What Are Geothermal Heat Pumps?
Geothermal heat pumps, also known as ground-source heat pumps, use
the constant temperature of the earth as the exchange medium instead of
the outside air temperature. This allows the system to reach fairly high
efficiencies (200%-400%) on the coldest of winter nights, compared to 175%-250%
for air-source heat pumps on cool days.
While many parts of the country experience seasonal temperature extremes—from scorching heat in the summer to sub-zero cold in the winter—a few feet below the earth's surface the ground remains at a relatively constant temperature. Like a cave, this ground temperature is warmer than the air above it during the winter and cooler than the air in the summer. The geothermal heat pump takes advantage of this by transferring heat stored in the earth or in ground water into a building during the winter, and transferring it out of the building and back into the ground during the summer. The ground, in other words, acts as a heat source in winter and a heat sink in summer.