Impact of the Seasonal Variations in Ground Temperature on Thermal Response Test Results

Abstract

© ASCE. Due to the prevalent use of the thermal response test (TRT) for estimating the key design parameters of ground source heat pump systems, it is important to understand how external factors may impact on their accuracy. The infinite line source model (ILSM) is typically used to interpret TRT data, relying on many simplifying assumptions, which when violated may lead to errors in the results. Seasonal variation causes the ground temperature profile to vary significantly at the surface, with decreasing effect at increasing depth, while the ILSM assumes this profile is constant. A numerical study of ILSM performance under different seasonal conditions using a state-of-the-art FE model is presented. The study aims to determine if TRT interpretation may become misleading when tests are conducted at different times of the year. Results suggest there is little variability in effective thermal conductivity, but up to ~50% in GHE thermal resistance, and as much as ~9°C in mean fluid temperature.