Effects of building load characteristics on heating performance of the medium-deep U-type borehole heat exchanger coupled heat pumps: A coupled dynamic simulation

The medium-deep U-type borehole heat exchanger (MDUBHE) coupled ground source heat pump to extract deep geothermal energy for heating buildings is a novel and efficient system. However, the current research focuses on the heat transfer of the main apparatus MDUBHE and ignores the dynamic coupling and matching between the system and the building load, resulting in the effect of the building load characteristics on the system performance and the rock-soil temperature is still unclear. Therefore, this study first integrated the MDUBHE model into the Trnsys platform to realize the coupled simulation of building loads with the MDUBHE system. Based on the integrated novel platform, the effect mechanism of building load characteristics on the system's operation and the rock-soil temperature is revealed. The results show that the water temperature, flow rate, heating capacity, and system efficiency under dynamic actual load conditions are significantly different compared to constant building loads. The inlet and outlet temperatures varied in the ranges of 15.4–34.5 °C and 20.7–40.5 °C, respectively, and the flow rates on the user side and the ground source side varied in the ranges of 4.6×104–2.2×105 kg/h and 3.7×104–1.6×105 kg/h, respectively. In addition, the heating capacity varies from 0.1×103–3.6×103 GJ, and the unit performance varies hourly. Furthermore, the soil temperatures also respond to changes in the actual building loads, but the variation is insignificant with increasing radial distance due to heat conduction. This study provides a foundation for matching the system capacity with the building loads.