What is a Geothermal Response Test?
For the planning and performance calculation of shallow geothermal installations - especially for medium to large facilities - accurate knowledge about the thermophysical properties of the underground is a key factor.
The Geothermal Response Test or Thermal Response Test is a widely recognized method for in-situ determination of thermophysical subsurface parameters. Its most important output is the effective thermal conductivity of the prevailing geological layers at the test site.
Furthermore, the mean subsurface temperature (Tu) and the thermal resistance of borehole heat exchangers (Rb) and energy piles (Rp) can be determined. Based on those resistances, inter alia, the material and installation quality of the respective geothermal heat exchangers can be derived.
A response test usually works via a constant heat input into the underground, while its (the underground’s) "temperature response" is measured. The heat input takes place over a period of at least 50 hours. To minimize or eliminate measurement errors, regularly a measurement period of > 72 hours is sought.
The conduction of a GRT/TRT is not limited to borehole heat exchangers and energy piles but is possible with all kinds of closed underground heat exchangers.
The advantage of a GRT when compared to laboratory tests on soil samples is that the measurement is performed at virtually undisturbed subsoil conditions over the entire geothermal heat exchanger length. Therefore, thermal effects of the grout, the technical quality of the geothermal heat exchanger material and installation as well as a possible groundwater flow are included.
If a borehole heat exchanger (BHE) has been installed, it is usable as a part of a BHE-field without restrictions after the end of the GRT.