Thermal Response Test Analysis for an Energy Pile in Ground-Source Heat Pump Systems

A thermal response test (TRT) analysis for a cylindrical energy pile (CEP) was carried out in order to determine the thermal properties of the materials in different regions of the system being modelled. Sample test data were generated by using a three-dimensional numerical model of the CEP. Various combinations of the materials inside and outside the CEP were investigated. It was found that the thermal properties of both the CEP and the surrounding soil could be determined with sufficient accuracy. This was important as the effective thermal properties of the CEP depended on the design of the CEP which could be very difficult to determine by other means. Another study was made to explore the possibility of assuming a homogeneous material outside the pipes with the adoption of equivalent thermal properties determined from the TRT analysis so that an analytical modeling approach could be employed. A comparison of the simulation results was made for the CEP based on the specified thermal properties of the various regions with those for the case in which the equivalent thermal properties was used. By applying a cooling-dominated annual periodic load profile, it was found that the simulated temperature of the fluid leaving the CEP could differ substantially. This meant that the assumption of a homogeneous material outside the pipes could lead to erroneous results.