The response test, also referred to as geothermal response test, is an accepted field method to determine the effective thermal conductance of the ground. The thermal conductance is one of the essential parameters when measuring geothermal probes, energy piles, components with ground contact and geothermal doublet plants (conveyer and injection wells). In-situ measurements of the thermal conductance allow planners to carry out their measurements without safety margins. This enables remarkable savings of investment costs, particularly with medium-size and large geothermal plants. The response test is superior to laboratory measurements as lithologic and ground physical parameters are not corrupted with this methodology. The Senate committee of Berlin demands the execution of response tests with installed capacity of 30 kW and higher.

Sketch – Geothermal response test

Apart from determining the thermal conductance, the so-called thermal borehole resistance can be determined regarding geothermal probes and energy piles. This parameter displays how good the installation of a geothermal probe is or whether the pressing operation material has a high thermal resistance.

In general, a response test is carried out at test bores (extending a test bore with a geothermal probe) or at the first bore of an intended geothermal probe field. With most of the response tests, a constant amount of heat is applied to the subsoil and the temperature response is measured. The failure rate can be reduced to a minimum by using modern SPS-technology which makes the response tests quick, reliable and cost-effective.

The conventional evaluation of a response test is mostly done according to Kelvin’s line source theory [e.g. Hellström, G. (1991-1994), Gehlin, S. (1996-2000)]. The evaluation is based on the mean fluid-temperature-course of the geothermal probe field during the response test.