Dynamic Heat Transfer and Thermal Storage Characteristics of Ultra-Thick Rammed Earth Walls under Summer Natural Ventilation on the Tibetan Plateau
Abstract
Traditional ultra-thick rammed earth walls in the Tibetan Plateau region show excellent thermal performance under extreme climatic conditions such as strong solar radiation, low-pressure hypoxia, and drastic temperature difference between day and night, but their dynamic heat transfer and energy regulation mechanism under the action of unsteady bidirectional thermal perturbation in the plateau still needs to be studied in depth. In this study, a three-dimensional unsteady two-way thermal coupling model of traditional rammed-earth dwelling walls in Shangri-La, Northwest Yunnan Province, was constructed based on the special climatic characteristics of the plateau, and the spatial and temporal heterogeneity law of heat transfer of the ultra-thick rammed-earth wall in summer and its heat storage/exothermic coupling mechanism were systematically elucidated. The results show that (1) the depth of influence of the external heat wave is 500 mm, and the depth of influence of the internal heat wave is 200 mm. (2) The standing wave node at the depth of 400 mm leads to the cyclic reversal of the direction of the heat flow, which delays the peak of the external temperature wave by 855 min (58.3% of the cycle), and the time lag of the extreme temperatures at different depths is predicted by the fitted function. (3) This wall can reduce interior temperature fluctuations by 73.6% to 77.5% through asymmetric heat transfer and high thermal storage properties, providing a core thermal buffer capacity for highland buildings. This study can provide a theoretical basis for dynamic thermal regulation of highland buildings to cope with climate extremes.