Geothermal Response Test
The Geothermal Response Test (also termed: Thermal Response Test) is a means of determining the thermal conductivity of the ground and the thermal bore hole resistance (or the thermal conductivity of the bore hole fill).
Knowledge of the thermal properties of the ground is key to the design of geothermal probes. Whereas for small-scale installations the values are usually estimated in accordance with VDI 4640 with appropriate safety tolerances being built into the design, or the design is based entirely on empirical values, larger installations require ground surveys, and where appropriate one or more test bores. Such test bores measure the thermal conductivity of the ground based on two methods:
- Measurement of thermal conductivity from samples which are, as far as possible, undisturbed (such as bore cores). This involves testing all the key rock-specific units of the bore profile and also, especially, determining the natural water content of the samples. (This entails considerable effort and expense.)
- Measurement by a Thermal Response Test (on a fully installed geothermal probe). The advantages of this are that the measurement is taken across the full bore hole length, including the bore hole fill, so providing an indication of the quality of the geothermal probe and the undisturbed ground conditions, including any ground-water flow.
The Thermal Response Test is a tool which optimises and safeguards the design configuration based on direct on-site measurements, even for medium-sized geothermal probe installations.