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Novel design yields energy-efficient air conditioner

Researchers at the National Renewable Energy Laboratory are working on an energy-efficient air conditioner that breaks with conventional mechanics.

Abandoning the mechanics common in today's air conditioners could slash energy use and summertime electricity bills, according to the National Renewable Energy Laboratory.

Researchers at NREL recently detailed an air conditioning system that does away with the power-hungry condenser and compressor in traditional air conditioners. The goal is to further develop the technology and license it to commercial companies, something that NREL has already done in solar, wind, and other fields.

NREL engineer Eric Kozubal holds an air flow of an efficient air conditioner prototype that promises to cut energy use by as much as 75 percent in certain climates. National Renewable Energy Laboratory

Called the DEVap (Desiccant-Enhanced eVaporative) air conditioner, the system uses a combination of techniques to deal with both dry heat and humidity.

The system uses an evaporative cooler, which creates cool air by evaporating water from a wet surface with a fan, and combines the cooler with a dessicant to make dry air.

"Having a drying technology and a cooling technology that we can control however we wish (lets you) now have better control over your air," NREL scientist Jay Burch told 9News in Colorado.

The NREL air conditioner is an indirect evaporative cooler in which there are two air streams, NREL mechanical engineer and co-inventor Eric Kozubal told Technology Review. Water passes through one air stream to make it cooler and wetter. That conditioned air cools a membrane that cools the other air stream without adding water.

In another step, the system uses a dessicant that absorbs water from the air to reduce the humidity in a room. Rather than use the pebble-size dessicants typically found in packaging, the NREL system uses a liquid dessicant made out of syrupy aqueous solutions, such as lithium chloride or calcium chloride, which absorbs water vapor to create dry air.

"We bring the water and liquid desiccant into DEVap's heat-mass exchanger core. The desiccant and evaporative cooling effect work together to create cold-dry air," Kozubal said in a June 11 release describing the technology.

One of the advantages of such a system would be that it eliminates the need for harmful chlorofluorocarbons (CFCs) or hydrochlorofluorocarbons (HCFCs) used in refrigerant-based air conditioners.

The system would have different effectiveness in different areas, since evaporative coolers work best in dry rather than humid climates. But dessicant-based cooling, which is used in more expensive industrial drying processes, gives control over humidity to make air comfortable. The design could lower energy consumption by 25 percent to 75 percent, compared with conventional air conditioners, Burch told 9News.

The goal is to build a system that is cost competitive with today's air conditioners It will take three to five years before the technology can be commercialized, according to NREL.

Because air conditioning is such a significant load on the electricity grid and people's monthly bills, there are a number of companies trying to develop more efficient approaches to cooling, including solar-powered air conditioners that work during times of peak demand.