Study on Long-Term Performance Sustainability of Medium Deep Borehole Heat Exchanger Based on Simplified One-Dimensional Well Model-A Case Study in Beijing, China

Heating buildings and residences is a low-cost and high-efficiency renewable energy utilization method through the coupling of medium deep borehole heat exchanger and ground source heat pump systems. Since the performance of the medium deep borehole heat exchanger system will gradually decrease during long-term operation, its sustainability becomes a key issue in current research. In this paper, a comprehensive numerical model with a simplified one-dimensional well is established using COMSOL Multiphysics by considering the influence of factors including layered strata, groundwater flow, thermophysical properties, and geothermal gradient. The rationality of the model is verified by the thermal response test data of the medium deep borehole heat exchanger system located in Daxing District, Beijing, China. The outlet temperature of the medium deep borehole heat exchanger system declined by 0.48 degrees C (3.1%) next 20 years of continuous operation. The area greatly affected by heat transfer process is basically within 20 m around the borehole. In the fifth, tenth, fifteenth, and twentieth years, the heat transfer impact scope is about 43 m, 56 m, 74 m, and 84 m, respectively. This study can provide a reference for the performance sustainability of long-term operation of medium deep borehole heat exchanger systems.