Study On The Characteristics Of Coupled Heat Air And Moisture Transfer In Building Walls In Cold Area

With the development of urbanization,the amount of high-rise buildings are increasing.The indoor and outdoor pressure difference caused by wind pressure,hot pressure and other factors is large.Air infiltration plays an important role in building energy saving,moisture-proof and mildew proof.Therefore,it is urgent to study the characteristics of coupled heat,air and moisture transfer in building envelopes.In this paper,a coupled heat,air and moisture transfer model is established to investigate and analyze the influence of indoor and outdoor pressure difference on hygrothermal characteristics of building envelopes by the method of theoretical analysis.The built model is solved by COMSOL Multiphysics~?multiphysics simulation software.By theoretical analysis and numerical simulation,the characteristics of coupled heat,air and moisture transfer in building envelopes have been studied,and the condensation risk assessment of building envelopes has been carried out.The main conclusions are as follows:(1)Considering the factors of air infiltration,gas-liquid phase transition and moisture transfer,taking relative humidity and temperature as driving forces,a coupled heat,air and moisture transfer model is established based on the law of conservation of energy and law of conservation of mass.The coefficients of the established model are simple and easy to determine and easy to solve.(2)The Poisson equation module and coefficient type partial differential equation module in COMSOL Multiphysics~?are used to solve the coupled heat,air and moisture transfer model.By comparing the results of the model solution with that of physical tests,the results of the temperature and relative humidity obtained by the solution are in good agreement with the results of the physical test,which verifies the reliability of the model built and the correctness of the solution method.(3)The model is used to numerically solve a 5-year numerical simulation of the coupled heat,humidity and air transfer of the walls on the windward and leeward surfaces of different building heights,revealing the hygrothermal characteristics of the walls under different indoor and outdoor pressure differences.The results show that in cold area city Xuzhou,the leeward wall is more humid in winter,while in summer,the windward wall is more humid.Meanwhile,the windward and leeward surfaces also affect the time it takes for the building wall to enter the normal stage.For the wall on the windward face,the time to reach the normal stage is shorter.(4)In this paper,the condensation risk assessment of different positions of building wall in Xuzhou in cold zone is carried out with the prerequisites of different air infiltration conditions are considered.The results show that air infiltration has a greate impact on risk of condensation in wall.Compared with normal stage,the impact of air infiltration in initial stage of the wall is more obvious.The risk of mold growth in different locations is different.The risk of condensation in wall is related to the hygrothermal transfer performance parameters of the materials in different location.Moreover,air infiltration in high-rise buildings will increase the risk of condensation in wall.There are 80 figures,16 tables and 113 references in the paper.