Transient simulation and performance analysis for deep borehole heat exchanger coupled ground source heat pump system

In the northern China with cold climate, the deep borehole heat exchanger (DBHE) is widely developed in recent years, which is coupled with ground source heat pump system (GSHP) to supply geothermal energy for building heating. In this study, a new-type DBHE coupled GSHP system model was developed by combining the MATLAB and TRNSYS software. Considering the upper threshold of inlet temperature for the heat pump unit, the control logic between the plate heat exchanger (PHE) and the heat pump unit was designed. Taking space heating of a residential building as a scenario, the operating characteristic and energy performance of system were analyzed. The results show that the PHE operation time during a heating period gradually decreases from 651h to 212h over 10 years. The sudden decrease of PHE operation time will lead to the increase of seasonal performance factor of heat pump. Furthermore, the circulation temperature attenuation of DBHE decreases exponentially with the increase of heat extraction capacity. Moreover, the effects of dynamic and constant building heating load on the system operation and energy distribution relationship were explored. Compared with dynamic heating load, heat extraction capacity of PHE and heat pump under constant load is underestimated and overestimated during heating period, respectively. After 10 years of operation, the difference of heat extraction capacity of system reaches to 5.37 MWh. The results suggest that system performance prediction based on constant heat load has deviation from the real situation.