Geothermal Heat Pump

A geothermal heat pump, also called a ground source heat pump, is a heating and cooling system that uses a heat pump to move heat to or from the ground, taking advantage of the fact that temperatures a few meters underground stay relatively stable across the seasons, typically around 7 to 12 degrees Celsius at six meters depth in the northern United States. Buried pipework, usually high density polyethylene carrying water mixed with antifreeze, forms a ground heat exchanger that lets the system extract heat from the ground in winter and dump heat into it in summer. The idea traces to a heat pump concept Lord Kelvin described in 1853 and a 1912 patent by Heinrich Zoelly for drawing heat from the ground, and the first commercial installation opened at the Commonwealth Building in Portland, Oregon in 1948; a typical unit has a coefficient of performance of three to six, delivering three to six units of heat for every unit of electricity it consumes, and by 2004 more than a million units were installed worldwide.