Experimental investigation on energy and resilience performance of spherical PCM-assisted EAHE system for underground buildings

Rapid development of underground spaces has led to a significant increase in energy consumption. Among these, heating, ventilation, and air conditioning (HVAC) systems account for 31%-40% of energy consumption. The reserved pit trenches in the construction process provide a space for the installation of ducts for the fresh air pre-cooling system. Combining the earth-air heat exchanger (EAHE) system with pit trenches reduces installation costs and required ground to utilize geothermal energy. Additionally, adding spherical phase change material (SPCM) enhances the heat storage of backfill materials, mitigating performance degradation from soil heat accumulation. This study proposes a SPCM-EAHE system to explore how SPCM improves daily-work performance and resilience performance under extreme weather events. Therefore, a scaled-down experimental setup is developed to assess its effectiveness under both normal and extreme conditions. The findings indicate that adding SPCM can increase the system by 40.25 % under normal conditions. The of the SPCM-EAHE rises following the increasing inlet temperature but presents opposite trend as the inlet velocity increases. However, when air velocity increases, the system’s cooling capacity also increases. Therefore, both the SPCM-EAHE system’s cooling capacity and the overall temperature reduction will jointly determine the selection of velocity. The average cooling capability during extreme weather events is improved by 28.17% and the system’s recovery afterward is improved with an efficiency of 9.36 %, when SPCM is added to the EAHE system. This study provides application possibilities for practical fresh-air systems in underground building pit trenches and shows that adding SPCM to the EAHE system can successfully enhance system performance in both normal and extreme weather conditions.