Ground source heat pump systems employing multiple borehole heat exchangers are widely used in building heating and cooling applications. However, their thermal performance is strongly influenced by subsurface heterogeneity, particularly soil stratification and groundwater seepage, which are often simplified in engineering practice. In this study, a three-dimensional numerical model was developed to conduct a detailed case study on the thermal performance of multiple borehole heat exchangers installed in stratified soils with groundwater seepage. The model was validated against experimental data, with outlet temperature deviations within 0.8%. The effects of inlet water temperature, inlet flow velocity, groundwater seepage velocity, and seepage direction on soil temperature distribution, outlet water temperature, and heat transfer rate per unit borehole depth were systematically investigated under typical engineering conditions. The results show that groundwater seepage significantly enhances heat transfer performance, increasing the unit-depth heat transfer rate by up to 23.1%, while soil stratification leads to non-uniform temperature fields and modifies the thermal interaction between adjacent boreholes. The direction of groundwater seepage plays a critical role, with seepage perpendicular to the borehole arrangement being more favorable for improving the heat transfer performance. Inlet water temperature was identified as the dominant operational parameter affecting heat exchange performance, followed by groundwater seepage velocity and inlet flow velocity. This numerical case study provides practical insights into the thermal behavior of BHE arrays in complex subsurface environments and offers useful references for the design and performance evaluation of GSHP systems in stratified, groundwater-affected sites.
Zhang et al. (2026) studied this question.