Influence of underground drop seepage on temperature field in the buried pipe zone and performance of ground source heat pump system

In order to reveal the influence of underground drop seepage on changing features of temperature field in the buried pipes zone and the performance of the ground source heat pump (GSHP) system in winter and summer conditions, a three-dimensional mathematical model of heat transfer of buried pipe heat exchanger (BHE) with groundwater seepage was established according to the energy-mass conservation. The evolution of the underground temperature field under different seepage conditions was analyzed through the model; the performance change characteristics of the GSHP system in winter and summer was analyzed on the basis of TRNSYS. The research results show that the heat (or cold) accumulated around the buried pipes gradually migrates to the downstream in the direction of groundwater flow in an ellipse shape under the action of seepage. The heat transfer power per unit depth of BHEs gradually increases with increasing seepage velocity, which are linearly related. It indicates that the heat (or cold) accumulation phenomenon is significantly reduced by groundwater seepage. When the seepage rate reaches 2.5 x 10-4 m/s, the coefficient of performance (COP) of the GSHP system in winter and summer increases by 12.89 % and 10.71 %, respectively. The results show that seepage can effectively alleviate heat accumulation and improve the heat transfer efficiency of GSHP, which provides guidance and reference for the engineering application of GSHP under groundwater seepage.