Geothermal System Types
Geothermal ground loops can be installed in a variety of ways, depending on the region, climate, cooling/heating requirement, excavation costs and soil conditions. The three most popular loop configurations are vertical, horizontal and pond loop.
Vertical Closed Loop
Both vertical and horizontal loops extract the Earth’s natural heat and reject it back. Vertical loops (shown) are installed by drilling vertical bore holes several hundred feet into the earth and inserting a plastic polyethylene supply/ return pipe into the holes. At these depths, the undisturbed ground temperature does not change throughout the year. Vertical loops only require approximately 250 to 300 ft² of surface area per ton of cooling.
Horizontal Closed Loop
Horizontal loops extract the Earth’s natural heat and reject it back. Horizontal loops are installed in trenches approximately 5 feet below the ground surface. The undisturbed ground temperature often changes seasonally depending upon where the loops are installed. Horizontal loops are easier to install, but require significantly more area (approximately 2500 ft²/ of surface area per ton of cooling).
Surface Water or Lake Loop
A "Surface Water" or "Lake" closed loop system is a geothermal loop that is directly installed in a lake or body of water that is near the building. In many cases, the body of water is constructed on the building site to meet run-off or aesthetic requirements. The size and the depth of the lake is critical, and commercial design services should be used to certify that a given body of water is sufficient to withstand the building loads.
Open Loop "Well Water"
"Open Loop" well water systems use ground water to remove or add heat to the interior water loop. The key benefit of an open loop system is the constant water temperature, usually 50°F to 60°F, which provides efficient operation at a low first cost. Open Loop applications are commonly used in coastal areas where soil characteristics allow reinjection wells to return the water back to the aquifer. Reinjection wells must be approved by the U. S. Environmental Protection Agency and local building codes.