Natural Gas - Engine Driven Chillers | My Business | Mississippi Power | A Southern Company

Natural Gas - Engine Driven Chillers

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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.