GEOTHERMAL HEAT PUMP BASICS

Geothermal Heating and Cooling 101
Susan DeFreitas, October 20, 2010 (Earth Techling via Reuters)

"…[G]eothermal heat pump installations have seen strong growth over the past 6 years, and, as of 2008, totaled over 1 million nationwide. Approximately 100,000 to 120,000 systems are installed annually in the U.S. in about 1 out of every 38 new U.S. homes…While the popularity of geothermal heating and cooling may be new, the technology itself has been around since the late 1940's. Geothermal heat pumps work by exploiting a natural fact: no matter how large the atmospheric temperature fluctuations in different regions of the world, the temperature just a few feet below the earth's surface remains a steady 45 degrees F (7 Celsius) to 75 degrees F (21 Celsius)…

"The parts of a geothermal heat and cooling system include a heat pump, an air delivery system (i.e., ductwork), and a heat exchanger. The heat exchanger is, essentially, a system of pipes buried in shallow ground. In the winter, when above-ground temperatures drop, the heat pump removes heat from the below-ground air inside the heat exchanger and pumps it into the building via the indoor air delivery system. In the summer, the process is reversed, and the heat pump pulls air from inside the building into the heat exchanger, where heat is removed, thanks to cooler temperatures below-ground. As an added bonus, heat removed from the indoor air during the summer can also be used to provide a free source of hot water…"

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"Geothermal systems come in four types, each of which are appropriate for different circumstances, based on the climate, soil conditions, available land, and local installation costs. All four approaches are equally appropriate for residential and commercial applications…

"...[1] The Horizontal type system is generally most cost-effective for residential installations…[2] The Vertical system, as the name suggests, requires less in the way of acreage and more in terms of trench depth, and is often more appropriate for large commercial buildings…[3] [A]Pond or Lake system, makes use of an existing body of water and a water-source heat pump…[4] [T]he Open Loop system, uses well or surface body water as the heat exchange fluid…"

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"While there are no areas where geothermal heat pumps won't work at all, there are places where efficiencies and installation costs make them impractical-for instance, areas with very dry soils, or where the climate is relatively mild and varying, such as coastal California. In the latter type of settings, an air source heat pump (which operates the same way as a ground source heat pump, but without taking air from below the ground) will do just as well…

"[T]he federal government will kick in a 30 percent federal tax credit as part of a credit that also applies to solar technology. A wide variety of state and local incentives are also available…[More acceptance] rests largely in the costs of adoption and individual contractors' willingness to learn a new technology…"