Thermal response test (TRT) is used to determine the thermal properties of the ground. There is no direct way to measure the ground thermal conductivity and the borehole thermal resistance. These tests are vital for designing ground source heat pump and seasonal thermal energy storage (STES) systems. A TRT is an indirect (in-situ) measurement method which is the simplest and most exact way to determine the effective thermal properties, Gehlin 2002. Thermal Response Tests were first suggested by Mogensen (1983) at an international conference in Stockholm. Mogensen suggested a simple arrangement in which heat at constant power is injected into (or extracted from) a borehole while the borehole mean temperature is measured.
Contents
Equipment
The system consists of a borehole, pipe system, circulation pump, a chiller or heater with constant power rate, and continuous logging of the inlet and outlet temperatures of the flow. The equipment is normally contained within a single unit for ease of transport and efficient use The thermal response data (i.e. temperature development in the borehole at a certain energy injection/extraction) allow estimation of the effective thermal conductivity of the ground and the thermal resistance of the borehole.
Recommendations
In order to fulfil the TRT properly the following recommendations should be taken into account (Gehlin, 2002, Sanner et al., 2005 and Kharseh ):
Preparation
Before the test is started the undisturbed ground temperature must be determined. This can be measured in various ways e.g. by temperature loggings of the borehole or by measuring the temperature of the circulated water through the borehole without heating over 20–30 minutes. The mean fluid temperature corresponds to the undisturbed mean temperature along the borehole. The next step is to switch on the heater and the monitoring system. During the test, the heat transfer into the ground surrounding the borehole is essentially radial and relatively constant along the borehole.
Analysis the Results
Many models are used to analyze the results including that of Kharseh