The Exploration on Heat Transfer Models for Borehole Heat Exchanger in the Soil with Groundwater Advection

Abstract

In order to estimate the impact of groundwater advection and axial heat conduction on the performance of borehole heat exchangers in ground source heat pump systems, results obtained from different heat transfer models of a vertical borehole heat exchanger based on line source theory were compared. It is found that the analytical solution from the moving finite line source (MFLS) model reveals the fact that soil temperature field around the borehole migrates along the ground-water advection direction and more obvious variation of the vertical temperature change occurring near the ground surface and the borehole bottom. It means the MFLS model can be used when groundwater advection presents. The results are also validated by 3-D numerical simulation. In addition, the influence of groundwater advection on the soil temperature responses is also analyzed. A larger advection velocity causes the soil temperature to change faster and to achieve a lower stable temperature change as time elapses.