Numerical analysis of ground temperature response characteristics of a space-heating ground source heat pump system by utilizing super-long flexible heat pipes for heat extraction

In this work, the ground temperature variation characteristics of a ground source heat pump system equipped with super-long flexible heat pipes for the extraction of shallow geothermal energy were inves-tigated by computational fluid dynamics for the application of space heating. The study was based on the dynamic analysis results from the coupling of the thermal resistance model of super-long flexible heat pipes and the heat pump performance. The effects of groundwater advection, soil thermal properties, the layout of super-long flexible heat pipes, and the operational conditions were considered. Results show that groundwater advection plays the most important role in the variation of soil temperature. With no activity of groundwater advection, the ground temperature near boreholes continuously decreased throughout the heating season from approximately 290.6 K to 279.3 K, and it cannot recover to the initial temperature before the end of the transition season. The area of thermal plume of the upstream boreholes is much smaller than the downstream under the influence of groundwater advection. The thermal interaction of boreholes in the vertical direction of groundwater advection almost disap-peared when the advection velocity exceeded 0.5 m/d. The cold accumulation near the boreholes can be alleviated under the intermittent operation by reducing the working time. The high soil thermal con-ductivity weakened the cold accumulation phenomenon. This work provides a theoretical basis for the optimization of the design and installation of ground source heat pump systems equipped with super-long flexible heat pipes. (c) 2021 Elsevier B.V. All rights reserved.