Open-Loop Geothermal Water Well Systems

Overview

• While temperatures above the ground vary widely across the United States, temperatures just below the surface of the earth remain between 45 and 75 degrees Fahrenheit year-round, according to the U.S. Department of Energy. Open-loop geothermal systems use a well similar to those used to draw drinking water. They draw water from the well, pass it through a heat exchanger near the home, then use the heat energy extracted from the water to heat the home. The cool water then returns to the underground aquifer through a separate water well, or perhaps even the same well in some cases. Occasionally, the water from an open-loop geothermal system is released to the surface, or to a nearby pond or stream above the ground. In the summer, a reversing valve on the heat pump reverses the process to extract heat from the home using cool underground water supplies.

Pros and Cons

• Unlike traditional heating sources, which burn fuel to generate heat, geothermal systems move and extract existing heat. This allows them to offer efficiency ratings between 300 and 600 percent. Thanks to this high rate of efficiency, many homeowners experience such dramatic reductions in heating and cooling costs that they are able to recoup the cost of these systems in two to 10 years, according to the DOE. Drilling a water well and installing a geothermal heat pump is not a DIY project, and requires a substantial upfront investment. These systems cost significantly more than virtually any other heating and cooling system, which may deter some buyers. Federal and local rebates and incentives may help offset the high initial cost of geothermal heat pumps.

Considerations

• Many cities and states place strict regulations on well systems to avoid potential contamination of underground water supplies, and also to prevent the depletion of aquifers. You also may find strict rules regarding the discharge of the water used in these systems back into the well or to surface sources. While most areas in the U.S. offer suitable conditions for geothermal heat pumps, you should check with a hydrologist and other professionals to make sure this system is appropriate for your home.

Closed-Loop Systems

• When choosing a geothermal system, buyers can select either an open-loop system, which pumps water from a well, or a closed-loop system. Closed-loop systems are much more common, and use a series of sealed pipes filled with antifreeze or some other heat transfer liquid. Installers drill holes for these pipes, which absorb or release heat energy as they pass through the earth. The antifreeze in the pipes then travels through a heat exchanger to heat or cool the home. While open-loop systems generally are cheaper to install, and take advantage of natural water supplies for heating and cooling, they may not be practical for all applications because of the large water supply required for operation. Mother Earth Living reports that closed systems are more appropriate and cost effective for most residences because they require less space and do not require a substantial water supply.