Geothermal Heat Pumps

These geothermal heating and cooling units installed in the basement of a new home are tied to a complex array of underground coils to keep indoor temperatures comfortable. | Photo courtesy of ©iStockphoto/BanksPhotos

When selecting and installing a geothermal heat pump, consider the heating and cooling efficiency, the economics of the system, and your site's characteristics. Be sure to find a qualified installer.

Heating and Cooling Efficiency of Geothermal Heat Pumps

The heating efficiency of ground-source and water-source heat pumps is indicated by their coefficient of performance (COP), which is the ratio of heat provided in Btu per Btu of energy input. Their cooling efficiency is indicated by the Energy Efficiency Ratio (EER), which is the ratio of the heat removed (in Btu per hour) to the electricity required (in watts) to run the unit.

Look for the ENERGY STAR® label, which indicates that the unit meets ENERGY STAR criteria. Manufacturers of high-efficiency geothermal heat pumps (GHPs) voluntarily use the EPA ENERGY STAR label on qualifying equipment and related product literature. Many GHPs carry the U.S. Department of Energy (DOE) and Environmental Protection Agency (EPA) ENERGY STAR label.

Economics of Geothermal Heat Pumps

Although the purchase and installation cost of a residential GHP system is often higher than that of other heating and cooling systems, properly sized and installed GHPs deliver more energy per unit consumed than conventional systems. For further savings, GHPs equipped with a device called a "desuperheater" can heat household water. In the summer cooling period, the heat that is taken from the house is used to heat the water for free. In the winter, water heating costs are reduced by about half.

Depending on factors such as climate, soil conditions, the system features you choose, and available financing and incentives, you may recoup your initial investment in two to ten years through lower utility bills. And -- when included in a mortgage -- your investment in a GHP will produce a positive cash flow from the beginning. For example, if the extra $3,500 cost of the GHP will add $30 per month to each mortgage payment, the energy cost savings will easily exceed that added mortgage amount over the course of each year.

On a retrofit, the GHP's high efficiency typically means much lower utility bills, allowing the investment to be recouped in two to ten years. It may also be possible to include the purchase of a GHP system in an "energy-efficient mortgage" that would cover this and other energy-saving improvements to the home. Banks and mortgage companies can provide more information on these loans.

There are also special financing and incentives available to help offset the cost of adding a GHP to your home. These provisions are available from federal, state, and local governments; power providers; and banks or mortgage companies that offer energy-efficient mortgage loans for energy-saving home improvements. Be sure the system you're interested in qualifies for available incentives before you make your final purchase.

Evaluating Your Site for a Geothermal Heat Pump

Shallow ground temperatures are relatively constant throughout the United States, so geothermal heat pumps (GHPs) can be effectively used almost anywhere. However, the specific geological, hydrological, and spatial characteristics of your land will help your local system supplier/installer determine the best type of ground loop for your site.

Geology

Factors such as the composition and properties of your soil and rock (which can affect heat transfer rates) require consideration when designing a ground loop. For example, soil with good heat transfer properties requires less piping to gather a certain amount of heat than soil with poor heat transfer properties. The amount of soil available contributes to system design as well -- system suppliers in areas with extensive hard rock or soil too shallow to trench may install vertical ground loops instead of horizontal loops.

Hydrology

Ground or surface water availability also plays a part in deciding what type of ground loop to use. Depending on factors such as depth, volume, and water quality, bodies of surface water can be used as a source of water for an open-loop system, or as a repository for coils of piping in a closed-loop system. Ground water can also be used as a source for open-loop systems, provided the water quality is suitable and all ground water discharge regulations are met.

Before you purchase an open-loop system, be sure your system supplier/installer has fully investigated your site's hydrology, so you can avoid potential problems such as aquifer depletion and groundwater contamination. Antifreeze fluids circulated through closed-loop systems generally pose little to no environmental hazard.

Land Availability