In-situ measurement of the thermal properties of soils and rocks can play an important part in developing cost-effective and sustainable designs for closed loop geothermal and ground energy systems. If the designer can use in-situ tests to obtain site-specific design parameters this may allow a less conservative ground loop design and reduce the number of boreholes required, as well as giving the client greater confidence in the whole design process. Conversely, parameters from in-situ tests may indicate that overly optimistic thermal properties are being used in design, allowing the design to be varied to increase ground loop capacity and avoid long term operational problems.

The most appropriate means of determining in-situ thermal properties is a thermal response test (TRT). This involves the injection of a finite amount of heat energy into a closed loop borehole over a period of several days, while monitoring the rate at which heat dissipates into the surrounding ground. During a test the principal parameters measured are: the incoming and outgoing temperature of the heat transfer fluid; the flow rate of the fluid; and the heat energy input.

Test data can be interpreted to provide the following parameters, all of which are necessary for efficient design of closed loop systems.

• The initial ground temperature;
• The thermal properties (specifically thermal conductivity and heat capacity) of the ground around the closed loop borehole; and
• The equivalent borehole thermal resistance.

Our key services include the following:

• Scoping and feasibility studies;
• Trial boreholes;
• Thermal response testing; and
• Design of closed loop ground energy systems.