General info. High efficiencies (300%-600%) on the coldest of winter nights, compared to 175%-250% for air-source heat pumps on cool days.
Geothermal heat pumps (GHPs) can make use of the stable temperatures in the upper 10 feet of the Earth to provide both heating and cooling to buildings. The surrounding soil, groundwater, or nearby surface water is used as a heat source in winter and a heat sink in summer.
GHP systems consist of three parts: the ground heat exchanger, the heat pump unit, and the air delivery system (piping and ductwork). In winter, when the ground is warmer than the air, the geothermal heat pump removes heat from the ground heat exchanger and pumps it into the indoor air delivery system. In summer, when the ground is cooler than the air, the process is reversed and the geothermal heat pump moves heat from the indoor air stream into the ground heat exchanger.
Geothermal heat pumps reduce both heating and cooling costs compared to air source heat pumps and air conditioners in both residential and commercial buildings. They have low operating and maintenance costs and, usually, the lowest life-cycle costs of the available heating and cooling options. Consumption of electricity is reduced 25% - 50% compared to traditional heating and cooling systems, allowing a payback of system installation costs in 0 - 10 years.
Called by a variety of names—earth-source heat pumps, GeoExchange systems, ground-coupled heat pumps, ground-source heat pumps, and water-source heat pumps—GHPs are known for their low environmental impact, quiet operation, and energy efficiency. Today, more than 500,000 geothermal heat pumps have been installed nationwide, including more than 500 in schools.
Geothermal heat pumps (sometimes referred to as GeoExchange, earth-coupled, ground-source, or water-source heat pumps) have been in use since the late 1940s. Geothermal heat pumps (GHPs) 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 (300%-600%) 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. Depending on latitude, ground temperatures range from 45°F (7°C) to 75°F (21°C). 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 GHP takes advantage of this by exchanging heat with the earth through a ground heat exchanger.
As with any heat pump, geothermal and water-source heat pumps are able to heat, cool, and, if so equipped, supply the house with hot water. Some models of geothermal systems are available with two-speed compressors and variable fans for more comfort and energy savings. Relative to air-source heat pumps, they are quieter, last longer, need little maintenance, and do not depend on the temperature of the outside air.
A dual-source heat pump combines an air-source heat pump with a geothermal heat pump. These appliances combine the best of both systems. Dual-source heat pumps have higher efficiency ratings than air-source units, but are not as efficient as geothermal units. The main advantage of dual-source systems is that they cost much less to install than a single geothermal unit, and work almost as well.
Even though the installation price of a geothermal system can be several times that of an air-source system of the same heating and cooling capacity, the additional costs are returned to you in energy savings in 5–10 years. System life is estimated at 25 years for the inside components and 50+ years for the ground loop. There are approximately 40,000 geothermal heat pumps installed in the United States each year.
eere.energy.gov
