Research On Coupled Heat And Moisture Transfer Characteristics Of External Walls In Hot And Humid Climate

In hot and humid climate of south China,the heat and moisture transfer through wall has an important impact on the hygrothermal performance of building envelope, energy consumption and indoor environment.Since wall materials are porous media, and it is very complex that analysis moisture transfer in porous media,architects are more dependent on experience in the design of building envelope.For providing practical methods and empirical data to guide further research and engineering practice,experiments were conducted to analyze coupled heat and moisture transfer in external walls in South China.An experimental method was developed to test heat and moisture transfer through multilayer wall.Take cement mortar-red brick-cement plaster multilayer wall as an example,the temperature and relative humidity was measured in the external walls of an air-conditioned room in Changsha during January and July.The moisture accumulation and transfer within the walls exposed to hot and humid climate was also analyzed.Diverse internal wall surface materials was used to discuss the effect of different internal wall treatments on the hygrothermal performance of multilayer wall. The solar radiation of sunny and rainy days was measured.The changes of temperature and humidity inside walls under different climate conditions was compared and the effect of solar radiation on the distribution of temperature and humidity was analyzed.The experimental results of heat and moisture transfer inside walls indicate that:(1)The temperature and humidity at the interface between the cement mortar and red brick were seriously affected by the variation of outdoor temperature and humidity, the temperature and humidity at the interface between the red brick and cement plaster had small changes,they were affected by the variation of indoor temperature and humidity.(2)In summer,the temperature and humidity at the interfaces of the wall with foamed plastic wallpaper were generally higher than those of the wall without treatment.(3)In winter,the temperature at the interfaces of two walls was basically the same,but humidity at the interfaces of the wall without treatment were slightly higher than that of the wall with foamed plastic wallpaper. (4)Rainy day climate had a great influence on the moisture content in the wall, this can cause to relative humidity at the interface between the cement mortar and red brick close to saturation for a long-term.(5)The relative humidity of the interface between the cement mortar and red brick was likely to reach saturation in summer and winter during the period of air-conditioning,it was higher than 80 percent for a long-term,this can easy to trigger the growth of mold.(6)At the same time,the temperature and humidity inside the wall was coupled strongly,and solar radiation intensity had a great impact on the distribution of temperature and humidity inside the wall.In order to verify the experimental results,based on the heat and moisture transfer through porous media,a 1-D transient hygrothermal model for multilayer wall was established by using air humidity ratio in wall and temperature as the driving potentials was used to predict temperature and humidity distribution inside the wall. Considered the role of solar radiation on the external surface,the measured global solar radiation was decomposed into heat gains on different direction wall surfaces. The solution for the governing equations was obtained by implementing the finite-difference scheme,and the experimental results were compared with the prediction of the model.It shows that the prediction results have good agreement with the experimental results.The maximum deviation of temperature between model prediction and experimental testing is about 3.3K,and average deviation is about 0.5K.The maximum error of air humidity ratio between model prediction and experimental testing is about 9%,and average error is about 4%.