Long-term dynamic heat transfer analysis for the borehole spacing planning of multiple deep borehole heat exchanger

Abstract

In this paper, based on the heat transfer characteristics of deep borehole heat exchanger (DBHE), the superposition dimension reduction algorithm was used to solve the heat transfer model of multiple DBHE (MDBHE). Compared with the monitoring field data, the simulation results calculated by using the superposition dimension reduction algorithm are accurate and reliable. Meanwhile, its computation speed is 4 orders of magnitude faster than that of commercial software. This algorithm was also used to simulate the influences of borehole spacing on long-term heating performance of a DBHE composed of four boreholes, and the results were compared with a single-borehole DBHE, which indicate that increasing borehole spacing can effectively reduce the thermal disturbance among boreholes and enhance heat extraction capacity. When the borehole spacing among MDBHE increases to 50–60 m, the differences of inlet fluid temperature, soil temperature and borehole wall temperature between multiple and single DBHE are obviously reduced. Therefore, the superposition dimension reduction algorithm can quickly and efficiently solve the underground heat transfer problem of MDBHE, which can provide a fast calculation method and theoretical basis for engineering design of borehole spacing. It is recommended that borehole spacing to be 50–60 m if ground area is enough.