Study On Coupled Heat And Moisture Transfer Characteristics For Building Envelope In Hot And Humid Climate

The heat and moisture transfer has an important impact on building structure?energy consumption and indoor thermal and humidity environment.Based on the heat and mass transfer through porous media,and according to Fick law?Darcy law?Fourier law and the law of conservation of mass and energy,with the temperature and relative humidity as the driving potential,a coupled heat and moisture transfer model was proposed.Using a multi-physical field software COMSOL Multiphysics to solve the equations.Establishing the experimental platform of heat and moisture transfer through building envelope,taking red brick and aerated concrete wall in Nanchang as an example.The distribution of temperature and relative humidity were measured.Using the temperature and humidity sensor to test the indoor and outdoor temperature and humidity,as its boundary conditions.Using the coupled heat and moisture transfer model established in this dissertation to simulate.The simulation results were compared with the experiment test results.The four kinds of building enclosed structures characteristics of heat and moisture at actual weather conditions were analyzed by using the coupled heat and moisture transfer model,which are red brick wall?aerated concrete wall?plaster board –glass fiber –brick wall?new timber structure wall.Finally,four kinds of wall are sorted of good and bad by analytic hierarchy process,using the heat transfer rate?the assessment of mold growth risk?indoor air condensation critical state and economical efficiency as evaluating indicator.Through computational analysis,the weight coefficient of the four kinds of building enclosed structures respectively are 0.0573?0.4215?0.1489?0.3723.The maximum weight coefficient is the optimal building enclosed structures,so the comprehensive performance of aerated concrete wall is the best in hot and humid climate.Taking light wall and red brick wall as examples,the coupled heat and moisture transfer model is the model 1.Based on the model 1,assuming that the temperature gradient of moisture transmission equation is zero for model 2,The influence of temperature on the heat and moisture transfer of the wall was analyzed.And the results show that: regardless of the temperature gradient on the moisture transfer,it has little effect on the total heat load of the wall,but increases indoor humidity load.The light wall have better performance on the thermal insulation and moisture.But the indoor side have high relative humidity,so it is easy to cause moisture accumulation and promote mold.