Geothermal Heat Pump Systems Part Two – Getting Started With a Formation Thermal Conductivity Test

After reading part one in our series on geothermal heat pump systems, you should be better prepared to decide if this type of system is right for your facility. The next step is to understand how to get started with designing the system. If you determined that a geothermal heat pump system is right for your facility, the very first thing you should do is determine the thermal characteristics of the ground on your site. These characteristics are critical for properly sizing the bore hole field. Under-sizing the bore hole field can result in poor system performance while oversizing the field could cause you to exceed your budget. The only way to accurately determine the specific ground characteristics is to perform a Formation Thermal Conductivity Test (FTCT). During a FTCT, a bore hole is constructed and then tested.

The following are some tips and reminders to help you move forward with your FTCT:

  • If it is not possible to perform the FTCT prior to design completion, then you should require the FTCT as part of the construction contract. If the FTCT is conducted post-design, your mechanical engineer may have to adjust the design based on the FTCT results, which could require change orders.
  • A bore hole FTCT can cost $8,000-$12,000; however, with proper planning, the test bore hole can be incorporated into the final design and about 60-75% of this cost can be applied directly to the construction costs.
  • In order to incorporate the bore hole into the final heat exchanger, you must carefully plan the location of the test bore hole and utilize thermally-enhanced grout similar to what will be used in the final design.
  • A generator is typically used during the FTCT. Keep in mind that the generator will create noise and operate continuously for 48 hours. If you are testing in a residential area, you may want to warn nearby facility owners and residents.
  • The process of creating a bore hole results in the discharge of cuttings, grout and ground water. Make sure to clearly specify, the party who is responsible for sediment control and restoring the site upon completion of work.

Once the FTCT is complete, you are ready to move forward with system design. In part three of our series on geothermal heat pump systems, issued next month, we will identify several different design options for geothermal heat pumps.

In the meantime, if you have any questions about geothermal systems, please contact Michael Rader, PE at or (717) 845-7654.

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