Heat transfer analysis of ground heat exchangers with inclined boreholes

Consisting of closed-loop of pipes buried in boreholes, ground heat exchangers (GHEs) are devised for extraction or injection of thermal energy from/into the ground. Evolved from the vertical borehole systems, the configuration of inclined boreholes is considered in order to reduce the land plots required to install the GHEs in densely populated areas. A transient three-dimensional heat conduction model has been established and solved analytically to describe the temperature response in the ground caused by a single inclined line source. Heat transfer in the GHEs with multiple boreholes is then studied by superimposition of the temperature excesses resulted from individual boreholes. On this basis, two kinds of representative temperature responses on the borehole wall are defined and discussed. The thermal interference between inclined boreholes is compared with that between vertical ones. The analyses can provide a basic and useful tool for the design and thermal simulation of the GHEs with inclined boreholes.