Theoretical And Experimental Study In Coupling Transfer Of Thermal,Moisture,and Air In Wall

Concrete is the most popular building material,as well as a typical porous media.The heat property of the envelope is a determinant of the whole energy consumption,dewing will extensively cut down the thermal resistance of the envelope which will make the energy consumption very high.Heat bridge will also reduce part of the envelope's heat resistance.This article take combined heat,moisture and air transfer as research object,generalized some mathematical models like Luikov model,Lewis model and Philip & De Vries model.Water absorbing experiment is taken to concrete C20,C30 and C40,which would make sure the water absorbing property of them,as well as scanning electron microscope is fitted to the concretes,which would make sure the complexity of the pores.CHAMPS-BES is used to simulate the heat and moisture distribution in the normal wall,the wall of the basement and the wall in heat bridge.Through the experiment,concrete C20 absorbed the most water while concrete C30 absorbed the less,at the same time,the pores in concrete C20 is the most complex while that in concrete C30 is the less complex.The water absorbing property has nothing to do with the strength but the pores of the concrete.Through the simulation,take the downer corner of the balcony floor as point A,and the upper corner of the downer floor of the balcony as point B,the relative humidity in point A is always lower than that in point B,when the balcony is located 50% lower,the relative humidity of point A is lower than that in the normal balcony,while that of point B is hardly changed.When the relative humidity of the indoor air is higher than 80%,dewing would appear more or less in the structure and the liquid water will get together when 500 days passed,dewing would not happen when the relative humidity of the indoor air is 70%.Lower exchange coefficient for vapor diffusion may reduce the probability of dewing,the suddenly change of indoor air temperature may let the heat in the wall flows to the inner surface of it for a short time.The exchange coefficient for vapor diffusion is lower,the for the heat flow to recover is shorter,when the exchange coefficient for vapor diffusion is 1.5×10-8s/m the recovery speed of heat flow is the slowest.Higher exchange coefficient for vapor diffusion may make the change of water vapor pressure small when temperature is suddenly changed,and it takes shorter time to recover to balance.The inner face of a standard wall for residential building in Shenyang is in high relative humidity in most time of the year without dewing,the relative humidity in summer is the lowest,when it's 80%~85%.Using materials of bad water-absorbing performance and controlling relative humidity of the indoor air can reduce the probability of dewing and propagating of the moulds.The results of this paper may supply some reference for controlling of dewing and propagating of the moulds.