During the summer, the systems pump indoor heat underground and draw on the lower temperatures of the Earth to cool a building. In colder months, the same process works in reverse, with heat from the ground being used to warm indoor air.
Indoors are box-shaped heat pumps that pull and and push either water or a working fluid, such as antifreeze, in and out of the ground. Using the same compressor loop mechanism that a refrigerator has, a heat exchanger draws energy from the circulating liquid to either heat or cool a building.
There are a number of different configurations for the liquid transfer loops--either water wells several hundred feet deep, which are said to be the most efficient, or coils which could be dug only a few meters underground. Others use a body of water like a pond as a heat sink.
Regardless of type, though, ground-source heat pumps are considered one of the most efficient forms of heating and cooling.
The International Ground Source Heat Pump Association, based in Stillwater, Oklahoma, said geothermal is 50 percent to 70 percent more efficient for heating than other systems. The U.S. Department of Energy says that a ground-source heat pump uses 25 percent to 50 percent less electricity than conventional heating and cooling systems."
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