A Simulation Model for Coupled Heat Transfer and Moisture Transport under the Action of Heat Source in Unsaturated Soils

Ground source heat pump (GSHP) system has been installed as the air-conditioning system worldwide due to it has the characteristics of high efficiency, easy access and environmental protection. Since ground heat exchanger (GHE) plays a key role in the performance of GSHPs, many models of GHE have been proposed to simulate temperature distribution around the borehole. However, most of these models depict only the heat conduction process between buried pipes and surrounding soil based on the line source model or cylindrical source model. And these models do not consider water transfer under the action of heat source, which can cause some prediction errors. The objective of this study is to provide a numerical model to simulate the spatiotemporal distribution of temperature and moisture caused by a GHE with constant temperature in unsaturated soils. The numerical model is developed by establishing two tridiagonal matrices and adopting Thomas algorithm to achieve the programming. The experiment is operated at the Taiyuan University of Technology and the comparisons between modeled and experimental data prove the high accuracy of this model. The model shows significant engineering values in designs and operations of GSHP.