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Geothermal Heat Pumps

Photo of an elementary school.

Cavett Elementary School is one of several schools in Lincoln, Nebraska, to use geothermal heat pumps for heating and cooling.

Geothermal energy is heat from the Earth. Geothermal heat pumps use the relatively constant temperature of the ground or surface water as a heat source and sink for a heat pump, which provides heating and cooling for buildings. Geothermal heat pumps (GHPs) have been supplying homes and small businesses with heat, space cooling, and hot water for buildings and pools for more than 20 years.

There are two types of heat pumps: ground source and water source. Ground source heat pumps use buried loops or coils of tubing to exchange heat. Water source pumps use loops submerged in a lake or pond.

GHPs are known as earth-source heat pumps, GeoExchangeSM systems, ground-coupled heat pumps, ground-source heat pumps, or water-source heat pumps, and have low environmental impact, quiet operation, and energy efficiency. Surveys show a 90% owner satisfaction for these systems.

The basic elements of a GHP system are:

  • Ground loop — system of fluid-filled plastic pipes buried in the shallow ground, or placed in a body of water, near the building.

  • Heat pump — removes heat from the fluid in the pipes, concentrates it, and transfers it to the building. For cooling, this process is reversed.

  • Air delivery system — conventional ductwork used to distribute heated or cooled air throughout the building.

GHPs are initially more expensive to install than conventional heating systems, but if properly sized and installed, GHPs deliver more energy per unit consumed than conventional systems. Moreover, since geothermal heat pumps are generally efficient, they are less expensive to operate and maintain than conventional systems. Typical annual energy savings are 30%-60%. Depending on climate and soil conditions, system features, and financing and incentives, the payback may be 2-10 years through lower utility bills.

On average, a GHP system costs $2,500-$3,500 per ton of capacity. For average homes and businesses, DOE's Federal Energy Management Program estimates a ton of capacity for every 550 ft2 in heating-dominated climates, and a ton for every 450 ft2 in cooling-dominated climates. (One ton of capacity is equal to the heat required to melt 2,000 pounds of ice in 24 hours, or 12,000 Btu per hour.) A system that uses horizontal ground loops will generally cost less that one with vertical loops.

DOE's Geothermal Technologies Program has more information on geothermal heat pumps.

The Geothermal Heat Pump Consortium is another source of information on geothermal heat pumps.