Residential geothermal systems take advantage of the Earth as a free heat source. A heat exchange and transfer process forms a ground loop system. The types of residential ground loop systems are closed loop and open loop. Closed-loop options include horizontal, vertical, or pond/lake. Vertical systems are mainly used commercially for large buildings.
A geothermal system uses a heat pump to take heat from underground fluid—usually water—and transfer it to duct work. For cooling, the reverse happens. The ducts distribute the heated or cooled air throughout a home's space.
Horizontal installations are appropriate for new-home construction, if land space is ample. Trenches are required for buried side-by-side pipes. Looping the pipes like coils in a shorter trench can decrease installation costs. This method also allows a geothermal system to fit in an area otherwise space-prohibitive of horizontal installation.
Homes with an on-site body of water can install the low-cost pond/lake type of system. A pipe runs underground from the house to the pond or lake. This supply pipe should be buried at least 8 feet (2.4 m) so it never freezes. The coiled circles of pipe are placed in the body of water. It is important that the pond or lake constantly maintain a minimum depth, quality, and volume.
Open-loop residential geothermal systems use water from a well or a body of water. This water is used as the heat exchange agent, which circulates through the system then returns to the ground via a well or surface discharge. Recharge wells are sometimes used for this return function. Open-loop systems are appropriate only when the water supply is clean, as the water supply must meet local groundwater discharge standards.
In addition to heating and cooling a home's spaces, residential geothermal systems can efficiently heat domestic water. These systems are equipped with desuperheaters, which use extra heat from the geothermal heat pump for the house's hot water tank. Geothermal heat pump manufacturers now offer full-demand systems for hot water on demand. These systems supply hot water even when the geothermal system is not operating.
All types of residential geothermal systems must be professionally installed. Accredited installers, trainers, and certified designers can be located through professional associations such as the International Ground Source Heat Pump Association (IGSHPA). These associations should be able to provide local contractors listed by area.
The best residential geothermal system for a home depends on the site's climate, available land space, and soil conditions. With thoughtful professional design and installation, residential geothermal systems can provide long-term energy savings.