Engineers at Oregon State University in Corvallis, Ore., have found a way to take waste heat and use it to run a cooling system - a method that can improve the energy efficiency of diesel engines and perhaps some day appear in industry, automobiles and homes.

The heat-actuated cooling system, which will probably find its first applications by the U.S. Army, could ultimately be applied to factories or other places where waste heat is generated and used to provide either air-conditioning or electricity. In its first military application, where stationary diesel generator sets are used, researchers say they expect improved efficiencies of 20 to 30 percent where cooling is needed.

The system is one of the early applications of microchannel technology being developed by OSU and the Pacific Northwest National Laboratory in Richland, Wash., through a joint venture called the Microproducts Breakthrough Institute.

“Our approach will provide a capability that has not yet been achieved for efficiently using waste heat with small-scale systems,” says Richard Peterson, an OSU professor of mechanical engineering, noting that the technology has been successfully developed and a working prototype could be ready for demonstration by the second half of 2009.

Conceptually, the system works somewhat like existing heat pumps, but it is powered by waste heat, not electricity. What makes the technology unique, according to its developers, is the use of microchannel heat transfer components and an efficient “vapor expander” to provide high heat transfer rates and smaller, lighter and more efficient heat exchangers.

“Right now, about 75 percent of the fuel energy in most stationary diesel generators used to produce electricity is lost in the form of waste heat,” Peterson says. “The military often needs these generators to operate air-conditioning for advanced electronic equipment and other applications. So, we’re using that waste exhaust heat to drive an expander-compressor cycle that provides cooling.”

Industrial applications to improve energy efficiency are clearly possible - basically, anywhere significant amounts of heat are being produced but not used. While the early applications may be most readily developed with waste heat, it also could be possible to use this technology with heat that is intentionally produced such as with moderately concentrated solar energy to provide a building’s air-conditioning on hot, sunny days.

“This technology would allow you to produce electricity or cooling whenever something is hot, [so] it might be an ideal complement to a ‘smart’ energy system that could provide extra power during peak demand periods,” Peterson says. “We can now take heat and use it to create either electrical power, heat or cooling. It’s not yet clear what all the possible applications will be.”

OSU, through the Microproducts Breakthrough Institute, already can produce the microchannel devices needed to make this system operational, but work will continue in order to develop improved manufacturing efficiencies and to create less expensive devices at higher production volumes.

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