How Do Geothermal Exchange Systems Work?
The planet Earth is the greatest collector of solar energy available, according to the International Ground Source Heat Pump Association. While the temperatures on the surface of the earth vary widely over the course of the year, these changes don't affect much more than the temperature of the surface. The planet itself has been collecting solar energy for billions of years, and such ephemeral changes as seasonal temperature variations are not enough to change the temperature under the surface of the earth. No matter what the season, the temperature six feet below the surface stays relatively constant, between 50 and 70 degrees F. This feature of the earth's temperature is the basis of geothermal heat exchange systems.
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Functions
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A geothermal heat exchange system, also called a geoexchange system and a ground source heat pump system, has two primary functions. In the winter, when the surface temperature is lower than that below the ground, heat from below the ground is drawn up into the house, warming it. In the summer, when the surface temperature is above that below the surface, heat from the house is pumped into the ground, where it disperses, cooling the house. A geothermal heat exchange system functions as both a heater and an air conditioner.
Closed Loop Air System
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One of the three types of geothermal heat exchange systems is the closed loop air system. With this system, a pump sits in the house, drawing air into it and pumping it through a pipe that runs underground. Once in the ground it is warmed and pulled back up into the house, where it is expelled through the vents.
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Closed Loop Water System
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The closed loop water system is much like the closed loop air system, but uses water instead of air. Water has a greater heat capacity than air, and so it can move more heat, making for a more efficient system. The water warmed underground is pumped up into the house where it runs through an extensive series of pipes, which radiate their heat into the house. As the water cools (in winter, or warms in summer) it is sunk back into the earth to be rewarmed. In cold climates, antifreeze is added to the water.
Open Loop Water System
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The third type is the open loop water system. This is only used where there is a continuous source of water available nearby, as from a well or a lake. With an open loop system the water is drawn from the lake or well, pumped underground to be warmed, and then drawn up into the house. Once it cools (or warms, depending on the season) the water is pumped back into the lake, into a well, or allowed to run off over the ground. This type is cheaper and easier to install than the closed loop variety.
Advantages
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Geothermal heat exchange systems can save homeowners from 40 percent to 60 percent off their normal home heating and cooling bills. Because they take advantage of the earth's natural heat store, they burn no fuel for heating or cooling, and so have a much lower environmental footprint.
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