Desiccant Heat Pumps | My Business | Mississippi Power | A Southern Company

Desiccant Heat Pumps

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.