Heat naturally moves from warmer places to cooler places. Heat pumps use electricity to move heat from cooler places to warmer places, making the cool space cooler and the warm space warmer. Your refrigerator is a heat pump, moving heat from inside the refrigerated cabinet into your kitchen. An air conditioner is a heat pump, moving heat from inside your home to the hot outside summer air.
Heat pumps are also used to heat homes and businesses. While air-source heat pumps extract heat from the outdoor air, a ground-source heat pump (GSHP) takes advantage of the fact that a few feet below the earth's surface the ground remains at a relatively constant temperature. Depending on latitude, ground temperatures range from 45°F to 75°F. Like a cave, this ground temperature is warmer than the air above it during the winter and cooler than the air in the summer. This leads to the exceptionally high efficiency of GSHPs.
GSHP systems consist of three parts: the ground-loop heat exchanger, the heat pump unit, and the air or water (hydronic) delivery system (ductwork or piping throughout a home or building). The ground-loop heat exchanger is a system of tubes called a loop, which is buried in the ground near the building. A fluid (usually a mixture of water and environmentally friendly antifreeze) circulates through the tubing to absorb or relinquish heat within the ground.
In the winter, the heat pump unit extracts heat from the heat exchanger and pumps it into the indoor air or hot water delivery system, moving heat from the ground to the building's interior. In the summer, the process is reversed, and the heat pump moves heat from the indoor air into the heat exchanger, effectively moving the heat from indoors into the ground.