Numerical research on thermal response for geothermal energy pile groups under groundwater flow

A 3D numerical heat transfer model is established and validated to investigate the effect of groundwater flow on the thermal response of geothermal energy pile (GEP) groups. A constant heating flux with different groundwater flow velocities is applied to four common types of GEP groups in residential buildings. The results show that groundwater flow has an effect on the thermal performance of GEP groups, and the average coefficient of performance of the GEP groups has an increase with groundwater flow. In the short-term (e.g., a month), the GEP spacing of 3 times the pile diameter is convenient from the viewpoint of energy when the flow velocity is less than 0.01 m/yr. The amount of heat is carried from upstream GEPs to the downstream by groundwater flow, and the temperature difference between the upstream and downstream GEPs becomes more obvious with the increase of groundwater flow velocity. In addition, we discussed the differential thermal expansion caused by groundwater flow and its effect on the mechanical behavior of GEPs.