Geothermal Energy Sources

Geothermal units use the constant temperature of the earth as the exchange medium instead of the outside air temperature. This allows the system to reach fairly high efficiencies on the coldest of winter nights. While many parts of the country experience seasonal temperature extremes – from scorching heat in the summer to sub-zero cold in the winter – a few feet below the earth's surface the ground remains at a relatively constant temperature. Ground temperatures range from 45°F to 75°F. Like a cave, this ground temperature is warmer than the air above it during the winter and cooler than the air in the summer. The geothermal units take advantage of this by exchanging heat with the earth through a ground heat exchanger.

Closed-loop systems circulate a water-based solution through a "loop system " of small-diameter, high-density polythylene underground pipes. Closed-loop systems can be installed horizontally, vertically or in a pond. Open-loop systems use an existing water well or surface water. Whether the system is open or closed, heat is transferred to or from the structure, regardless of outdoor temperature, to provide year-round comfort.

Horizontal Loops:

Often used when adequate land surface is available. Depending on geothermal system needs and space available, pipes are placed in trenches that range in length from 100 to 400 feet.

Vertical Loops:

The ideal choice for a geothermal heat pump when available land surface is limited. Well drilling equipment is used to bore small-diameter holes from 100 to 400 feet deep.

Pond (Lake) Loops:

Very economical to install when a large body of water is available for use by the geothermal heating and cooling system. Coils of pipe are simply placed on the bottom of the pond or lake to capture the geothermal energy.

Open loops (Well-Water Systems)

In ideal conditions, an open-loop application can be the most economical type of geothermal system. These use groundwater from a well as a direct energy source.

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