Study On The Influence Of Moisture Migration On Heat Transfer And Indoor Environment Of Earthen Walls In Northwest Sichuan

Against the backdrop of the world’s huge energy consumption,earth materials are seen as one of the building materials most capable of meeting the challenges of a circular economy.In addition,the excellent heat storage and moisture regulation characteristics of earthen architecture can create a good indoor hygrothermal environment.People try to integrate modern technology with traditional earthen architecture.To gain an in-depth understanding of the hygrothermal migration characteristics of earthen building walls in northwest Sichuan,this paper investigates the influence of moisture migration on wall heat transfer and indoor environment using means of experimental measurement and numerical calculation.In winter and summer,monitoring was conducted on the wall and indoor temperature and humidity of full-scale experimental earthen buildings in different stages of completion in northwestern Sichuan.The results show that the indoor relative humidity of the newly built building during the six-months period is consistently above 70%.One year after completion,the moisture content inside the walls decreases significantly,and a more comfortable indoor humidity environment is achieved.The earthen walls exhibit good thermal performance,with average decrements as low as 0.12 for both completed periods walls,and average time lags of7.25 hours and 7.05 hours,respectively.To obtain more accurate hygrothermal parameters of earth materials in northwest Sichuan,the thermal conductivity at different moisture content,specific heat capacity at different temperatures,isothermal equilibrium moisture content,and water vapor permeability under different relative humidity environments were measured.Taking temperature and relative humidity as driving potentials,based on Fick’s law,Darcy’s Law,and energy conservation law,as well as considering the heat and moisture exchange between the wall surface and the environment,the coupled heat and moisture transfer mathematical model of the earthen building wall and indoor air heat and moisture balance model are established.The rationality and accuracy of the model are verified by using analytical solutions and experimental data.The influence of hygrothermal parameters on one-dimensional wall heat transfer and moisture transfer on two-dimensional corner heat transfer is calculated and analyzed.Whether the moisture transfer is considered or whether the hygrothermal parameters of the wall material are constant has little influence on the temperature of the internal surface of the wall,but a significant influence on the heat transfer,especially under high temperature and high humidity conditions.Under different working conditions,the total heat flux and latent heat flux of the internal surface of the wall with constant hygrothermal parameters are higher than the function condition,and the maximum average error is 8.42% and 9.93%,respectively.In the outdoor high-temperature condition at the constant boundary,when the outdoor relative humidity is30%-95%,the total heat transfer on the internal surface of the corner increases by 69.63%-75.89% compared with the simple heat transfer condition,respectively,and increases by more than 56% in the outdoor low-temperature condition.At the periodic boundary,the heat transfer on the internal surface of the corner under low humidity conditions increased by 65.26% on average compared with that under simple heat transfer conditions,and the value was 65.66%under high humidity conditions.The hygrothermal state of the building wall affects the indoor hygrothermal environment.The influence of the moisture transfer state of earthen building walls on internal surface heat exchange and indoor hygrothermal environment is discussed.In the case of wall moisture absorption and discharge,constant hygrothermal parameters increase the total annual heat transfer by 4.04% but have little effect on indoor temperature and humidity.Earthen wall has an excellent ability for moisture regulation.Ignoring the absorption and release of moisture from the wall in heat and humidity calculation will underestimate the total heat transfer of the building wall.Meanwhile,increasing the ventilation frequency of the building will greatly increase the heat transfer of the wall and indoor temperature and humidity fluctuation.