Geothermal heat pumps, or geoexchange systems, are the most common form of geothermal energy used in homes and commercial buildings. Heat is removed from a substrate during the winter to heat a building and then during the summer the heat is removed from the building and put back into the substrate. The substrate is usually the earth but can also be water. A mix of water and antifreeze is used as the heat transfer fluid.
Closed loop systems include horizontal, vertical, and pond/lake systems. These systems are all self-contained, with the liquid heat transfer fluid never coming in contact with the earth or pond/lake. Closed loop systems receive their name from the piping configuration used to collect and disperse the heat from the substrate.
Horizontal systems use a series of pipes laid horizontally in a trench through which the heat transfer fluid is circulated. The pipes can also be looped in a “slinky” configuration to utilize a smaller trench.
Vertical systems are typically used in existing residential areas or for commercial buildings where long horizontal trenches are not an option because of land constraints. A series of vertical holes are drilled about 20 feet apart and 100-400 feet deep. The piping is placed in the holes with a U-bend at the bottom of each hole. The holes are all connected together to form the system.
The pond/lake system is similar to the horizontal system but requires a pond/lake of certain dimensions. Coils of pipes are placed at least eight feet below the surface (to prevent freezing) through which the heat transfer fluid is circulated. This is the least costly method as it does not require drilling.
In each of these systems, the heat transfer fluid passes through the substrate, goes into a building heat exchanger, and the resulting heat or cold is distributed through the building by a forced air or hydronic distribution network.