DOE EERE Research Reports

Electrically-Driven Heat Pumps

ACES, Electric Heat Pumps, Dynamic Losses, Refrigerants and Fluid Development, Geothermal (Ground Coupled) Heat Pumps

Almost all residential and small commercial heat pumps and air conditioning systems in the U.S. use an electrically-driven compressor in equipment using the reverse Rankine, or vapor compression, cycle to move heat from one place to another. To provide space heating, a cold low pressure mixture of liquid and vapor absorbs heat from warmer outdoor air causing it to boil and form a cold low pressure single-phase vapor. The vapor is compressed forming hot high pressure vapor that condenses rejecting heat to the cooler indoor air. Projects to improve heating and cooling efficiency were undertaken in advanced cycle development, working fluids, and interseasonal energy storage.

Electrically driven heat pumps are commonly used for heating and cooling homes in the mid-latitude regions of the United States. Single-speed, air-to-air electrically driven heat pumps extract energy from the outdoor air on winter and fall days and use a relatively small amount of electricity to "pump" the heat into homes and businesses. Geothermal heat pumps (ground coupled heat pumps) perform the same task but extract heat from the ground, ground water, or surface water near the building. During the hot summer months, these same electrically driven heat pumps and geothermal heat pumps extract heat from inside buildings to cool them and reject the heat to the surrounding air or ground. The ACES or Annual Cycle Energy System is an interseasonaly energy storage system that extracts or rejects heat to a storage bin full of water, producing ice during the winter that can satisfy most or all of the building's air conditioning needs. ACES was demonstrated to be highly energy efficient during the 1980's but did not result in successful commercial products at that time because of very low prevailing energy costs. Refrigerant fluid development focused on the development of azeotropic and non-azeotropic refrigerant mixtures to improve heat pump and refrigeration cycle efficiency and as replacements for CFCs and HCFCs that damage levels of stratospheric ozone.


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