Enhancing thermal insulation and energy efficiency in low-temperature granaries using pipe-embedded envelopes

Low-temperature granaries enable long-term, high-quality grain storage by maintaining controlled indoor conditions. However, significant energy is required to counteract the temperature difference between the interior and exterior. This study investigates the thermal insulation performance of an integrated pipe-embedded envelope, incorporating exterior walls and roofs. Scaled model experiments and simulations assess the effects of water flow rate, inlet water temperature, and pipe spacing on thermal performance and energy efficiency of the envelope. Results show the proposed envelope reduces heat gain by over 30 % compared to conventional designs. A nonlinear correlation is observed where an increase in the envelope's volumetric water content significantly reduces heat gain, while water temperature has a greater impact on heat transfer than flow rate, displaying a linear relationship under fixed conditions. Moreover, decreasing the spacing between embedded pipes improves thermal insulation performance. When the ratio of the inter-pipe distance to the length of the envelope in the direction of pipe arrangement is less than 1/18, the structure can provide free cooling when combined with evaporative cooling. Using water 2 °C above indoor air temperature cuts cooling energy use by 47.9 %. This research provides insights for optimizing pipe-embedded systems in low-temperature granaries and integrating them with low-grade energy sources.