Numerical modeling of a simplified ground heat exchanger coupled with sandbox

The ground heat exchanger (GHE) system is an energy-efficient application employing the geothermal energy in residential and commercial buildings. Compared with field tests or laboratory measurements, computational fluid dynamics and heat transfer offers a cost-effective approach to give accurate prediction on thermal performance assessment of the GHE system. In this study, the effects of different boundary configurations were numerically investigated based on a referred laboratory GHE experiment. First, both recorded input water temperature profile and the given heat load were used as heat input for numerical simulations, and all facets of the ground domain were set as adiabatic condition. Through comparing the numerically predicted output water temperature profile with the experimental recorded one, the first approach using the recorded input water temperature profile as heat input gave a close prediction with the experimental data, while the numerical results based on the second approach using the given heat load showed a considerable discrepancy compared with experimental data. This comparison discrepancy can be attributed to the adiabatic assumption for the ground domain facets through heat balance analysis, and can be addressed by introducing a dynamic thermal boundary configuration for side- and end-walls. This study demonstratedthe significance of boundary conditions consideration and provided a solution by utilizing dynamic thermal boundary treatments compared with the adiabatic assumption. The numerical modeling methods can contribute towards improved GHE numerical simulations based on finite ground domains.