Sue Butler had had enough of high energy bills. When her old gas furnace went on the fritz, Butler, of Cambridge, Mass., decided to go green -- geothermal green. She began using heat from the Earth to cool and heat her home [source: LaMonica].
How do geothermal systems work? When the seasons change, temperatures fluctuate. But the temperature below the ground stays the same. Only a few feet below the surface, the temperature of the water remains the same, generally around 42 to 80 degrees Fahrenheit (5.56 to 26.67 degrees Celsius) year round, depending on where you live. A geo-exchange system can use this energy to heat and cool almost any kind of building [source: Minnesota Geothermal Solutions].
Geothermal systems do not directly tap into heat inside the Earth. Instead, homes and buildings use geothermal heat pumps to exploit the constant temperature of geothermal wells under the ground. These heat pumps are placed on the inside or outside of a building [source: LaMonica]. The heat pump, which runs on electricity, is a simple device that moves heat from below ground into a home. The heat pump can cool a house in the summer, and warm it during the winter [source: APH Geothermal].
Most geothermal systems are built as closed loop systems. In a closed loop system, a series of underground pipes are filled with a refrigerant, a fluid that absorbs heat from the warm water. When it is cold outside, the fluid absorbs Earth's heat and brings it inside to warm the air. In the summertime, the heat exchange works in reverse, cooling the house [source: LaMonica].
Open loop systems use well or pond water instead of a refrigerant. The heat pump takes the heat out of the water and uses it to warm or cool a house. The water is then pumped back into its original source [source: Alliant Energy].
An electric fan circulates hot and cold air using standard ductwork in both closed-loop and open-loop systems.