Thermal Response Test
A Thermal Response Test (TRT) is conducted in order to establish some critical parameters needed to calculate the configuration (numbers, geometric configuration, depth and spacing) of the boreholes 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 borehole field (amount of boreholes and/or meters drilled) can vary with as much as 30 percent. So without a TRT the borehole field 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 (often named lambda-value or simply lambda) , and the thermal borehole resistance (borehole resistance for short).
Temperature is the undisturbed average temperature in the bedrock along the borehole, in degrees Celsius.
Conductivity, lambda, is the bedrocks ability to conduct heat on average along the length of a borehole. It is measured in W/mK (Watt per degree Celsius or Kelvin and per meter).
Borehole resistance is measured in Km/W and is of course also an average value. Borehole 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 immediately be established, depending on the power of the heat that is added, or extracted, from the borehole.
These parameters describes the thermal properties of the bedrock surrounding the borehole well enough to be used in a simulation software, e.g. Earth Energy Designer, for configuring a borehole field (the simulation process is described here).
In order to conduct a TRT at least one borehole need to be drilled and a heat exchanger mounted. The borehole(s) can later on be used in the borehole field so it is not a additional cost.
The drilling of a test borehole, apart from making a TRT possible, 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 borehole field is calculated.
Rototec Consulting is using state-of-the-art equipment of its own design. The equipment is connected to “the cloud” and hence everything is monitored in real-time and the measurement result can be downloaded and rapidly analyzed.
Rototec Consulting is following ISO/DIS 17628 standard, the coming EU-standard currently under revision for performing TRTs.