Measurement Of The Thermal And Hygric Properties Of Porous Building Materials And Analysis On Moisture Transfer For Walls

Abstract:With the development of society,the proportion of building energy consumption in total energy consumption is increasing in China,so the requirement of building energy conservation is becoming higher and higher.Mastering the heat and moisture transfer characteristics of multi-layer building wall is an important way to reduce building energy consumption.Understanding the wet physical properties of building materials is the primary basis.Based on the spherical absorption method for measuring the gas diffusion coefficient of porous media,an experimental platform for measuring the water vapor diffusion coefficient of building materials is set up.It is found that the spherical absorption method is suitable for measuring the water vapor diffusion coefficient of porous building materials,and has the advantages of short measuring time and accurate measuring results.In the data processing,the calculation of the water vapor diffusion coefficient using the half-time method is more accurate than the calculation using the moment method,but the uncertainty calculated by the half-time method is 14%,and the moment method is 6.1%.Based on the spherical absorption method,the water vapor diffusion coefficients of thermal insulation mortar and aerated concrete were measured at different relative humidity.It was found that the water vapor diffusion coefficients increased gradually between 45%RH and 80%RH,while in higher humidity,the existence and increase of liquid water reduced the water vapor diffusion channels.The water vapor diffusion coefficient of aerated concrete was measured at different temperatures.It was found that the water vapor diffusion coefficient increased with the increase of temperature in the range of 50%RH-70%RH and 5?-35?.According to the measured data,the formula of water vapor diffusion coefficient of aerated concrete changing with temperature and relative humidity is fitted,R~2 is 0.97.Based on Hot Disk thermal constant analyzer,the thermal conductivity of aerated concrete,gypsum,anticorrosive wood and carbonized wood under six different moisture contents were measured.It was found that the thermal conductivity of these four materials increased by 13.6%,35.9%,43.3%and 34.6%respectively after saturation in 90%RH.This shows that the change of moisture content has a great influence on the thermal conductivity,and the influence of moisture content should be considered in thermal design.A heat-moisture coupled transfer model is established and simplified based on COMSOL Multiphysics.The multi-layer wall with the structure of building gypsum-insulation mortar-aerated concrete-insulation mortar was fabricated.The heat and moisture coupling transfer test bench of the multi-layer wall was built.The unidirectional transfer experiment and the bidirectional transfer experiment were carried out.The model was verified by monitoring the temperature and humidity distribution in the wall.It is found that the maximum deviation between the simulated results and the experimental results is 12.61%and the average deviation is 4.78%in one-way transmission.The maximum deviation between the simulated results and the experimental results is 11.35%and the average deviation is 4.24%in two-way transmission.It is shown that the model can predict the temperature and humidity distribution of multi-storey walls under the influence of indoor and outdoor environment accurately.The wall of the six cities of Hangzhou,Chongqing,Guangzhou,Beijing,Qingdao and Lanzhou was subjected to a one-year heat-moisture coupling calculation using COMSOL Multiphysics,and the mold growth time was predicted.It is concluded that Guangzhou,which belongs to the hot summer and cold winter regions,and Guangzhou,in the hot summer and warm winter regions,have a high risk of mold growth,and buildings need to take moisture-proof measures;Beijing,Qingdao and Lanzhou,which belong to the cold regions,have different climates.There is a big difference in the demand for building moisture protection measures,which also shows that the current temperature-based building climate zone can no longer meet the current needs of people's indoor comfort.