The most important element of the primary circle of borehole heat exchanger (BHE) system is to define the necessary length, number and distance of the boreholes.
Thus, the BHE field can be optimized by conducting this response test and so the installation and operation of the subsequent heat pump system will not only be cost efficient but also reliable in the long run.
The Geothermal Response Test process:
1. drilling of test-borehole and then geophysical logging in it
2. installation of test-BHE pipe
3. BHE grouting (the completion of the borehole heat exchanger is done according to the VDI 4640 guideline)
4. filling the pipe with working fluid
5. Ground-state temperature recording
6. Assembly and commissioning of the testing appliance
7. Borehole airing
8. Starting the test with a minimum duration of 48-72 hours
9. Disassembly of the testing appliance
10. Temperature recovery measuring in the whole BHE length 4 times: immediately after measurement, respectively 1, 2 and 3 hours after the test
11. Determination of the results:
a. Definition of the borehole thermal resistance (Rb) and the ground thermal conductivity (λ)
b. Interpretation of the run of the temperature log
The obtained data from Thermal Response Test are evaluated based on two methods in favour of reliable results: the geological thermal conductivity can be determined with the purpose-developed German GeoLogik TRT Analysis Software and even with the traditional analytical method.
Modelling can be performed by EED (Earth Energy Designer) Program following the evaluation of the geothermal response test results; the adoption of this program is general in Europe in case of similar projects. Application of the program enables determination of the length of geothermal heat exchanger, the difference between boreholes, the borehole depth and arrangement as well as the temperature of the heat carrying agent circulated in the geothermal heat exchanger, and, fitting them to each other. In addition to basic dimensioning, the calculation of the necessary borehole length is also possible on basis of data input, it means to optimize the response test system.