Application of the medium-deep borehole heat exchanger (MDBHE) coupled ground source heat pump (GSHP) system on building heating has been gradually accepted by public and its sustainability becomes a key concern. In this work, a long-term transient heat transfer model for the MDBHE coupled GSHP system is proposed to investigate the effects of various influencing factors on the thermal extraction and energy efficiency of this system. Sensitive analysis highlights the significant effects of the specific heat transfer rate, rock-soil thermal conductivity, geothermal gradient, pipe depth and fluid velocity on the annual decline of the system performance during its long-term operation. Furthermore, the operation optimization for this system should be conducted based on its performance in quasi-steady state. An optimal fluid velocity exists to acquire the maximum specific heat transfer rate of MDBHE under a constant Seasonal Performance Factor of Heat Source (SPF₂). In order to guarantee an efficient thermal extraction, the comprehensive effects of both specific heat transfer rate and fluid velocity on the energy efficiency should be taken into account. For the benchmark MDBHE, the operation condition is optimized with the specific heat transfer rate of 142 W/m, and the fluid velocity of 0.7 m/s; the annual SPF₂ is always greater than or equal to 4.0 during the long-term operation, which ensures a sustainable and efficient operation.

中等深度井下换热器（MDBHE）耦合地源热泵（GSHP）系统在建筑采暖中的应用已逐渐为公众所接受，其可持续性成为一个关键问题。在这项工作中，提出了MDBHE耦合GSHP系统的长期瞬态传热模型，以研究各种影响因素对该系统的热提取和能效的影响。灵敏的分析突出了在长期运行过程中，特定的传热速率，岩土导热系数，地热梯度，管道深度和流体速度对系统性能逐年下降的重大影响。此外，应根据系统在准稳态下的性能对其进行操作优化。₂）。为了保证有效的热量提取，应考虑比热传递速率和流体速度对能量效率的综合影响。对于基准MDBHE，以142 W / m的比热传递速率和0.7 m / s的流体速度对操作条件进行了优化。长期运行期间，年度SPF ₂始终大于或等于4.0，从而确保了可持续且高效的运行。