Numerical and analytical analysis of groundwater influence on the pile ground heat exchanger with cast-in spiral coils

Abstract

With widespread application of ground-coupled heat pump (GCHP) system, heat transfer process of pile ground heat exchanger (PGHE) has attracted much attention. Previous researches, studying the impact of groundwater flow, mainly focus on the PGHE with cast-in U-T ubes. However, compared with the PGHE with U-T ubes, PGHE with castin spiral coils has better heat transfer performance and is more suitable for a modern city with high building density. Therefore, in this paper, a 3-D simulation model and a simplified analytical model are established to investigate the influence of groundwater flow on the thermal performance of PGHE with cast-in spiral coils. A comparison between these two models is carried out. Both numerical and analytical results show that the groundwater flow has an enhancing effect on the heat transfer performance of the PGHE with spiral coils and can accelerate the heat transfer process into stability. When the seepage velocity is 1e-5 m/s, the average enhancing rate is 22.98%.