Knowledge about the effective heat transfer between the transport medium and the sediments in the ground is crucial in the design of a ground source heat pump (GSHP) and borehole thermal energy storage (BTES) system. To this end, a number of thermal characteristics can be measured on site, in particular the thermal conductivity, the thermal resistance of the borehole, the initial average temperature of the ground and the groundwater flow in the drilled formations. These parameters are necessary to correctly estimate the energy transfer within the soil.
In practice, a TRT has 4 phases:
- Installing a borehole heat exchanger to the depth of the final BTES
- Waiting time to give the soil time to thermally equilibrate (about 2 weeks)
- Effective measurement with a measurement setup installed on a trailer
- Reporting the results
A TRT therefore provides detailed data regarding the characteristics of the ground that makes it possible to start the design simulations of the BTES with accurate values. Certainly if it concerns a BTES of a considerable size with at least 10 borehole heat exchangers, it is recommended that the TRT serves as the basis for the design parameters. If a BTES is designed without a TRT, the designer needs to take a sufficiently large safety margin into account. This will result in an overdimensioning of the designed BTES, which will not benefit the return on investment.