Thermal Response Test

Thermal Response Test (Termisk Responstest in Swedish)

A Thermal Response Test (TRT) is conducted in order to establish some critical parameters needed to calculate the dimensioning (number, geometric configuration, depth and spacing of the bore holes) of the Bore Hole Thermal Energy Storage (BTES) as  accurate as possible given certain heating and cooling loads.

If not conducted these parameters has to be estimated on basis of whatever clues that exists.  For e.g. granite and other igneous rocks the values can vary substantially and the effect is that the size of BTES (amount of bore holes and/or meters drilled) can vary with as much as 30 percent. So without a TRT the BTES can be either over seized, unnecessarily expensive or under sized, not being able to deliver the necessary amount of heating and cooling.

What is measured is the temperature , the conductivity, and the Thermal bore hole resistance.

Temperature is the undisturbed average temperature in the bedrock along the bore hole, in degrees Celsius.

Conductivity, commonly named lambda, is the bedrocks ability to conduct heat  as an average along  the length of bore hole. It is measured in W/mC (Watt per degree Celsius or Kelvin and per meter).

Bore hole resistance is measured in Cm/W and is of course also an average value. Bore hole resistance is the barrier for heat transfer that exists between the fluid in the heat exchanger and the wall of the surrounding rock. Effectively it shows the temperature difference between the fluid and the rock wall that will almost immidiately be established, depending on the power of the heat that is added, or extracted, from the bore hole.

These parameters describes the thermal properties of the bedrock surrounding the bore hole well enough to be used in a simulation model, e.g. Earth Energy Designer, for dimensioning the BTES (EED is described in another document).

In order to conduct a TRT one bore hole need to be drilled. That bore hole can later on be used in the BTES so it is not a additional cost.

The drilling of a bore hole, apart from enabling a TRT, also gives valuable information about the properties of the bedrock like the subterranean water level, fissure zones, type of rock (soft, hard etc), pressure  etc  which greatly helps when the cost for drilling the entire BTES  is calculated.