What is “geothermal” heating and cooling, and how is it environmentally friendly?

What is “geothermal” heating and cooling, and how is it environmentally friendly?

—John Moran, Cranston, RI

Geothermal (sometimes called “geoexchange”) heating and cooling is a technology that relies primarily on the Earth’s natural thermal energy, a renewable resource, to heat or cool a house.

In winter or in colder climates, the Earth’s natural heat is collected through a series of pipes, called a loop, installed underground or sometimes in a pond or lake. Water circulating in the loop carries the heat to the home where an indoor system using compressors and heat exchangers concentrates the Earth’s energy and releases it inside the home at a higher temperature. In a typical system, duct fans distribute the heat to various rooms. These systems can also provide all or part of a household’s hot water, according to the Geothermal Heat Pump Consortium, a trade organization.

In summer or in warmer climates, the process is reversed in order to cool the home. Excess heat is drawn from the home, expelled to the loop, and absorbed by the Earth. Thus the system is providing cooling in much the same way that a refrigerator keeps its contents cool—by drawing heat from the interior, not by injecting cold air from the exterior. The only additional energy that these systems need, other than the heat from the Earth’s surface, is a small amount of electricity to power the pumps that circulate the collected heating or cooling throughout the home.

“It’s a truly renewable system requiring a minimal amount of energy,” says Lisa McArthur of the International Ground Source Heat Pump Association, another trade group. “The temperature underground is constant year round (low 40s in the northern U.S. to the low 70s in the South). If a home needs to be heated in the winter or cooled in the summer, the energy source is in one’s own backyard,” she says.

Depending upon the size and quantity of pumps needed, homeowners can expect to pay a few thousand dollars more for installation than for a conventional fossil-fuel system. But with geothermal, homeowners enjoy reduced energy bills, high reliability and long life. “There is always initial sticker shock, but our clientele is more concerned with the environment and long-term use rather than the initial bottom line,” says Scott Jones, a sales manager at ECONAR, a Minnesota-based heat pump producer.

According to the U.S. Department of Energy, geothermal technology can reduce energy costs up to 60 percent compared to traditional furnaces. This means that a geothermal unit will pay for itself in two to 10 years. Subsidies and tax incentives, which vary from state to state, can make the systems even more affordable. Homeowners can check with the free online Database of State Incentives for Renewable Energy to see if their state provides any such incentives.

CONTACTS: Geothermal Heat Pump Consortium, (410) 953-7150, www.geoexchange.org; International Ground Source Heat Pump Association, www.igshpa.okstate.edu; ECONAR, (763) 241-3110, www.econar.com; Database of State Incentives for Renewable Energy (DSIRE), www.dsireusa.org.