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What is Geothermal Heating & Cooling?

Geothermal systems can save 25 to 40 percent of the heating and cooling costs over conventional systems. Although the installation costs for geothermal systems can be higher than for less-efficient systems, substantially lower utility bills rapidly offset the initial cost.
Beneath the frost line, the ground stays a constant temperature of about 60 degrees Fahrenheit. That happens to be an extremely efficient operating temperature for heat pumps. Geothermal heat pump systems circulate water between an underground water loop, called an earth heat exchanger, and water-to-air heat pumps located throughout a large building.

The earth heat exchanger is most often a network of high-density polyethylene (HDPE) piping buried in vertical boreholes (wells) 150 to 300 feet deep. Each of the heat pumps in the building is connected to the circulating water loop. The temperature is controlled independently at the individual heat pumps located in rooms throughout the building. The constant temperature of the earth heats or cools the circulating water loop as needed to balance the building?s year-round heating-and-cooling requirements.

Thermal Conductivity Testing

Ground testing provides the geothermal system designer accurate information on the thermal conductivity and thermal diffusivity of the geologic formation in which the boreholes and ground loops will be installed. An optimized system will save money by reducing the length of piping required. Without accurate data, systems are often conservatively over designed. Drilling test bores ensures that your site is suitable for geothermal-loop field piping. Soil thermal-conductivity testing assesses the capacity of the ground at your site to transfer energy to and from the geothermal-loop field piping. Once the borehole is drilled, the loop installed, and the borehole is grouted, a thermal conductivity test is conducted.

Hot water from a portable electric heater is circulated through the loop. A data log of incoming and outgoing water temperature is run for a 44 to 48 hour period. These data are then analyzed using the ?line source? method. The average temperature of the water entering and exiting from the u-bend loop heat exchanger is plotted versus the natural log of time. Using the Method of Least Squares, the linear equation coefficients are calculated to produce a line that fits the data.

Parameters calculated include the Formation Thermal Conductivity (Btu/hr-ft-degree F), the Formation Thermal Diffusivity (Ft.sq./day), and Undisturbed Formation Temperature (degrees F). The design engineer uses these values in commercially available software programs such as GchpCalc (available at to optimize the loop system by using the minimum number of boreholes and shortest loop lengths.

Bradfield Environmental Services, Inc. can provide and install test borehole(s) and conduct thermal conductivity tests. Thermal conductivity tests include installation of all testing equipment, providing generator power, and delivery of a final report with design parameters needed to fully optimize your geothermal project. We can also design your geothermal system from start to finish. Call today for a free consultation.

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