Benefits of Geothermal Heat Pump Systems (from US Department of Energy website)

"The biggest benefit of GHPs (Geothermal Heat Pumps) is that they use 25%–50% less electricity than conventional heating or cooling systems. This translates into a GHP using one unit of electricity to move three units of heat from the earth. According to the EPA, geothermal heat pumps can reduce energy consumption—and corresponding emissions—up to 44% compared to air-source heat pumps and up to 72% compared to electric resistance heating with standard air-conditioning equipment. GHPs also improve humidity control by maintaining about 50% relative indoor humidity, making GHPs very effective in humid areas.

Geothermal heat pump systems allow for design flexibility and can be installed in both new and retrofit situations. Because the hardware requires less space than that needed by conventional HVAC systems, the equipment rooms can be greatly scaled down in size, freeing space for productive use. GHP systems also provide excellent "zone" space conditioning, allowing different parts of your home to be heated or cooled to different temperatures.

Because GHP systems have relatively few moving parts, and because those parts are sheltered inside a building, they are durable and highly reliable. The underground piping often carries warranties of 25–50 years, and the heat pumps often last 20 years or more. Since they usually have no outdoor compressors, GHPs are not susceptible to vandalism. On the other hand, the components in the living space are easily accessible, which increases the convenience factor and helps ensure that the upkeep is done on a timely basis.

Because they have no outside condensing units like air conditioners, there's no concern about noise outside the home. A two-speed GHP system is so quiet inside a house that users do not know it is operating: there are no tell-tale blasts of cold or hot air."

Geothermal heat pumps attached to buildings capitalize on the steady temperature of the ground or deep water wells. In effect, they treat the Earth like a giant energy savings bank, depositing or withdrawing heat depending on the time of year. During the summer, the systems pump indoor heat underground and draw on the lower temperatures of the Earth to cool a building. In colder months, the same process works in reverse, with heat from the ground being used to warm indoor air.

Indoors there are box-shaped heat pumps that pull and and push either water or a working fluid, such as antifreeze, in and out of the ground. Using the same compressor loop mechanism that a refrigerator has, a heat exchanger draws energy from the circulating liquid to either heat or cool a building.

There are a number of different configurations for the liquid transfer loops--either water wells several hundred feet deep, which are said to be the most efficient, or coils which could be dug only a few meters underground. Others use a body of water like a pond as a heat sink. Regardless of type, though, ground-source heat pumps are considered one of the most efficient forms of heating and cooling.

The International Ground Source Heat Pump Association, based in Stillwater, Oklahoma, said geothermal is 50 percent to 70 percent more efficient for heating than other systems. The U.S. Department of Energy says that a ground-source heat pump uses 25 percent to 50 percent less electricity than conventional heating and cooling systems. Roberg said that the maintenance costs for geothermal are half the cost of traditional heating and cooling systems. The payback on geothermal systems, which used to be about seven years, is now typically four years, she said. Recently passed federal renewable energy incentives now include $2,000 per year tax credit.

But even with these benefits, geothermal heating and cooling still remains a relatively niche product, with about 50,000 units installed a year in the U.S., according to the Department of Energy. One reason is the upfront cost. All told, a geothermal heating and cooling installation, including duct work, will be about 50 percent more expensive than fossil fuel-based system, Roberg said. Drilling is typically the biggest portion of the bill because it can cost tens of thousands of dollars alone.

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