An improved analytical model for vertical borehole ground heat exchanger with multiple-layer substrates and groundwater flow

An improved analytical model for vertical borehole ground heat exchanger (BHE) which takes into account effect of groundwater flow in multiple-layer geologies is applied to simulate and analyze the long-term temperature response of soil around BHE with the unbalanced seasonal dynamic load. The present model was validated by experiment for a single borehole with good agreement, and it can find that the average of temperature integral along the borehole wall depth is taken as the representative temperature of the borehole wall will be more reasonable. Moreover, the influence of groundwater flow velocity on soil temperature around the borehole was investigated, the results show that the deformation of plane temperature field caused by groundwater advection, as equivalent velocity reach a certain order of magnitude, groundwater flow can effectively alleviate the heat (cold) accumulation. Finally, the temperature change of soil around borehole at different operation time was simulated, results indicate that the higher the groundwater velocity is, the faster time make temperature field to achieve stability. This analytical model provides better flexibility and versatility to research further the effect of groundwater flow in layered geologies.