Simplified heat transfer analysis method for large-scale boreholes ground heat exchangers

A simplified heat transfer method to analyze the thermal performance of large-scale boreholes ground heat exchangers (GHE) has been proposed considering the geometric symmetry of borehole layout. Taking the ground heat exchanger with matrix layout of vertical boreholes as the example, the ground temperature distribution is analyzed under the conditions of no groundwater advection by the proposed simplified method. Based on the simulation results, a representative boreholes matrix can be proposed to replace the original large-scale ground heat exchanger for heat transfer analysis. Meanwhile, the results show that the representative boreholes matrix can be determined by the thermal influence radius of a single borehole by assuming all the boreholes have the same thermal loads and also in the same geological conditions, geometry parameters and operating conditions. It is indicated that the thermal influence radius of a single borehole can be obtained according to the allowed error range of the ground temperature responses, which can correspondingly determine the number of the representative boreholes matrix.