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Heat from the Underground

A new twist on an old favorite-the heat pump-is gaining ground in the green building movement. Geothermal heat pumps (GHPs) use natural thermal energy stored just below the earth's surface to provide space heating during the winter and cooling in the summer. They also can be configured for radiant heat and domestic water heating.

Just a few feet underground, the temperature remains at a relatively constant 50 to 60 degrees Fahrenheit year-round. Animals take advantage of this warmth by burrowing into the ground to hibernate. Similarly, geothermal heating systems employ buried pipes to access the earth's warmth for indoor heating.

Geothermal systems do not burn fossil fuels to create heat. They cost very little to maintain and operate, and they provide homeowners with an affordable alternative to rising fuel prices-although they are significantly more expensive in first cost.

A Dream Home
When John and Linda Cavanagh built their dream home in Rye, N.H., in 1992, they wanted to avoid using oil or natural gas. They installed a geothermal heat pump system, but not without careful thought. John was a little apprehensive about being a pioneer in geothermal technology.

"Geothermal was somewhat of a leap of faith in technology because the traditional heating system up here is fossil fuel," says John. "When it's not something your neighbor has, you greet it with a bit of skepticism. That's the New England way."

Today, though, he's happy with his choice-a direct-exchange (DX) geothermal heat pump from ECR Technologies, Inc. A "desuperheater" takes the heat collected during the air-conditioning cycle and transfers it to the home's hot water storage tank for supplemental water heating in the summer. The result is substantially lower water-heating bills for Linda and John, as the system saves energy normally used by the hot water heater.

Direct and Efficient
DX geothermal systems offer a number of advantages over standard water-based geothermal heat pumps, according to Joe Parsons, director of marketing for ECR Technologies. The key difference is that copper is used for the underground heat-exchange process, which involves only one heat transfer process. Water-based geothermal systems typically rely on plastic for underground piping, which requires two heat exchanges. As a result, the system uses about twice the energy as a DX geothermal system, says Parsons.

Greater thermal conductivity, flexibility and availability in small diameters make annealed or "soft" copper tubing ideal for the long underground tubing runs required in DX geothermal heating/cooling systems, says Andy G. Kireta Jr., national program manager of building and construction, Copper Development Association. "Heating and cooling are the biggest energy-users in the home," he says.

Energy Savings
In the past 12 months, the Cavanaghs estimate they have spent a total of $972 or 38 cents per square foot for heating, cooling and hot water for their 2,600 sq. ft. home. If oil had been their primary fuel source, their annual heating costs alone would have exceeded $2,000, according to ECR calculations.

The system cost about $9,000 including installation, which required drilling four bore holes about 100 feet into the ground. However, the Cavanaghs received $8,000 in energy rebates for building their house to Energy Star specifications set by the U.S. Environmental Protection Agency. (Other energy-efficient features used in the home's construction include structural insulated panels, energy efficient windows and compact fluorescent lighting.)

"DX geothermal gives homeowners a way to reduce their energy bills, while helping promote a healthier environment," notes CDA's Andy Kireta. "That's technology all of us can live with."

For more information on DX geothermal technology, visit the Copper Development Association's Web site at www.copper.org.

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