Heat extraction capacity and its attenuation of deep borehole heat exchanger array

A model is proposed to analyze the heat transfer of deep borehole heat exchanger (DBHE)arrays. Based on this, a dimension reduction algorithm is proposed for the numerical simulation of heat transfer of DBHE arrays, which can improve calculation speed by several orders of magnitude compared with that by the CFD software. An index of heat extraction capacity (HECI) is adopted to evaluate the heat extraction capacity of DBHE arrays. The influence of borehole spacing, operation time, annual heating duration, terrestrial heat flow rate, borehole depth, soil thermal parameters, pipe diameter and circulating fluid flow rate on DBHE array heat extraction capacity and its attenuation are analyzed. The results show that the borehole spacing, operation time, and annual heating duration all have apparent influence on DBHE array heat extraction capacity and its attenuation rate, while the others only have apparent influence on the heat extraction capacity. According to the calculation results, when the DBHE arrays have a service lifetime of 20–50 years, the recommended borehole spacing range is 40–70 m. •The heat transfer model of deep borehole heat exchanger (DBHE) arrays in cylindrical coordinate system is established.•The calculation speed of the model is several orders of magnitude faster than Ansys Fluent.•An index (HECI) is prosed to evaluate the heat extraction capacity of DBHE.•Borehole spacing, annual heating duration and total operation time significantly affect HECI and its attenuation.•When the DBHE arrays have a service lifetime of 20–50 years, the recommended borehole spacing range is 40–70 m.