Heat is extracted from or relinquished to the water, which is then pumped back into the aquifer using a discharge well.
In contrast, open loop systems use a pumping well to extract groundwater from an aquifer that is at a temperature comparable to the mean annual air temperature for the area. Closed loop vertical systems use one or several boreholes with individual loops placed in each these loops circulate a fluid through sealed piping that either absorbs heat from or relinquishes heat to the geologic material surrounding the borehole. Vertical GSHP systems have been installed at depths of up to 400 feet in Indiana. Modeled annual soil temperature variation, Ft.
The efficiency of the system depends on both the temperature gradient surrounding the loop as well as the properties of the geologic materials in which the system is installed.įigure 2. Horizontal systems use closed loops while vertical systems can be either open or closed (fig. The loops can be installed either vertically or horizontally into the earth. GSHP heating and cooling systems use a ground heat exchanger or “ground loop” to move heat from the ground into a building and vice versa.
In other words, these systems are efficient because they do not create thermal energy, but instead move thermal energy between the building and the ground. Still, GSHPs use 25 to 50% less energy than typical heating and cooling systems because energy is being exchanged with the earth instead of relying heavily on electric and fossil fuel energy like traditional systems (USDOE, 2012). Because shallow subsurface ground temperatures show little fluctuation around the average air temperature, heat extracted in the winter months needs to be supplemented to effectively maintain room temperature (70⁰F). It is generally assumed that stable ground temperatures occur at depths greater than 20 feet and mirror average air temperature for a particular location (Hart and Couvillion, 1986). During the winter, heat is pumped from the subsurface into buildings and in the summer, it is transferred from the structure into the ground by reversing the process.Īverage annual air temperatures vary between 47 and 57⁰F in Indiana. Geothermal ground-source heat pump systems (GSHPs) use stable temperatures found in the upper few hundred feet of the earth's surface as a heat battery to efficiently heat and cool homes, schools, and businesses. Indiana Geologic Names Information System Underground Coal Gasification Potential in the Illinois Basin Landmarks in Indiana Geology - A Timeline
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