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| Fig. 1: This figure shows the steps for a ground source heating pump in a vertical closed loop geothermal heating system (Source: Wikimedia Commons) |
Geothermal heat pumps are a clean and efficient renewable energy technology that can be used to heat a home. A geothermal heat pump is an electrically powered unit that transfers energy to and from the earth. [1] They use the constant temperature of the earth as the exchange medium, instead of outside air. [1] Although many parts of the country experience seasonal temperature changes and exchanges, the temperature of the ground is relatively constant just a few feet below the earth's surface. [1]
There are four different types of geothermal heat pump systems, and three of the four are closed loop systems. All four can be used for homes, choosing the best system depends on climate, soil conditions, and available land. [2] Geothermal heat pumps are particular a good option to more efficiently heat your home if you are building a new home or planning major renovation of an existing home. [1]
Closed loop geothermal heat pump systems circulate an antifreeze solution through a closed loop (usually made of plastic) that is buried underground. Then a heat exchanger transfers heat between the refrigerant in the heat pump and the antifreeze solution in the closed loop. [2] A horizontal closed loop system is generally the most cost effective for home installations, but there needs to be a larger amount of available land compared to other systems. [2] The pipes are then buried in the ground in a set trenches that must be at least 4 feet deep. Pipes can then be looped around to allow more pipe in a shorter trench. [2] Vertical loops can be used where the soil is too shallow for trenching, and they minimize the disturbance to the existing landscape. [2] The pipes are connected in a U bend form in holes that are drilled into the ground 20 feet apart and 100 feet deep. [3] If a home is close to a body of water then the pond/lake geothermal system could be the best option. A pipe is run underground from the building to the body of water and coiled into circles at least eight feet under the surface, however the water source has to meet a number of depth, volume, and quality requirements. [2] Finally, open looped systems use a well as the heat exchange fluid that circulates directly through the geothermal heating system. [2]
All of the closed loop systems utilize a ground source heating pump, where a heat pump takes heat from the ground and delivers it to a home. There are four main steps to this process: circulation, heat absorption, heat exchange, and recirculation. First, during the circulation step the above ground heat pump moves water (or another fluid) through the series of buried ground loop pipes. [3] Next, as the fluid passes through the ground loop, it absorbs heat from the warmer soil around it. [3] The heated fluid then returns to the building where it can be transferred into the homes air distribution system to heat the home. [3] Once the fluid transfers its heat to the building, it returns to a lower temperature to be heated again. Fig. 1 shows these steps for a vertical closed loop system.
Geothermal heat pumps are a great option for efficiently heating a home. High- efficiency geothermal pumps are on average 40-60% more efficient than convention gas and electric furnaces. [2] Due to the energy efficient, clean technology, geothermal heat pumps are gaining popularity for home heating.
© Maeve White. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] "Guide to Geothermal Heat Pumps," US Department of Energy, DOE/EE-0385, February 2011.
[2] "Geothermal Heat Pumps," U.S. Office of Energy Efficiency and Renewable Energy, DOE/GO-11098-652 FS 105, September 1998.
[3] B. Matek et al., "Using Geothermal Energy and Industrial Waste Heat for Power Generation," Geothermal Energy Association, December 2015.
