What is a thermal response test?

The design of a ground-coupled heat pump system relies heavily on the thermal properties of the geological materials in which the ground heat exchanger (GHE) is installed.  In the case of a design based on the thermal peaks of a building, it is considered that a 10 % error on the thermal conductivity leads to a sizing error of nearly 10 %. In commercial or institutional projects, this can represent considerable costs.

The thermal properties required for sizing are usually determined by means of a thermal response test (TRT), which consists of dissipating heat in a GHE and measuring its thermal response. Such test is usually carried out with a mobile test unit integrating a water heater, a pump and a few temperature probes.

An attempt is usually made to keep the heating power constant during the test, which allows the TRT to be analyzed with a simplification of the infinite line source model.  Unfortunately, variations in heating power are relatively frequent during a TRT, which does not allow the use of an infinite line source model. The TRT must then be repeated, incurring additional costs.

However, by using advanced interpretation models, it is possible to robustly analyze interrupted, pulsed or oscillating TRTs, or TRTs during which the heating power has varied significantly. In addition to conventional interpretation methods, TRT Analysis has interpretation models for the analysis of complex TRTs.