A Case Study on Grain Storage in Underground Granaries with Different Lining Materials

• Polypropylene Lining Minimizes Condensation Risk: Compared to stainless steel, a polypropylene lining maintains a higher internal temperature (max. +1.5°C) and lower relative humidity (max. -7.1%), leading to more stable thermal conditions and effectively reducing the risk of wall condensation. • Ranks Cooling Performance of Common Waterproof Materials: Numerical simulations rank the cooling effectiveness of lining materials as: Stainless Steel > Asphalt > Polyethylene > Fiberglass > Polypropylene, providing a clear guideline for material selection based on thermal conductivity. • Identifies Thermally Sensitive Boundary Zone: A critical region extending approximately 0.3 meters inward from the granary walls is identified, where the choice of lining material has the most significant impact on local temperature and humidity distributions. • Validates a CFD Model for Underground Granary Design: The study establishes and validates a Computational Fluid Dynamics (CFD) model, which serves as a reliable tool for simulating and optimizing the hygrothermal environment in underground grain storage systems. Underground granaries are environmentally friendly structures that utilize shallow geothermal energy for grain storage. They enable long-term low-temperature (≤15°C) or quasi-low-temperature (≤20°C) storage by harnessing natural ground temperature, thereby reducing fossil energy consumption. This study designed a simulated experimental system to investigate the effect of different waterproof lining materials on condensation formation on the inner walls of underground granaries under quasi-static, non-intervention conditions. Tests were conducted under three continuously varying external environmental phases. The results indicated that external environmental influence is more pronounced in shallow-buried granaries, leading to a "cold skin–warm core" temperature distribution within the grain pile, especially in the upper part. Compared to the stainless steel lining, the polypropylene lining resulted in a higher internal temperature (maximum difference: 1.5°C), lower relative humidity (maximum difference: 7.1%), and a 0.5°C higher average grain temperature. Therefore, polypropylene is considered more suitable as a lining material. Based on experimental data, a comparative simulation was performed for stainless steel, polyethylene, polypropylene, fiberglass, asphalt coating, and bare concrete walls. The simulations showed that the cooling effect followed the order: stainless steel > asphalt > polyethylene > fiberglass > polypropylene. However, considering condensation prevention, polypropylene lining exhibited more stable temperature variations, which helps minimize condensation risk on the granary walls. The findings provide insights applicable to similar underground storage configurations, though further validation is recommended for full-scale engineering applications.