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As environment-friendly building materials, earth materials are attracting significant attention because of their favorable hygrothermal properties. In this study, the earth materials in northwest Sichuan were tested and curves of thermal conductivity and water vapor permeability with relative humidity were obtained. The function curves and constants of the two coefficients were substituted into the verified nonstationary model of heat and moisture transfer in rammed earth walls and indoor air for calculation. The difference in the calculation results when the hygrothermal parameters are functions and constants were analyzed, and the influence of the non-constant hygrothermal parameters on the heat and moisture transfer in rammed earth walls, was obtained. The test results show that thermal conductivity is linearly related to moisture content, and water vapor permeability has a small variation in the relative humidity range of 0–60% and increases exponentially above 60%. The calculation results indicate that the non-constant hygrothermal parameters have little influence on the internal surface temperature of the rammed earth walls and Mianyang City's indoor air temperature and humidity during the summer and winter. The heat transfer on the internal surface will be underestimated by using a non-constant for the hygrothermal parameter when the moisture content of the wall is low, and vice versa. In hot-humid areas or seasons with large differences in temperature and humidity between indoors and outdoors, non-constant hygrothermal parameters have a more obvious effect on heat transfer on the internal surface of the wall. The results of this study demonstrate the necessity of parameter testing. [ABSTRACT FROM AUTHOR]

Building construction accounts for 40% of the global anthropogenic greenhouse gas emissions. The drastic increase in the energy costs of building materials has drawn attention to earth materials, such as rammed earth. In this study, the hygrothermal properties of rammed earth in the Tibetan Autonomous Prefecture, Sichuan Province, China were measured and compared with results from previous studies. To analyze the hygrothermal performance of a rammed earth wall, a numerical model was established and verified. The coupled heat and moisture transfer in the area of the common rammed earth wall and the moisture barrier wall was simulated with different indoor conditions, orientations, and thicknesses. The numerical results were observed to be consistent with the experimental data. In contrast to results from other studies, the earthen material analyzed in this study exhibits less vapor transfer, but better thermal stability and moisture buffering. The moisture barrier increases the average moisture content of the rammed earth wall, but reduces the maximum moisture content, thereby protecting the wall. The moisture barrier probably also reduces the moisture buffering capacity of the wall. The moisture barrier has no significant effect on heat transfer; even a west-facing wall reduces heat loss by only 3% in this area. • The studied earthen material has lower diffusivity and higher effusivity. • The moisture barrier results in a maximum reduction in moisture transfer of 35%. • The increase of moisture transfer reduces the heat loss of the wall for the whole year. • The moisture barrier will be more effective used on rammed earth wall facing west. [ABSTRACT FROM AUTHOR]