Geothermal Power: Heating and Cooling the Home

Introducing the most efficient, cost-effective way to heat and cool your home: geothermal power, by transferring and storing heat from the earth, with a geoexchange system.

| April/May 2001

Exchanging Heat With the Planet

One of the most frequent comments we hear from our customers who have switched from conventional heating systems to geothermal is that the system's so quiet they cannot tell if it's operating. Many customers tell me they feel the need to check the thermostat and system in the basement to be certain that everything is still working. (Another thing they often say is, "we only wish we had decided to switch to geothermal long ago.")

Since soil temperatures several feet below the surface remain at a nearly constant 50°F year round, the earth actually acts as a massive low temperature solar storage unit — cooler than surface temperatures in the summer, warmer than the surface in the winter. Geothermal energy, also known as geoexchange, is literally the transfer and storage of heat from the earth.

Similar to your kitchen refrigerator, a residential geoexchange system uses water or a nontoxic refrigerant that circulates through a ground loop where it absorbs heat. A compressor then amplifies this heat to a higher useful temperature before rejecting the heat through a finned heat-exchange coil into the household duct system. This system also allows the cooled refrigerant to flow into an expansion valve so that a "reversing valve" can automatically change the direction of refrigerant flow to provide air conditioning. Many residential systems also incorporate a small auxiliary heat exchanger called a desuperheater to heat the domestic water supply, providing 60% of the normal household hotwater load. In the summer, the hot water is a byproduct of air conditioning and in winter, hot water is made at one-third the cost of operating an electric hot water tank.

While a geoexchange system will not relieve you completely of dependence on grid power, it will dramatically reduce the amount of electricity you need from your local utility without sacrificing comfort. Indeed, this type of system can provide heat up to 100°F and air conditioning down to 45°F. In summer months, if the compressor in your basement has to work only to reject heat to the cool earth rather than the much hotter outdoor temperatures, it can provide two to three times as many cooling BTUs per watt of power consumed. That equals a savings of 50% to 66% in cooling cost and a dramatically reduced electrical load for the utility.

Moreover, since the Earth provides 75% of the heating and cooling energy, analysts are discovering that noise and thermal pollution from outdoor units is minimal. Electrical generation, transmission loads and power plant emissions can be reduced by 400% per household. All around, geothermal energy is a win-win option for the environment, utility companies and the homeowners.

The Birth of Geothermal

The idea for geothermal heating and cooling dates back to the early 1940's when water-cooled heat pumps and air conditioners first evolved. Engineers and technicians realized that water had a high rate of heat transfer that allowed for smaller heat exchangers and minimal refrigerant charges. From the 1940's to the 1970s, however, energy was cheap, and not everyone had access to large volumes of clean water or a place to discharge it. Consequently, most of the early watercooled systems were used in commercial structures where well water or process water was in continually available. Meanwhile, the notably less efficient air-source systems enjoyed a major market growth due to their ease of installation.

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