At present the medium-deep borehole heat exchanger (MDBHE) performance was usually analyzed under the typical condition that inlet fluid temperature is deemed as constant. In practical application, inlet temperature is often related to the heating load. In this paper, the effects of heating load on the heat transfer performance of the MDBHE was investigated based on the proposed numerical model which has been validated. The sensitive analysis was implemented to analyze the variation regulations of inlet and outlet temperatures of pipe and thermal effect radius of rocksoil under different heating loads. Furthermore, the MDBHE performance was compared between the two scenarios: constant heating load and constant inlet temperature. The simulation results indicated that under high heating load, the fluid temperature of MDBHE varies substantially during the heat transfer process. Besides, annual drop of inlet temperature should be paid attention. The rock-soil temperature in vertical direction was influenced significantly by the heating load, while the thermal effect radius of rock-soil was affected slightly.
Keywords heating load, heat transfer, medium-deep, borehole heat exchanger