Design optimization of medium-deep borehole heat exchanger for building heating under climate change

Geothermal thermal energy with a medium-deep borehole heat exchanger (MDBHE) is a clean solution for building heating. There lacks a proper design of the MDBHE based on long-term performance evaluation, which is essential to promoting the efficient application of geothermal thermal energy for building heating. This study proposes a design optimization of the MDBHE for building heating under climate change. First, the long-term heating energy performance of the MDBHE under climate change is evaluated. Second, the operation cost is evaluated based on the long-term heating energy performance, considering the discount rate and inflation rate. Third, an optimization algorithm is employed to determine the optimal design of the diameter ratio of the inner pipe to the outer pipe, pipe depth, and inlet velocity of the MDBHE. The optimization method minimizes the cost of initial and operational expenditure while satisfying the system safety requirement. Results show that climate change should be considered, which helps to robustly reduce energy consumption and cost by 9.3%-44.4% and 3.9%-21.8% respectively, under different design conditions compared with the typical meteorology. This study contributes to the proper design of the MDBHE as a clean building heating solution.