Research On Coupled Heat And Moisture Transfer Into External Wall Insulation Systems In Cold Area

Building energy consumption accounts for about 30% of the total social energy consumption in China.The heat loss of the external wall accounts for a large proportion of building energy consumption.How to improve the wall insulation performance and reduce the external wall heat loss is the key to develop energy-saving buildings.It is important to study the effect of heat and moisture transmission situation on insulation performance in external wall insulation system,which is the most widely used form of wall insulation in China.Water vapor is easy to condense and freeze due to severe indoor and outdoor environmental temperature difference that affect the wall insulation performance seriously.Analyzing the heat and moisture transfer characteristics of external wall insulation system in cold area is important to the correct wall thermal calculation,the improvement of wall insulation performance and indoor air quality as well as providing theoretical guidance for the practical engineering application.Based on Whitaker's volume average method,the mathematical model of coupled heat and moisture transfer using temperature and moisture gradient as driving forces was proposed.The accuracy of treatment of heat and moisture transfer at the interface of multilayer structure was verified by building the heat and moisture transfer experimental platform for multilayer envelope structure.The accuracy of heat and moisture transfer in porous media under ice condition was verified by the experiments of porous media in the published literature.The heat and moisture transfer characteristics of external wall insulation system in Harbin was studied,the difference of heat and moisture transfer characteristics under different external wall insulation system was investigated,and the influence of air layer,vapor barrier on the moisture content,freezing content,temperature,thermal resistance and heat transfer coefficient of external wall insulation system was analyzed.The lightweight concrete insulation system has less moisture content and good thermal insulation performance comparing with cast-in-place concrete insulation system.But the insulation layer of lightweight concrete insulation system has a high degree of moisture,which has a great influence on the heat transfer coefficient of the insulation system in heating period.The installation of the air layer can improve the overall temperature of the insulation layer,which is beneficial to alleviate the damp of insulation layer.Although the installation of vapor barrier layer can avoid insulation damp,but it will make the concrete layer with high moisture content.The high moisture content will destroy the internal structure of the wall and breed mold.The mold makes the indoor air quality worse.Considering the influence of moisture content inside the building materials,the thickness of the insulation layer satisfying the design limit is 149 mm and 124 mm respectively when the 240 mm thick cast-in-place concrete and 240 mm lightweight concrete are used as the basement wall in Harbin.