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Geothermal Energy: Drilling Beneath the Surface of Our Energy Dilemma
(Released September 2009)

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  by Ethan Goffman  


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Geothermal Heat Pumps


Geothermal heat pumps (GHPs), a technology already developed and widely available across the United States, have the potential to become predominant in home heating and cooling. Rather than tapping into the earth's interior, GHPs rely on the fact "that the ground absorbs 47 percent of the sun's energy that reaches Earth . . . 500 times more than humankind needs every year" (Whittington). Like conventional heating and air conditioning, GHPs pump heat out of a house or building in hot months and draw heat in during cold months. For conventional systems, this requires hard work, and therefore uses a lot of electricity. Conventional technology battles natural cycles, pumping heat outside on already hot days, or fighting exterior cold. GHPs, by contrast, draw from the steady temperature about 10 feet (3 meters) below the earth, a little above 50° F (10 ° C). GHPs therefore require far less energy. And GHPs are liquid based, another advantage over conventional systems that do the difficult work of extracting heat from air (Sunteq). The energy for GHPs exists virtually anywhere on earth, even in cold climates; the technology has been used in Alaska, Canada and Greenland (Whittington).

A GHP is a heat pump that moves heat into or out of a home depending on need. There are two basic GHP systems: closed loop and open loop. Open loop connects to an exterior source, such as a lake or well, taking advantage of its natural properties, efficiently transferring "energy to and from a steady stream of subterranean water" (Air Conditioning). Of course such a source is often unavailable, necessitating the use of closed loop systems, which recycle a liquid, often a refrigerant, into the earth and back. Closed loop are either horizontal, where land is available, or vertical, which saves space but costs more. Where space is limited, vertical loops can be used, although these require drilling wells, generally between 300 and 1,800 feet deep (91 and 550 meters) (Sanford).

types of GHPs
Geothermal Heat Pumps

Unlike large geothermal installations, GHPs do not actually produce electricity, but require an external source. Still they are far more efficient than conventional units, since "electricity is required to run the equipment, but no fuel is burned to create the heat" (Sanford). GHPs therefore shave 30 to 60% off the cost of "traditional heating and cooling systems, because the electricity which powers them is used only to collect, concentrate, and deliver heat, not to produce it" (Geothermal 101). Another study estimates that GHPs could reduce the growth in nonrenewable energy use in buildings by 35 to 40% (Hughes).

Even more benefits can be eked out of GHPs. Because "the byproduct of cooling from a geothermal system is heating" (Hayden), GHPs can be used to heat water via waste heat from air conditioning through a piece of technology known as a desuperheater. However GHP water heating can only supplement an existing system; it will not work year-round.

GHPs do share one huge drawback with geothermal electricity generation: initial cost. In general, a "home of about 2,000 square feet would require about a three-ton system. On average, a GHP system costs about $2,500 per ton of capacity, or roughly $7,500 for a three-ton unit" (Calahan). A similar conventional system would cost only about $4,000 (Calahan). Added to this for GHPs is the cost of drilling, which runs from $10,000 to $30,000 (California Energy). Still, a geothermal system saves about $1,000 annually (Rupar) and payback time ranges from five to twelve years (Kozlowski). GHPs are also easier to build into new construction than to retrofit. GHPs are especially useful for larger homes, complexes, and buildings, for which they have a much shorter payback time. Schools have often chosen GHPs, "as school planners think beyond first costs and look at operating costs" (Hayden). Furthermore, given that the basic knowledge and infrastructure for GHPs is sparse, as they become more widespread installation costs will undoubtedly come down.

Another long-term benefit of GHPs, which may be overlooked, is longevity. GHPs last 25 to 30 years, twice as long as air source heat pumps (Vastyan). Of course the benefits of using a clean air source are not reaped by the individual user, but by the wider society and the planet. Using less power means that "installing a geoexchange system in a single-family home is equal in greenhouse gas reduction to planting an acre of trees or taking two cars off the road" (Sanford). Other environmental benefits include less local pollution and less harm from mining, for instance where coal is the source of electricity.

Already, the United States has over 600,000 GHP units (Hughes). Still, Europe is currently installing two to three times as many unitsas the U.S., where GHPs are often overlooked. A U.S. Department of Energy report "recommends that federal policymakers seriously consider aggressive nationwide deployment of GHPs, with programs commencing as soon as possible" (Hughes).

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Special thanks to the Geothermal Energy Association for their help with this Discovery Guide

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