Properly shortening design time scale of medium-deep borehole heat exchanger for high building heating performances with high computational efficiency

The medium-deep borehole heat exchanger (MDBHE) is a clean solution for building heating with renewable geothermal energy. The long-term performance evaluation with the design time scale same as the life span of the MDBHE is generally adopted by the MDBHE design for high heating performances. However, the long-term performance evaluation largely increases the computational load of the MDBHE design, resulting in practical inconvenience. This study proposes the idea that properly shortening the design time scale could maintain the information of the long-term performance evaluation for the MDBHE design with high heating performances while reducing the computational load. The idea is verified by the MDBHE design for building heating in the severe cold zone of China. The multiple design parameters of the MDBHE are simultaneously optimized considering climate change. The results show that under different geological conditions, economic conditions, and system safety requirements, compared with the life span of the MDBHE of 30–50 years, the design time scale properly shortened to 10 years achieves similar high heating performances regarding the energy consumption, cost, and system safety, and reduces the computational load by 66.1 %–79.3 %. This study contributes to high computational-efficient and high-performance design of the MDBHE for building heating.