Most Common Geothermal Systems

Geothermal

• The theory behind geothermal heat pumps is that the temperature beneath the surface of the ground or water is cooler than that of the air in the summer and warmer than the cold winter air. Depending on the season and the climate in which a building is situated, the temperature a few feet beneath the surface of the ground or water in the U.S. can range from around 45F to around 75F. Geothermal systems can be used to supply heat, cool air and hot water for a building, with the higher installation costs of a geothermal system repaid to the owner in between 5 and 10 years in energy savings over other types of heating systems. The winter efficiency rating of a geothermal system ranges between 300 and 600 percent, while other forms of heating systems have a winter efficiency rating of between 175 and 250 percent, according to the U.S. Department of Energy.

Residential

• Closed loop geothermal systems commonly used in residential heating systems are horizontal systems and pond/lake systems. The pond/lake system is the most efficient where a large body of water is located close to a building and regulations regarding water use can be met. The pond/lake geothermal system requires pipes to be laid under the surface of a body of water at least eight feet beneath the surface to avoid problems with freezing temperatures. Heating liquid is passed through these pipes to a heat pump located in the building where heat is transferred into the liquid. A horizontal geothermal system requires two pipes to be laid beneath the ground surface, between four and six feet deep, allowing the geothermal heating fluid to be looped around the piping for heat exchange to take place between the constant temperature of the soil and the heating fluid.

Vertical

• Large commercial buildings and complexes such as schools often use the vertical closed loop heating system in areas where land around the building is in short supply. In this system, small holes are drilled 100 to 200 feet into the ground, into which two pipes are inserted with a u bend to complete the closed loop. The pipes in each of the holes are connected by a series of pipes just below the surface of the Earth that connects to a geothermal heat pump within the building.

Open Loop

• The open loop geothermal system uses the water contained within a well or body of water to circulate through a series of pipes and the heat pump within a building. This system requires a large supply of water to be available throughout the year to maintain the heating and cooling abilities of the heat pump.