It's not the heat, it's the humidity. Often, summertime comfort is not only a function of outdoor temperature but also of relative humidity. During the cooling season, given equal air temperature, people often feel more comfortable at a lower relative humidity. Desiccants remove moisture to improve comfort, air quality, and energy efficiency. Typically, air that is dried by desiccants is subsequently cooled by an air conditioner or evaporative cooler.
Desiccant materials, which absorb moisture, can be dried, or regenerated, by adding heat supplied by natural gas, waste heat, or the sun. In most systems, a wheel that contains a desiccant turns slowly to pick up humidity from incoming air and discharge that humidity to the outdoors. A desiccant system can be combined with a conventional air conditioning system in which the desiccant removes humidity and the air conditioner lowers air temperature.
The use of desiccant cooling for residential use is being explored in conjunction with energy recovery ventilators (ERV). An energy recovery ventilator is designed to provide energy recovery in a mechanical ventilation system during the heating season. ERVs recover heat and humidity from indoor air to preheat and humidify incoming fresh air. Desiccant cooling is designed to dehumidify incoming fresh air in the summer. Combined, they make a year-round energy recovery device for homes with mechanical ventilation.
Because mechanical ventilation replaces conditioned air from inside a home with unconditioned (hot in summer, cold in winter) air from the outside, energy recovery devices which recapture some of that exiting energy improve the efficiency of mechanical ventilation.
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By reducing humidity entering homes, occupants feel more comfortable at slightly higher temperatures. Therefore, occupants can reduce cooling energy consumption by raising the thermostat setpoint.
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By reducing humidity, desiccant systems improve indoor air quality and the potential for mold growth. Outside the home, desiccant technology reduces power plant emissions.
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High initial cost might deter the use of desiccant cooling systems. A combined ERV-desiccant cooling system would be most applicable in areas of the country that have humid summers and dry, cool winters.
Desiccant cooling systems are not commercially available for residential applications. However, a combined ERV and desiccant cooling system is in the development stage.
A combined ERV and desiccant cooling system is projected to cost about $1700.
According to the National Renewable Energy Laboratory, desiccant dehumidification could reduce total residential electricity demand by as much as 25 percent in humid regions.
The Air-Conditioning and Refrigeration Institute (ARI) has published a new standard, ARI Standard 940-98 "Desiccant Dehumidification Components," that applies to thermally regenerated desiccant components.
If gas is used for desiccant regeneration, proper venting will be required to eliminate air quality concerns.
Not Applicable
Desiccant cooling wheels could be situated through the wall or attached to ductwork. The incoming air could be ducted to the home's air conditioning supply.
Not Applicable
As part of a mechanical ventilation system, desiccant cooling systems decrease cooling energy needs and increase comfort. Mechanical ventilation improves indoor air quality and desiccant cooling helps further improve air quality by lowering humidity and removing potential pollutants. In addition, people may increase their air conditioning set point when air feels more dry.
Desiccant cooling does not use chlorofluorocarbons (CFCs), a refrigerant that is linked to ozone depletion.
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