Effect of the heat load distribution on thermal performance predictions of ground heat exchangers in a stratified subsurface

Thermal performance predictions of ground heat exchangers (GHEs) can be largely affected by the ground stratification and the heat distributions. Based on a validated laboratory device, predictions from numerical models with variable (Q v ) and constant (Q c ) heat transfer rates along the depth of GHEs were compared against the experimental data. The model with Q v gave a more accurate prediction on the ground temperature, while the Q c model weakened the ground stratification effect and overpredicted the clay temperature by up to 76.6%, especially at the late stage. These models predicted different ground temperature distributions at various locations and time. Specifically, for a two-layered structure in this study, the sand temperature predicted by the model with Q v was higher than the clay one, while the Q c model witnessed an opposite trend and more severe thermal interference in both layers at the end of the 24 h operating period. Furthermore, a comparison of the models with layered and equivalent material reveals that the effect of axial heat load distribution could be more significant on the heat transfer of a stratified subsurface. Therefore, it is recommended to apply the variable axial thermal exchange distributions for heat transfer predictions of GHEs in a layered ground.