Design and development of a low-cost thermal response rig

A thermal response test is a controlled in situ test during which a known quantity of heat energy is injected into a closed loop heat-exchanger pipe while the heat dissipation rate into the surrounding ground is monitored. Results from a test can be interpreted to determine a number of ground thermal parameters that are vital design requirements for any medium- to large-scale ground-source energy system. This paper describes the design and construction of a low-cost thermal response test rig and compares the results obtained from a test using the constructed rig and a commercially built rig in order to evaluate the accuracy of the constructed equipment. The thermal response test rig is designed in accordance with the following principles: keep construction costs low, improve the cost-efficiency of thermal response test testing by incorporating remote data transmission capability and ensure attainment of sufficient accuracy to satisfy the design requirements of ground-source energy systems. Analysis of data collected by the thermal response test rigs results in a calculated thermal conductivity of 1·9 W/mK in both cases. This value falls within the range expected for the tested geological formation and confirms the accuracy of both test rigs.