This month, by request, I am discussing the basics of Geothermal Heat Pumps (also known as ground source heat pumps). While the initial expense associated with the installation is about twice (or more) than a typical air to air system, the cost to operate this system is considerably less. The payback in energy cost savings offsets the installation costs.

Geothermal Heat Pumps use typical vapor compression to move heat just like air to air units. However, the key difference is the reliability of the heat source/dump. Air to air systems rely on outdoor air temperature as a source/dump which varies depending on the season, where you live etc. With air to air systems the exterior temperature can get cold enough that it drops below the “balance point” of the equipment. Not so in geothermal systems as they use soil as a heat source/dump. These heat dump/source coils reside about six-feet or more below the ground where temperatures range from 45 to 70 degrees F. year round. Obviously, this has less temperature swing than the outdoor air and because of this the heat pump can obtain heat more readily and can dump to a much cooler material.

In order for a geothermal heat pump to access the ground source, vertical pits or horizontal trenches are required. Inside these trenches, loops are installed in which water or a water/glycol mix circulates. Inside the internal unit of the heat pump resides a heat exchanger where heat moves to or from the refrigerant to the liquid ground loop and transferred to the soil. The soil provides favorable temperatures, and therefore the geothermal heat pump does not need work as hard as air to air units.

Ground source heat pumps can also provide domestic hot water using the same process. Many ground source units are combination and provide many needs beyond space heating, including hot water, heat and cooling and even pool heating.

A water source heat pump uses the same technology as above, only the outdoor liquid loops are installed in vertical wells or in a pond. Instead of using soil as the transfer method these systems use water, which has a reliable temperature depending upon depth.