Numerical analysis of moisture buffering performance and long-term dynamic assessments in naturally ventilated underground shelters

One of the primary tasks in the regular maintenance of underground shelters is to ensure proper internal environmental conditions, as humidity is a major obstacle for sustainable use. This study aimed to develop a passive method that combined hygroscopic materials with natural ventilation to improve the indoor humidity of underground shelters. Using a coupled model that included heat and moisture transfer in hygroscopic materials, dynamic heat and moisture transfer in underground buildings, and multizone airflow, this study analyzed the moisture buffering performance of hygroscopic materials under different ventilation conditions. This study also introduces the annual moisture buffering effect as an indicator of humidity stability, which allows a more comprehensive reflection of the material's overall performance in responding to repeated humidity fluctuations in real-world environments, making it particularly suitable for engineering structures such as underground shelters. Simulation results showed that straw-based boards exhibited 2.4–3.1 times higher moisture buffering effect than inorganic materials. Passive measures combining natural ventilation with hygroscopic materials could fully meet humidity requirements in severely cold, cold, hot summer and cold winter, and temperate zones, but were insufficient to fully resolve the humidity problems in the hot summer and warm winter zone.