Study On The Hygrothermal Performance Of The Earth Structure Wall With Passive Regulating Humidity In Northwest Of Sichuan

In the context of the continuous growth of building energy consumption,the earth material has attracted people’s attention again because of its characteristics of green environmental protection and sustainable development in recent years.The modern technology of earthen building is developing rapidly.In view of excellent hygrothermal performance of the earthen material,the aim of this project is to improve the database of heat and moisture physical parameters of the earthen material in Northwest Sichuan and reveal the characteristics of coupled heat and moisture transfer inside the earth wall and the regulation mechanism of the earth wall on the indoor hygrothermal environment.Firstly,the hygrothermal parameters(density,thermal conductivity,specific heat capacity,water vapor permeability and isothermal absorption curve)of the earth material in Northwest Sichuan were tested.The hygrothermal performance of the earthen material was compared and analyzed by using the measured hygrothermal parameters with other common building materials.The results show that the earthen material has the more potential to adjust indoor relative humidity and attenuate outdoor temperature fluctuation.Secondly,based on the previous research,a coupled heat and moisture transfer model for the earth wall considering the influence of relative humidity on latent heat of phase change in the pores of the earth material was established.And the indoor air heat and moisture balance equation in the earthen buildings considering the wall absorption/desorption moisture was developed.The accuracy of the numerical model is verified by comparing with the experimental data and literature results.And then the heat and moisture transfer characteristics of the earth wall under different boundary conditions were studied by using the coupled heat and moisture transfer model of the earth wall.Furthermore,the thickness of the earth wall in Northwest Sichuan was optimized.The results show that the temperature and humidity change of the environment will affect the temperature and humidity distribution inside the earthen wall and the heat and moisture exchange on the surface.The greater the moisture exchange capacity is,the more significant the effect on heat transfer will be.Additionally,the best thickness of the earth wall in Northwest Sichuan is 500 mm,which can effectively reduce the outdoor temperature and humidity fluctuation.The time delay in summer and winter is 8 hours and 12 hours respectively.Next,the hygrothermal performance of the common earth wall and that with the moisture barrier on the external surface were analyzed,which focuses on the effects of the moisture barrier on the hygrothermal performance of the wall.The results show that the moisture barrier makes the moisture content of the wall increases and reduces the moisture exchange capacity of the internal surface of the wall.The capacity of moisture regulating the humidity of the wall thus reduces,but it can reduce the heat loss by up to 5%.For the common earth wall,on the premise of meeting the human comfort,the indoor relative humidity should be reduced appropriately to achieve the purpose of energy saving.The earth wall with the moisture barrier has the best energy saving effect when the indoor air relative humidity is equal to 50%.Moreover,it is more suitable to install the moisture barrier on external surface of the wall when the wall facing west.Finally,the numerical simulation of the indoor hygrothermal environment in the earth building with the internal surface is equipped with different coating layers(no coating,plasterboard,waterproof paint)were carried out.The results show that the fluctuation range of the indoor air relative humidity under these three conditions are 20%,37.8% and 40.4% respectively.The time of indoor air relative humidity in the range of 60-80% accounts for 84.9%,70.4%,and 60.5% of the whole year respectively.The absorption and desorption of the earth wall without inner layer can effectively reduce the fluctuation range of indoor relative humidity and regulate the indoor relative humidity.Moreover,its absorption and desorption amount is three times of that of gypsum board.The use of wall decoration materials will make the earth wall reduce or even lose the ability of regulating indoor relative humidity.