Ground Source Heat Pumps (GSHP) are becoming an increasingly popular technology. Society is transitioning away from fossil fuel heating systems (gas and oil-fired boilers), causing an acceleration in demand for low and zero carbon solutions.

With a GSHP system, it is important to accurately calculate the number and depth of boreholes needed. If too few boreholes are drilled, or if the boreholes are not deep enough, the system will be inefficient and won’t provide enough heat to the property.

Why is a Thermal Response Test needed?

The specification for the borehole array partly depends on the property itself (size of the property, insulation, window glazing etc). It also depends on the thermal properties of the geology. To understand these thermal properties, a Thermal Response Test can be carried out.

A Thermal Response Test (TRT) is often carried out when the geology beneath the site is not well-known, or where the heat demand for the property is expected to be especially high (large houses, schools, hospitals, etc).

How is a Thermal Response Test carried out?

A borehole will be drilled to a pre-determined depth, usually between 100 and 200 metres below ground level. Once drilled, a geothermal collector (usually 40mm polyethylene pipe with a u-bend) is installed to the depth of the borehole. The collector loop is pressure-tested after installation and the borehole is backfilled with thermal grout.

Once the drilling and installation is complete, it will then be time to run a Thermal Response Test on the geothermal borehole. This involves circulating a special fluid into the geothermal collector loop to gather data on the thermal performance of the borehole. This includes its thermal conductivity and resistance.

This data is then analysed, with recommendations for the full GSHP system presented in a summary report. These recommendations will help the designer to more accurately calculate the number and depths of boreholes required for the full GSHP system.

What should be the duration of a Thermal Response Test?


A Thermal Response Test typically runs for 48 hours, however the duration may be longer depending on the specific needs of a project.

When should a Thermal Response Test be carried out?


A Thermal Response Test is usually required early in the process, so the designer can calculate the requirements for the Ground Source Heat Pump system and boreholes.

The most cost-effective and convenient time to conduct a TRT is usually when a geotechnical ground or mining investigation is taking place on site. This is because the same drilling rig needed for these investigations can often be used to drill the geothermal borehole too. This reduces mobilisation costs, resulting in an overall saving for the client.

If a TRT is not carried out during the ground investigation, it can still be carried out later as a standalone service. In our experience it makes sense, however, to carry out the TRT earlier in the process.

Can Hydracrat carry out Thermal Response Tests?


Hydracrat can arrange for a full Thermal Response Test to be carried out. This includes the drilling, installation of the geothermal materials, on-site Thermal Response Test and provision of the TRT report.

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