Geothermal Heat Pumps

Geothermal heat pump systems (also known as geoexchange, ground or water-source heat pumps, earth energy, and earth-coupled) use geothermal energy to provide central heating, air conditioning, and hot water to a home. They use the ground under the earth’s surface as either a source of heat or as a coolant to adjust the temperature of air and water in both commercial and residential properties. These heat pumps use the heat from only a few feet under the earth’s surface, unlike deep geothermal energy, which is harvested 2-10 Km into the earth.¹·²·³·⁴

How It Works

While the outdoor temperature changes from very warm to very cold throughout the year in most places, the temperature below the earth’s surface remains fairly constant in the temperature range of 45ºF-75ºF.¹·² Geothermal heat pumps (GHP) use this steady temperature by drawing heat out from the earth into the home during the winter, and taking heat out of a home and into the earth in the summer.

Geothemral Heat Pump http://www.gregfiore.com/Opinions/Geo%20Thermal/heat_transfer.jpg
Geothemral Heat Pump http://www.gregfiore.com/Opinions/Geo%20Thermal/heat_transfer.jpg

During the winter the heat is collected by a fluid-filled series of pipes that run under ground or submersed in a lake. The warmed fluid is carried back into the home and then the GHP system uses an electrically powered compressors and heat exchangers in a vapor compression cycle to concentrate the energy and release it inside the home at a higher temperature. In most systems, duct fans distribute the heat to various rooms. Some GHP models are even available with two-speed compressors and variable fans which provides the user with more heating options, as well as energy savings.¹·²

In the summer, the GHP system acts as a refrigerator. Instead of blowing cold air into the home, it draws heat out of the home and expelled through the ground loop to be absorbed by the earth.ii Unlike most air condition systems which have outdoor compressors, GHP compressors and all components can be installed inside the home, which prevents damage from the elements.¹·²


Some GHP systems are also equipped to provide all or at least part of a home’s hot water. The same process of drawing the heat from the earth is used in this process; extra equipment is just needed to transfer the energy to the water to heat it.²


Types of Loops

Loops for residential GHP systems are installed either horizontally or vertically in the ground or submersed in apond or lake. Most systems used a closed-loop series of pipes, but there are also open-loop systems where two unconnected pipe lines are used to collect and discharge water. ¹

Vertical Closed Loop
These GHP systems use the natural thermal properties of the earth in a similar way to the Ground Water Energy systems. The difference is the GHP systems circulate water or antifreeze in their closed vertical network of plastic pipes instead of pumping water out of a well and then back into the ground. These vertical wells are drilled to a depth of 100 to 300 feet per ton of air conditioning. The vertical closed loop series is ideally suited for homes with limited land area.
Different Types of Closed Loop GHPs http://www.engineer.gvsu.edu/house/images/additional/heatpump.jpg
Different Types of Closed Loop GHPs http://www.engineer.gvsu.edu/house/images/additional/heatpump.jpg

Horizontal Closed Loop
Much like the vertical closed loop series, the horizontal closed loop system also uses the thermal properties of the earth by circulating water or antifreeze through a closed loop network of sealed and pressurized plastic pipe that is buried in the ground. However, instead of installing the plastic pipe vertically the pipe is laid into horizontal trenches typically 4 to 6 feet deep with a length of 75 to 400 feet per ton of air conditioning. Piping can also be coiled to help increase the amount of piping in a given area; this is called a slinky loop. While these systems to require more land area, the cost is much lower than the vertical closed loop system.⁵

Pond or Lake Submersion
If a residence has a large enough body of water the water submersion of the closed loop series is the most cost efficient GHP system. A water or (more likely) antifreeze filled pipe is run underground from the home to the water and is coiled into circles and placed at least eight feet under the surface of the water to prevent freezing.⁶
groundloop.jpg
Open Loop GH http://www.capitalwell.ca/Geo_Thermal.htm

Open Loop
These systems use well or surface body water as the heat exchange fluid instead of fluid filled sealed pipes. Once collected water circulates through the system, the water returns to the ground through a recharge well or surface discharge. Open loop systems can only be used where there is a large enough supply of relatively clean water.⁶

Benefits of GHP Systems

Cost Savings
While the intial installation of GHP systems can range from $15,000-$20,000, the systems save enough energy to pay for themselves in 5-10 years.¹·³·⁴ Also, because the components are kept indoors they are much less likely to get damaged. The components have an estimated lifetime of 25 years and the loops have an estimated life of 50 years.¹·²

Energy Savings & Cleaner Energy

The EPA’s Green Power Partnership includes geothermal energy as a clean, renewable energy source (or "Green Power"). One of the biggest benefits of GHP systems is that they use 25%–50% less electricity than conventional heating or cooling systems. According to the EPA, geothermal heat pumps can reduce energy consumption, and thus the emissions from standard energy consumption, up to 44% compared to air-source heat pumps and up to 72% compared to electric resistance heating with standard air-conditioning equipment.¹·⁸ GHP systems also have no air emissions other than what is produced from the electricity that powers the compressor, losses only small amounts of water to evaporation, and has a low risk of ground water contamination (especially with closed loop systems). This lower amount of emissions will help reduce the CO2 output of homes, and possibly halt the temperature increases from global warming.⁹

This clean source of energy is becoming more and more popular among residental homes; especially to those trying to have more green buildings and attain LEED certification.
¹⁰


1 U.S Department of Energy, "A Consumer's Guide to Energy Efficiency and Renewable Energy - Geothermal Heat Pumps." http://apps1.eere.energy.gov/consumer/your_home/space_heating_cooling/index.cfm/mytopic=12640 (April 1, 2009)
2 Geothermal Heat Pump Consortium, "What is GeoExchange?" http://www.geoexchange.org/geothermal/geoexchange-explained/what-is-geoexchange.html (April I, 2009)
3 Alexander, Maxwell,"Geothermal Heat Pump: How It Works." This Old House Magazine.http://www.thisoldhouse.com/toh/article/0,,20162296,00.html (April 1, 2009)
4 Consumer Energy Center, "Geothermal or Ground Source Heat Pumps." http://www.consumerenergycenter.org/home/heating_cooling/geothermal.html (April 1, 2009)
5 Capital Well Drillers,"Geo Thermal." http://www.capitalwell.ca/Geo_Thermal.htm (April 1, 2009)
6 U.S Department of Energy,"A Consumer's Guide to Energy Efficiency and Renewable Energy - Types of Geothermal Heat Pump Systems." http://apps1.eere.energy.gov/consumer/your_home/space_heating_cooling/index.cfm/mytopic=12650 (April 1, 2009)
7 Environmental Protection Agency,"Green Power Partnership Brochure 2008." 2008. http://www.epa.gov/greenpower/documents/GPPbrochure08.pdf (April 1, 2009)
8 Health Goods, "Geothermal Heat Pumps Make Sense For Homeowners." http://www.healthgoods.com/Education/Healthy_Home_Information/Space_Heating_and_Cooling/geothermal_for_homeowners.htm (April 1, 2009)
9 Environmental Protection Agency,"Non-Hydroelectric Renewable Energy." http://www.epa.gov/cleanenergy/energy-and-you/affect/non-hydro.html#geothermal (April 1, 2009)
10 McQuay Air Conditioning, "Optimizing Geothermal Heat Pump Systems For Higher Efficiency, Maximum LEED Points and Lower Installed Costs." Engineering System Solutions, April 2005. http://www.mcquay.com/mcquaybiz/literature/lit_systems/EngNews/0405.pdf (April 1, 2009)