The Ground Response Test - GRT

The Ground Response Test - GRT

The Ground Response Test is a test to verify the response of the ground to a thermal stress. The GRT is carried out on a Borehole Heat Exchanger to determine the thermal properties of the ground:

  • undisturbed ground temperature,
  • ground thermal conductivity,
  • linear global heat exchange coefficient,
  • borehole resistivity.
  • correctly design a geothermal field!

→ the necessary properties to properly design a geothermal system!

Of course, an accurate measurement is a guarantee not only for optimized installation and operating costs, but also for a high system efficiency.

Using the values measured with the GRT it will be possible to simulate the operation of the geothermal system on the long term by means of appropriate FEM software. The simulation is carried out in function of the energy needs of the building and the characteristic parameters of geothermal field (number, depth, type and arrangement of geothermal probes).


The test is performed by imposing a controlled and constantly measured heat flux on the BHE-ground system, by means of an electric resistance. The test is conducted on a pilot BHE that at the end of the test will be part of the expected geothermal field.

The test has a minimum duration of 72 hours, and allows to constantly measure the power exchanged by the BHE with the ground.

Moreover, a first phase of measurement without the use of the electric resistance allows to evaluate the average temperature of the undisturbed ground, thus evaluating the influence of any groundwater.

Having measured the total power supplied to the heat carrier fluid through the electric resistances and the pump, and knowing the input and output temperature of the BHE, the heat transfer coefficient (the thermal conductivity) of the soil (W / mK) can be determined.

After all these data have been collected, the design of the geothermal system can take place.