Numerical thermal investigation on pile ground heat exchangers with groundwater seepage

Groundwater flow has a considerable impact on the thermal performance of the pile ground heat exchangers (PGHE) of a ground coupled heat pump system. However, available research studies, which took groundwater advection into consideration in the thermal analysis of the PGHEs, mainly focused on the PGHE with U-tubes. The spiral coil configuration has more heat transfer area in a certain pipe and better flow pattern compared with the U-tube PGHE. Therefore, in this study, a 3-D transient numerical model is established to investigate the thermal performance of the spiral-coil PGHE with groundwater advection. The influences of the hydraulic and thermal properties of the soil on the PGHE are also evaluated by means of the numerical model in the porous medium. Comparison with existing analytical solutions based on the ring-coil heat source is carried out. The simulation results suggest that the seepage flow greatly enhances the heat transfer performance of the geothermal heat exchangers. The strengthening effect is proportional to the hydraulic gradient and is found to be more obvious on the spiral coil system than the U-tube system.