Study on Thermal Resistance of Coaxial Tube Boreholes in Ground-Coupled Heat Pump Systems

摘要

Taking the fluid temperature distribution along the borehole depth and thermal short-circuiting into account, a new model for coaxial tube borehole heat exchangers has been established, which provides a better understanding of the heat transfer processes in the ground heat exchangers. On this basis the borehole resistance and efficiency of the borehole heat exchanger have been defined, and their analytical expressions derived. Impacts of different constructional and operational parameters on borehole performance are analyzed and discussed. The concept and explicit expression of thermal resistance of the coaxial tube borehole provides an essential and appropriate means for thermal analysis and engineering design of the ground-coupled heat pump systems with coaxial tube boreholes.