool heating is provided.
    • Dedicated space cooling - Heat and moisture are removed from the air inside the pool enclosure. All of the recovered heat is rejected through an auxiliary condenser to provide space cooling. An auxiliary condenser is required if the pool and indoor air are not heated.
    • Ventilation - The refrigeration circuit is not utilized. Outdoor air is supplied to the pool enclosure. Exhaust of pool enclosure air may be provided.

    Some units offer expanded space conditioning or water heating capabilities using energy from auxiliary sources, such as chilled water systems or heating elements. Air-side economizers may be used for cooling. Additional operating modes include:

    • Space cooling with economizer
    • Space cooling with condenser (air-cooled and water cooled condensers are common options)
    • Space cooling with auxiliary cooling (using chilled water coil)
    • Space heating with auxiliary heat (electric resistance, hot water coil, steam coil, and fuel-fired furnaces)
    • Supplemental water heating (using a second condenser or desuperheater)

    Applications

    • Most pools in conditioned or partially conditioned spaces could benefit from the application of a heat pump to heat the pool and reduce humidity levels in the enclosure.

    Possible applications

    • Indoor spas.
    • Heat pump water heaters may be economically justifiable in outdoor pools under utility rates in many areas.

    Efficiency

    Because the required water temperature for pool heating is low, 80° F to 85° F, heat pump water heaters can operate with excellent efficiency. A COP of 3.5 to 6.5 is typical. For applications with indoor evaporators, the warm, humid air in the pool enclosure provides an excellent heat source for the heat pump. The high wet-bulb temperature and moderate dry-bulb temperature result in excellent operating efficiency and output.

    Contact us for a detailed list of manufacturers for this equipment.

    Other information

    There are no performance standards for pool heating heat pumps or pool heating and dehumidification heat pumps. A standard is being developed for pool heaters. ASHRAE 146P, Methods of Testing for Rating Pool Heaters will apply to all pool heaters, including gas-fired, oil-fired, electric resistance, and electric air-source heat pumps. The proposed standard is expected to be released in 1998.


    Desuperheater and Refrigeration Heat Reclaim Units

    Use waste heat from cooling unit compressors to essentially provide free water heating energy (but only when the cooling unit is operating).

    A refrigeration heat reclaim (RHR) water heating system links two common functions in commercial buildings to reduce purchased energy consumption and achieve cost savings. A refrigeration heat reclaim water heating system harvests heat that would normally be rejected through refrigeration system condensers and applies the heat for water heating. See Figure 1. Refrigeration heat reclaim water heating has the advantages of relatively low cost and simplicity. The primary limitation of refrigeration heat reclaim water heating systems is the fact that heat is available only when the refrigeration system is in operation. However, in many applications heat storage capacity and the operating diversity of heat source equipment remove this concern.

    Note: "Refrigeration heat reclaim" refers to recovery of heat from direct expansion vapor compression cooling systems in general, including both food storage refrigeration and air conditioning. It is not limited to food storage freezers and coolers.

    5260701i

    Principle of refrigeration heat reclaim

    Desuperheaters are a particular type of refrigeration heat reclaim system that recovers only the more readily available superheat energy from the host system. They can be somewhat simpler than RHR systems that recover heat of condensation. Details are provided on the Operation page.

    A typical refrigeration heat reclaim system is shown in Figures 2 and 3. Most installations are designed as preheat systems using a separate storage tank in series with a conventional water heater. The refrigeration system to which the refrigeration heat reclaim system is connected is called the host system.

    5260702e

    Typical refrigeration heat reclaim system

    A refrigeration heat reclaim device is simply a refrigerant-to-water heat exchanger installed between the host refrigeration system's compressor and condenser. On heat pumps, the heat exchanger is installed between the compressor and the reversing valve. Water is circulated through one side of the heat exchanger and hot refrigerant gas from the compressor is routed through the other side. Heat is transferred from the hot refrigerant gas to the water.

    5260703e

    Refrigeration heat reclaim system operation on pressure-enthalpy diagram

    Most refrigeration heat reclaim devices are desuperheaters. Superheat refers to heat stored in the refrigerant vapor when it is heated above the temperature at which it evaporates for a given pressure. See Figure 3. Acting as a desuperheater, a heat reclaim device cools the refrigerant only to the saturation point; no condensing takes place in the desuperheater. Under typical conditions a desuperheater can remove about 10 to 30% of the total heat that would have been rejected by the condenser.

    A heat reclaim device may also be designed to do condensing rather than just desuperheating. More heat can be extracted, but at a lower temperature. However, most refrigeration heat reclaim equipment manufacturers have intentionally prevented condensing to avoid problems with host equipment operation. Excessive subcooling (reduction of liquid refrigerant temperature below the saturation point) in the condenser at low outdoor temperature is the concern. With excessive subcooling, problems can occur with low compressor head pressure, improper expansion device operation from inadequate pressure drop, and liquid slugging in the compressor.

    Most refrigeration heat reclaim units are designed for retrofit installation. Since installation involves cutting into the sealed refrigerant system, a qualified refrigeration mechanic should do the work. The effect of the installation on any warranties for the refrigeration system should be investigated. Some manufacturers of air conditioners and refrigeration systems place limitations on warranties if heat reclaim systems are installed.

    Applications

    • Refrigeration, freezer, water cooler, and ice maker compressors with long daily run time that operate throughout the year.
    • Applications on low-temperature refrigeration systems. They release more waste heat per ton of cooling effect than higher-temperature refrigeration systems.
    • Less efficient host systems in general. They provide more heat for recovery than more efficient units.

    Possible applications

    Where the addition of a RHR unit may improve the performance of the host machine. For example, the installation of a desuperheater in a Georgia fast food restaurant increased the capacity of the ice machine and eliminated ice runouts during the lunch period.

    Efficiency

    The potential heat output of a refrigeration heat recovery unit is determined by the amount of heat rejected from the host system. Lower-temperature host systems and less efficient host systems provide more heat than higher-temperature systems and more efficient systems.

    Refrigeration heat recovery from an HCFC-22 air-conditioning system will provide approximately 3000 Btu per ton-hour of host system output.

    Refrigeration heat recovery from an HFC-134a air-conditioning system will provide approximately 2200 Btu per ton-hour of host system output.

    Impact on refrigeration device

    It is sometimes claimed that refrigeration heat reclaim systems improve the host system efficiency as much as 20%, reduce electric demand, and increase the life of the compressor. These claims are often overstated. While a heat reclaim system can potentially improve compressor life, the degree of improvement has not been quantified. If installation is not done properly, the increased pressure drop in the refrigerant system can result in significant reduction of compressor life.

    Other information

    Standards

    ANSI/ARI 470-80 Standard for Desuperheater/Water Heaters establishes equipment specifications, procedures for testing and rating, safety provisions, and product labeling requirements for external heat exchanger systems [24].

    Refrigerant venting

    Strict regulations now govern the release of CFC refrigerants to the environment. Refrigerant must be recovered and careful, quality installation practices must be followed to eliminate leaks.

    Contact us for a detailed list of manufacturers for this equipment.


    Multifunction Full Condensing Units

    Use waste heat from cooling unit compressors to provide hot water heating energy, and still use for a standalone water heating if cooling is not needed.

    Multifunction, full-condensing systems are vapor compression cycle units that have several operating modes, including a water-heating-only mode. Terms such as "trifunctional" and "triple-function" are used by some manufacturers to describe these units. Their refrigerant-to-water heat exchangers are large enough to fully condense the refrigerant, and special controls are used to manage refrigerant inventory. Annual water heating COP ranges from 2.0 to 4.0, but can be much higher if waste heat from a cooling function is the primary heat source. Their primary disadvantage is their high initial cost.

    Multifunction full condensing units may operate in some combination of the following modes:

    • Dedicated space cooling
    • Space cooling and water heating
    • Dedicated space heating
    • Space heating and water heating
    • Dedicated water heating

    Multifunction, full-condensing systems (MFFCs) have two condensers, one for space heating and cooling and one for water heating. The water heating condenser is used when water heating is required; it is usually plumbed in parallel with the space heating condenser, although many variations are possible. Some systems are plumbed and controlled to allow the water heating condenser to be used either for full condensing or desuperheating.

    Multifunction, full-condensing systems are referred to as "full-condensing" because, unlike desuperheaters, they can apply all the waste heat energy produced in the cooling mode to water heating, not just the 10 to 30% contained in the superheated vapor. The ability to utilize all available waste heat, combined with the water-heating-only mode, means multifunction, full-condensing systems can supply much more high-efficiency water heating annually than desuperheaters. Supplementary water heating capacity is still required; but it is generally infrequently used.

    mffc

    Terms such as "trifunctional" and "triple-function" are confusing because they are used by some to describe desuperheaters, and by others to refer to multifunction, full-condensing systems. The terms "trifunctional" and "triple-function" are avoided here and in other EPRI publications.

    Advantages of MFFCs

    • Water heating output is higher than that of desuperheater water heaters.
    • Annual COP is higher than that of a conventional electric water heater or desuperheater. Annual water heating COP ranges from 2.0 to 4.0. Higher efficiency is possible if waste heat from a cooling function is the primary heat source.
    • Waste heat recovery rates in the space cooling/water heating mode are higher than for desuperheater water heaters.
    • Overcooling of interior spaces can be avoided by switching from indoor air to outdoor air for the heat source.
    • Diversified electric demand is lower than for conventional electric resistance water heaters.

    Disadvantages

    • First cost is higher than for desuperheater water heaters and some dedicated HPWHs
    • Controls are more complex than those in desuperheater water heaters, dedicated HPWHs, or many vapor-compression systems that do not heat water
    • "All-in-one" design means that high-efficiency water heating capability is lost if malfunctions occur elsewhere in the vapor compression cycle. (Backup water heating would still be available but would be less efficient.)

    There are a variety of multifunction, full-condensing units available for different applications.  All are capable of operating in two or more of the following modes, including at least one water heating mode.

    • Dedicated space cooling
    • Space cooling and water heating
    • Dedicated space heating
    • Space heating and water heating
    • Dedicated water heating

    MFFCs have two condensers, one for space conditioning and one for water heating, usually plumbed in parallel.  Heat is rejected through the water heating condenser when water heating is required.  Unlike desuperheaters, MFFCs can apply all of the condenser heat to the water heating load, not just the 10 to 30% available by desuperheating.  Their ability to do full-condensing water heating and their common dedicated water heating mode of operation allow MFFCs to provide a much greater portion of the annual water heating load than desuperheaters.

    Applications

    Multifunction, full-condensing units are best applied where there is a need for space conditioning and where the water heating load is large enough to permit regular operation of the system's high-efficiency water heating functions.

    Best applications

    • Residences, indoor pools, and restaurants. 

    Possible applications

    • Where there are significant water heating and space conditioning loads.

    Efficiency

    Because they are capable of many combinations of operating modes, it is difficult to define ratings that describe the performance of multifunction, full-condensing heat pumps. There are no established standards for these systems. One manufacturer obtained a waiver from US DOE to define a combined cooling performance factor or CCPF combined operation for cooling and water heating. A combined heating performance factor was defined for combined space heating and water heating. The CCPF and CHPF are similar to SEER and HSPF, respectively, with the water heating output of the heat pump added to the space conditioning output.

    Contact us for a detailed list of manufacturers for this equipment.

    Other information

    Multifunction, full-condensing units are not a well-defined product category. ARI Standard 290-96 establishes definitions, classifications, and testing and rating requirements for air conditioning and heat pump equipment incorporating potable water heating devices. This standard applies to air-source units with rated capacities less than 65,000 BTUH.


    Off-Peak Thermal Storage Water Heaters

    Store heat from heat producing equipment during peak activity periods to provide water heating energy at a later time.

    Thermal storage system configurations

    Off-peak water heaters usually have greater storage capacity than would be used in a conventional system for the application.  Off-peak water heating features and functions are often combined with systems designed for off-peak space heating or process heating. Both custom-made dedicated storage systems and systems assembled in the field from conventional components are used. The common operating pressure and temperature combinations are described by the following three categories:

    • Direct
    • Indirect-vented
    • Indirect-pressurized

    Direct storage systems

    Direct storage systems heat water directly in the storage tank or by an open loop to a remote boiler or other heat source. They are essentially simple storage water heating systems designed with controls to accomplish off-peak operating functions. Maximum operating temperature is about 200¡F. Direct systems can be assembled from conventional water heaters and storage tanks or they may be built particularly for the purpose. Smaller, off-peak storage systems built from conventional water-heating components may be less expensive. Dedicated packaged systems may include added insulation, connections for external control, and tank baffles or inlet headers to minimize mixing of the tank when cold water is introduced.

    Indirect-vented storage systems

    Several manufacturers build indirect thermal storage systems using tanks vented to the atmosphere, which ensures operation at atmospheric pressure and allows savings in tank costs. A typical indirect-vented storage system is shown in figure 1. Alternatively, a closed system with an expansion tank may be used and the system can still avoid the expense of ASME rated construction if it operates at less than 15 psig.  Indirect systems use the water in the tank only for thermal storage; potable water is heated either by an external heat exchanger or by a heat exchanger located inside the storage tank. Indirect, vented storage systems also operate at a maximum temperature of about 200¡F.

    5260502c

    Typical indirect, vented storage system

    Potable water circulated through the heat exchanger does not contact the water in the storage tank. Consequently, the thermal storage tank can be unlined since it is not subject to corrosion caused by the frequent exchange of oxygenated fresh make-up water. Furthermore, only the heat exchanger must be pressure rated. Tanks are constructed of steel or lightweight aluminum with an EDPM liner. Tanks are typically insulated with 2 to 2.5 inches of foam.

    The thermal storage tank is heated by electric resistance elements, usually flanged immersion-type elements, near the bottom of the tank. Multiple elements provide staged heating capacity and redundancy.  The elements are operated by electronic controllers through mercury switches or mechanical contactors. The controller can be interfaced to an energy management and controls system or to an electric utility control system for positive demand control.

    Indirect-pressurized storage systems

    Indirect-pressurized storage systems are supplied as packaged systems by several manufacturers. The systems are usually installed to meet both water heating and space heating loads. The elevated operating pressure and the volume of typical tanks requires that the tanks be built to ASME pressure vessel specifications, raising costs somewhat. However, other advantages may make them attractive for certain applications.

    A typical pressurized off-peak water heating system consists of a well-insulated sealed pressure vessel containing water treated to remove corrosion. Heat is supplied by immersion electric resistance elements or a steam heat exchanger located near the bottom of the tank. See figure 2. Unlike conventional direct storage systems, potable water does not flow through the tank. Instead, water is heated in a water-to-water heat exchanger, located either inside the tank or externally. Since the storage tank is a closed system, the continuing introduction of oxygen, minerals, and particulates that occur in the incoming cold water for open systems is avoided. Scaling, liming, and corrosion of the tank and elements are reduced, extending the overall life of the system and reducing maintenance costs. This configuration also allows the storage units to be connected to a space heating or process heating loop without the need to design the heating loop to accommodate potable water.

    5260503c

    Typical indirect, pressurized storage system

    Typical packaged systems operate at a maximum temperature of 250 to 300¡F and maximum working pressure from 65 to 160 psig. Depending on the temperature approach of the heat exchanger, energy can be delivered at tank temperatures as low as about 10 to 20¡F above the hot delivery temperature. Using the direct relationship between pressure and temperature in a closed system, a pressure controller operates the heating elements. Pressure control provides more rapid response and better representation of average tank temperature. Leaving water temperature is regulated by a mixing valve. A high limit temperature control and low water cutoff are provided as safety controls.  The tanks are heavily insulated and available in capacities from 200 to 18,000 gallons in vertical and horizontal configurations. Electric heating elements are available in capacities from 20 to 1000 kW.  A variety of steam heat exchanger capacities are available, subject to the steam system supply pressures and flow rate. Dual-fuel systems are used to provide redundant heat sources and to allow optimization of electric and steam loads.

    Since indirect-pressurized systems are provided as a package, design options usually involve only selection of thermal storage capacity, number and type of control of heating elements, operating voltage, control interface with the utility or an EMC or BAS, and selection of water heating and/or space heating capability.

    Thermal storage water heaters are typically applied for off-peak water heating. 

    In some commercial water heating applications, all water heating energy input can be shifted entirely to the electric utility's off-peak period by using additional thermal storage capacity and simple controls.  Figure 1 compares the operation of a conventional water-heating system and an off-peak system for a water heating load in a typical daytime commercial water heating load. Unlike off-peak space heating and air conditioning, off-peak water heating has the advantage of producing year-round benefits. Savings may also be available from reduced electric service entry and wiring size by keeping the water heating load off the facility peak.

    5260501d

    Benefits of off-peak water heating

    Indirect-pressurized systems

    For common hot supply water temperatures of about 140¡F, indirect-pressurized systems store about 50% more energy than conventional systems by relying on elevated temperature and pressure in the storage tank.  However, the energy storage density of indirect-pressurized systems operating at high temperatures is not always appreciably greater than that of conventional direct storage systems.  In fact, where the hot water supply temperature is 180¡F or more, indirect-pressurized systems may store less energy per gallon of storage volume.  The difference is a result of the heat exchanger approach and the fact that the required hot water delivery temperature is close to the temperature of the water in the tank.

    Applications

    • In facilities with central water heating systems where off-peak electric rates are available and facility operations allow off-peak heating and on-peak hot water usage.
    • To avoid increases in electric service capacity by limiting the demand of the water heating load during peak periods.

    Possible applications

    • For meeting both hot water and space heating loads in facilities with central HVAC and water heating systems.

    Efficiency

    Thermal storage water heating systems using elevated storage temperature may consume slightly more energy than conventional systems because of the increased heat loss from the tank.  In good applications, such small increases in operating costs are more than offset by savings from the use of lower-priced off-peak electricity.

    Operating cost savings for off-peak thermal storage water heaters are available only if the utility rate includes a provision for lower-cost off-peak service or where electric demand control incentives are available.

    Contact us for a detailed list of manufacturers for this equipment.

    Other information

    For pressurized systems, the elevated operating pressure and the volume of typical tanks requires that the tanks be built to ASME pressure vessel specifications, raising costs somewhat.



    Eliminate construction obstacles with these specs for three-phase, pad-mounted transformers.

    When a client requests underground service, one of the most common problems architects and engineers face is insufficient space. To help make your design planning a little easier, use these specifications for three-phase, pad-mounted transformers. Be sure to confirm the pad location with your local power company engineer prior to construction.

    General specifications for pad location

    1. Customer's service entrance cable and conduits should be installed in the open window of the concrete pad in the shaded area shown. Conduits should be installed starting at the extreme right-hand side of the window. Conduits should not be installed near the left-hand dimension of the shaded customer conduit window unless absolutely necessary.
    2. Grounding is to be provided by enhanced grounding consisting of 100 feet of #2 copper 7-strand conductor installed in the bottom of the trench and/or 30 foot sections of ground rod installed in both the primary and secondary sides of the concrete pad window. The ground rod locations are not dimensioned to allow maximum flexibility in locating the ground rods, but the separation between ground rods should be as great as possible.
    3. The transformer pad should not be located near fire hydrants, fire escapes, doors, windows, ventilation ducts, or under building overhangs. If possible the pad should be installed on ground that slopes away from the building. There should be no above ground obstructions such as air conditioners, walls, shrubbery, trash bins, etc. in front of the transformer location. The transformer location must be accessible by large truck or crane.
    4. There must be clear area around the transformer as detailed in the drawing below. The 10' x 10' area at the rear of the pad is necessary for the proper operation of the bayonet fuse of the transformer.
    gen_pad

    Are you investing your energy dollars wisely? An excellent way to analyze your energy investments is to compare your organization's energy spending against others in your industry. This Web page gives you the tools and information you need to make those comparisons for several different industry segments. You can also call on our consulting services to help analyze your energy usage and identify ways to save money and enhance operations.

    Features Advantages & benefits
    Energy comparisons for churches Examine typical energy spending in churches, including how each energy dollar is divided among the major energy consuming aspects of a church's operations.
    Energy comparisons for warehouses Examine typical energy spending in warehouses, including how each energy dollar is divided among the major energy consuming aspects of a warehouse's operations.
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    Energy comparisons for churches

    The tables and charts in this section present several different views of typical energy spending in Churches. Use each view as a "measuring stick" to gauge the quality of your own organization's energy spending.

    The Average End Use chart below presents the average Annual Energy Use Average information above as a graph (which visually shows the relative amounts of energy usage by each equipment type).

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    Energy comparisons for warehouses

    The tables and charts in this section present several different views of typical energy spending in Warehouses. Use each view as a "measuring stick" to gauge the quality of your own organization's energy spending.

    The Average End Use chart below presents the average Annual Energy Use Average information above as a graph (which visually shows the relative amounts of energy usage by each equipment type).



    Healthcare

    Compare your energy spending & usage to Healthcare industry averages

    Are you investing your energy dollars wisely? An excellent way to analyze your energy investments is to compare your organization's energy spending against others in your industry. This Web page gives you the tools and information you need to make those comparisons. In addition, you can call on our consulting services to help analyze your energy usage and identify ways to save money and enhance operations.

    Features Advantages & benefits
    Features Advantages & benefits
    Energy comparisons for hospitals Examine typical energy spending in hospitals, including how each energy dollar is divided among the major energy consuming aspects of a hospital's operations.
    Energy comparisons for nursing homes Examine typical energy spending in nursing homes, including how each energy dollar is divided among the major energy consuming aspects of a nursing home's operations.
    Energy comparisons for doctors' offices Examine typical energy spending in doctors' offices, including how each energy dollar is divided among the major energy consuming aspects of a doctor's office's operations.

    Energy comparison for hospitals

    The tables and charts in this section present several different views of typical energy spending in Hospitals. Use each view as a "measuring stick" to gauge the quality of your own organization's energy spending.

    The Average End Use chart below presents the average Annual Energy Use Average information above as a graph (which visually shows the relative amounts of energy usage by each equipment type).

    hospend2

    Energy comparisons for nursing homes

    The tables and charts in this section present several different views of typical energy spending in nursing homes. Use each view as a "measuring stick" to gauge the quality of your own organization's energy spending.

    The Average End Use chart below presents the average Annual Energy Use Average information above as a graph (which visually shows the relative amounts of energy usage by each equipment

    nursend2

    Energy comparisons for doctors' offices

    The tables and charts in this section present several different views of typical energy spending in doctors' offices. Use each view as a "measuring stick" to gauge the quality of your own organization's energy spending.

    The Average End Use chart below presents the average Annual Energy Use Average information above as a graph (which visually shows the relative amounts of energy usage by each equipment type).

    docend2

    Education

    Compare your energy spending & usage to industry averages.

    Are you investing your energy dollars wisely? An excellent way to analyze your energy investments is to compare your organization's energy spending against others in your industry. This Web page gives you the tools and information you need to make those comparisons for several different industry segments. You can also call on our consulting services to help analyze your energy usage and identify ways to save money and enhance operations.

    Features Advantages & benefits
    Energy Comparisons for Primary & Secondary Schools Examine typical energy spending in primary, middle, and secondary schools, including how each energy dollar is divided among the major energy consuming aspects of a school's operations.
    Energy Comparisons for Colleges & Universities Examine typical energy spending in colleges and universities, including how each energy dollar is divided among the major energy consuming aspects of a college or university's operations.
    Let us help Utilize our extensive expertise to analyze your facility's energy usage and identify possible ways to save money and enhance operations.

    Energy comparisons for schools (primary through secondary)

    The tables and charts in this section present several different views of typical energy spending in Primary, Middle, and Secondary Schools. Use each view as a "measuring stick" to gauge the quality of your own organization's energy spending.

    The Average End Use chart below presents the average Annual Energy Use Average information above as a graph (which visually shows the relative amounts of energy usage by each equipment type).

    schend1

    Energy comparisons for colleges and universities

    The tables and charts in this section present several different views of typical energy spending in Colleges and Universities. Use each view as a "measuring stick" to gauge the quality of your own organization's energy spending.

    The Average End Use chart below presents the average Annual Energy Use Average information above as a graph (which visually shows the relative amounts of energy usage by each equipment type).

    collend2

    Let us help with a facility analysis

    New technologies and methods are constantly arising that can reduce your facility's energy spending and enhance operations. We maintain a staff of specialized professionals who constantly monitor trends and advances in various industries' operations, energy management, and production technologies. You can arrange for a representative from this team to help analyze your facility's operations and energy usage to reduce energy costs and improve efficiency. To arrange for a free initial analysis, contact us.


    Food Service

    Compare your energy spending & usage to Food Service industry averages.

    Are you investing your energy dollars wisely? An excellent way to analyze your energy investments is to compare your organization's energy spending against others in your industry. This Web page gives you the tools and information you need to make those comparisons. In addition, you can call on our consulting services to help analyze your energy usage and identify ways to save money and enhance operations.

    Features Advantages & benefits
    Energy Comparisons for Full Service Restaurants Examine typical energy spending in Full Service restaurants, including how each energy dollar is divided among the major energy consuming aspects of a restaurant's operations.
    Energy Comparisons for Fast Food Restaurants Examine typical energy spending in Fast Food restaurants, including how each energy dollar is divided among the major energy consuming aspects of a restaurant's operations.

    Energy comparison for full service restaurants

    The tables and charts in this section present several different views of typical energy spending in Full Service restaurants. Use each view as a "measuring stick" to gauge the quality of your own organization's energy spending.

    The Average End Use chart below presents the average Annual Energy Use Average information above as a graph (which visually shows the relative amounts of energy usage by each equipment type).

    Image4

    Energy measuring sticks for fast food restaurants

    The tables and charts in this section present several different views of typical energy spending in Fast Food restaurants. Use each view as a "measuring stick" to gauge the quality of your own organization's energy spending.

    The Average End Use chart below presents the average Annual Energy Use Average information above as a graph (which visually shows the relative amounts of energy usage by each equipment type).

    Image7

    Retail

    Compare your energy spending against others in the Retail and Office Building industries.

    Compare your energy spending against others in the Retail and Office Building industries

    Are you investing your energy dollars wisely? An excellent way to analyze your energy investments is to compare your organization's energy spending against others in your industry. This Web page gives you the tools and information you need to make those comparisons. In addition, you can call on our consulting services to help analyze your energy usage and identify ways to save money and enhance operations.

    Features Advantages & benefits
    Energy comparisons for Retail Stores Examine typical energy spending in hospitals, including how each energy dollar is divided among the major energy consuming aspects of a retail store's operations.
    Energy Comparisons for Grocery Stores Examine typical energy spending in grocery stores, including how each energy dollar is divided among the major energy consuming aspects of a grocery store's operations.
    Energy Comparisons for Convenience Stores Examine typical energy spending in convenience stores, including how each energy dollar is divided among the major energy consuming aspects of a convenience store's operations.
    Energy comparisons for Office Buildings Examine typical energy spending in small, medium, and large office buildings, including how each energy dollar is divided among the major energy consuming aspects of an office building's operations.

    Energy comparisons for retail stores

    The tables and charts in this section present several different views of typical energy spending in Retail Stores. Use each view as a "measuring stick" to gauge the quality of your own organization's energy spending.

    The Average End Use chart below presents the average Annual Energy Use Average information above as a graph (which visually shows the relative amounts of energy usage by each equipment type).

    retend2

    Energy comparisons for grocery stores

    The tables and charts in this section present several different views of typical energy spending in Grocery Stores. Use each view as a "measuring stick" to gauge the quality of your own organization's energy spending.

    The Average End Use chart below presents the average Annual Energy Use Average information above as a graph (which visually shows the relative amounts of energy usage by each equipment type).

    groend2

    Energy comparisons for office buildings

    The tables and charts in this section present several different views of typical energy spending in office buildings. Use each view as a "measuring stick" to gauge the quality of your own organization's energy spending.

    Note that energy use differs significantly depending on the size of an office building. Therefore, this section presents separate tables and charts for small, medium, and large office buildings. Comparing these tables and charts to one another can provide interesting insights into the effect that office building size has on energy usage.

    The Average End Use charts below present the average Annual Energy Use Average information above as a graph (which visually shows the relative amounts of energy usage by each equipment type). Note that energy use distribution differs for small, medium, and large office buildings.

    smend2
    medend2
    larend2

    Hospitality

    Compare your energy spending against others in the Hospitality industry.

    Compare your energy spending against others in the hospitality industry

    Are you investing your energy dollars wisely? An excellent way to analyze your energy investments is to compare your organization's energy spending against others in your industry. This Web page gives you the tools and information you need to make those comparisons. In addition, you can call on our consulting services to help analyze your energy usage and identify ways to save money and enhance operations.

    Features Advantages & benefits
    Energy Comparisons for Low-Rise Hotels and Motels Examine typical energy spending in low-rise hotels and motels, including how each energy dollar is divided among the major energy consuming aspects of a low-rise hotel or motel's operations.
    Energy Comparisons for Full Service Restaurants Examine typical energy spending in Full Service restaurants, including how each energy dollar is divided among the major energy consuming aspects of a restaurantÕs operations.

    Energy comparisons for low-rise hotels and motels

    The tables and charts in this section present several different views of typical energy spending in Low-Rise Hotels and Motels. Use each view as a "measuring stick" to gauge the quality of your own organization's energy spending.

    The Average End Use chart below presents the average Annual Energy Use Average information above as a graph (which visually shows the relative amounts of energy usage by each equipment type).

    hosend2

    Energy comparison for full service restaurants

    The tables and charts in this section present several different views of typical energy spending in Full Service restaurants. Use each view as a "measuring stick" to gauge the quality of your own organizationÕs energy spending.

    The Average End Use chart below presents the average Annual Energy Use Average information above as a graph (which visually shows the relative amounts of energy usage by each equipment type).

    image4-restaurants