Efficiency from the earth: geothermal heat pumps; what could be cooler? Architect Laurie Miller gets comfortable with power straight from the Earth's surface.

Are they putting a swimming pool in their front yard?" the neighbors asked about the large rectangular hole next door. No, they're having a geothermal field installed in their front yard. Geothermal heat pumps (GHP) are an energy efficient way to provide heating, cooling, and hot water for residences. Both existing homes and new homes can take advantage of a system that is quiet, durable, low maintenance, comfortable, and can reduce energy bills 40%-70%. HVAC systems use the majority of energy in a home. Geothermal heating and cooling take advantage of the temperature of the earth's surface, which becomes constant just a few feet underground. Ground-source heat pumps use the earth or groundwater as a heat source in winter and a heat sink in summer. Using resource temperatures of 40[degrees]F (4[degrees]C) to 100[degrees]F (38[degrees]C), the heat pump, a device that moves heat from one place to another, transfers heat from the soil to the house in winter and from the house to the soil in summer.

The system requires that piping be installed below the earth's surface. There are two familiar configurations for installation. One is actually a deep well, similar to a well drilled for water and utilizes the same equipment for construction. A geothermal well is practical when there is not a base of solid rock beneath the ground on site, and it is possible to access the area with an auger, or well-drilling equipment. The other type is a shallow field in which copper piping is looped a few feet underground throughout the selected area. The field is often installed in a large rectangular area, thus looking similar to the construction of a swimming pool. This may excite your neighbors!

With the installation of a desuperheater, the GHP can be used to heat the home's water. In summer, hot water is actually a (free) by-product of the cooling cycle of the system. In winter, water-heating costs are reduced by about half.

The cost of a GHP system for a home is about $2,500 per ton of capacity, or $7,500 for a 3-ton unit. A traditional system costs about $4,000. When included in the home mortgage, the system will add a small amount to each mortgage payment. But the energy cost savings will far exceed the amount added to the mortgage. If the project is a retrofit, the system lowers utility bills to the point that the investment pays for itself in two to ten years. Some utility companies offer additional savings to homeowners; so check with your local utilities. The system uses traditional ducting for air delivery, sending clean air, quietly, to all parts of the home. Homeowners enjoy 50% relative humidity and more constant temperatures than traditional systems deliver. According to the U. S. Department of Energy (DOE), in surveys to utilities, more than 95% of all GHP users would recommend the system to their family and friends. According to the Environmental Protection Agency (EPA), GeoExchange systems are the most energy-efficient, environmentally clean, and cost-effective space conditioning systems available (source: "Space Conditioning: The Next Frontier," EPA 430-R-93-004, April 1993). Local geothermal installers will answer questions and provide estimates.

Sustainability goes far beyond the construction of our homes. It becomes part of who we are and affects the way we live our lives. We make choices constantly. Each time we make a purchase, interact with other people, or discard something, we choose whether or not to do so in a sustainable way. Sustainable practices become a habit and enhance life on every level and encourage a rich, diverse culture in which everyone in the community feels that they contribute to the value of society.

Laurie K. Miller, AIA, is an architect living in Asheville, North Carolina and working at Glazer Architecture, PA, 78 Patton Avenue, Asheville 28801. Contact her at 828-254-5853 or [e-mail]

Resources: U.S. Department of Energy (DOE), Office of Geothermal Technologies, EE-12, 1000 Independence Avenue SW, Washington, DC 20585-0121, [phone], http://www.eren.doe.gov/geothermal/