Closed-Loop Source Heat Exchangers

• November 1, 2018
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Closing the Loop 

Geothermal heat pump systems can be designed using a variety of configurations.  The most common configuration, a closed-loop system, consists of underground, continuous piping loops. These plastic pipes are filled with an anti-freeze-type liquid that helps transfer the ground temperature to the geothermal heat pump. The most common closed-loop systems feature vertical and horizontal ground loops.  

 In urban areas, where space is limited, vertical ground loops can accommodate the installation of geothermal heat pumps. First, boreholes are drilled down into the earth to a depth between 100 and 600 feet, depending on the building’s projected thermal loads. These boreholes vary in diameter between 3⅝” and 6”.  

 Next, two plastic piping lengths are inserted into the borehole with a 180[Symbol] “U”-bend joining the piping at the bottom of the borehole. Center-to-center spacing of boreholes varies, but usually measure 20 feet. Boreholes are grouted from the bottom to the top to provide a mechanical connection between the plastic piping and the surrounding earth, and a seal between aquifers.  

 Borefields can consist of one or two boreholes for residential applications and several thousand for large commercial systems. Since vertical ground loops require minimal space, they are used more frequently than horizontal ground loops. 

 A horizontal ground loop is the next most common installation option for geothermal heat pump systems. A horizontal ground loop field installation typically occurs in rural areas that have a lot of space. These pipes are buried on a horizontal plane approximately six to 10 feet below the ground. In some cases, horizontal ground loop fields can cost less than vertical ground loops because they require no drilling. Horizontal systems can be installed using excavators or other ground moving machines.  

 Staying in the Loop 

 Horizontal systems can also be used in retro-fit situations by utilizing adjacent spaces such as parking lots. In these systems, directionally drilling can expand existing borefields into adjacent spaces without interfering with the existing surface area. 

 Geographic location and available land are two of the most important factors to consider when choosing a geothermal system. Fortunately, technology provides installation options to accommodate any property. The common goal: to provide an ideal, cost-effective living environment while remaining environmentally friendly.