Study On The Heat And Moisture Transfer Characteristics Of The Building Corner With Different Column Structures

Accurate calculation of palisade structure heat transfer is the basis of the HVAC system design and building energy consumption analysis,due to the thermal bridge effect,the amount of heat loss through the corner of the building cannot be ignored.At present,most of the researches on the building outer corner are based on the simple heat transfer theory and lack the representation of the moisture transfer path.However,under the influence of multidimensional effect,the effect between the heat and moisture coupling is amplified.If the moisture transfer is ignored,it will have an important impact on the calculation results of the heat loss of buildings.Therefore,studying the multi-dimensional heat-moisture coupling transfer characteristics of building outer corner and determining the effect of moisture transfer on the heat transfer characteristics of building outer corner are the key to accurately calculate the overall heat transfer loss of buildings.Based on this,through the summary of the atlas of architectural design standards and the existing forms of the outer corner of the building,three different forms of building outer corner are summarized in this paper: the pure masonry outer corner,including the outer corner of the constructional column,including the outer corner of the frame column.Based on the analysis of the heat and moisture transfer mechanism of the envelope structure,the perfect mathematical model of the heat and moisture coupling transfer is established,and the mathematical equation is solved by using the finite element software COMSOL Multiphysics.The difference of the inner surface temperature and heat flow in the outer corner of different column structures under different boundary conditions with and without moisture transfer are analyzed,and the influence of moisture transfer on the heat transfer characteristics of the building outer corner are obtained.This study first takes the pure brick masonry building outer corner as the research object,the influence of outdoor relative humidity changes and different external wall insulation systems on the heat and moisture characteristics of the building outer corner are qualitatively discussed and the evaluation indexes of thermal bridge effect are put forward,such as the influence area of thermal bridge and the loss rate of heat flow,to analyze the relations between corner moisture transmission and the influence of thermal bridge effect.It is found that: when the indoor temperature and humidity and outdoor temperature are constant,the higher the outdoor relative humidity,the greater the influence of moisture transfer on the temperature and heat flow of the outer wall;The thicker the insulation layer is,the less obvious the moisture transfer phenomenon is.Compared with the three types of heat preservation,the external heat preservation structure is more conducive to maintaining the indoor temperature stability,but it is more affected by the moisture transfer than the internal heat preservation structure.After considering the moisture transfer,the influence area length and heat loss rate of the corner both increase,indicating that the presence of moisture transfer will aggravate the heat bridge effect of the outer corner.By comparing the numerical results of the outer corner under the condition of considering and not considering the moisture transfer,get the following conclusions:(1)After considering the moisture,through the outer corner of the total quantity of heat to increase,in high temperature and low humidity,high temperature and high humidity,low temperature and humidity,low temperature and humidity conditions of heat flow increase amplitude,respectively,the main wall materials for brick masonry: pure masonry outer corner: 4.2%,21%,7.1%,11.7%;Including the outer corner of constructional column: 5.9%,25.7%,8.9%,11.7%;Including frame column outside the corner: 6.8%,24.9%,9.5%,14.2%;The main wall material is aerated concrete masonry: including the outer corner of constructional column: 6.1%,37.8%,11.8%,14.3%;Including frame column outside the corner: 7.1%,32.7%,11%,14.8%.(2)Compared with the outer corner structure of brick masonry,when the main wall material is aerated concrete,the corner structure has better thermal insulation performance,but the thermal bridge effect and the influence of moisture transfer are greater;The influence of thermal bridge effect is increased when the angle column material is different from the main wall material.The greater the width of corner column,the greater the heat loss rate in the corner,and the less the influence of the angle column on the temperature and heat flux of the main wall.(3)The mean heat transfer coefficient of building outer corner increases with the consideration of moisture transfer,and the higher the outdoor temperature and relative humidity are,the higher the correction rate of the mean heat transfer coefficient in the corner is.Taking Wuhan summer as an example,plain brick masonry,including constructional column brick masonry,including frame column brick masonry,including constructional column aerated concrete masonry,including frame column aerated concrete masonry five outside corner structure after considering the moisture correction rate is respectively: 12%,12.8%,15.5%,26.7%,23.8%.Through the above theoretical analysis and numerical simulation research,the heat and moisture coupling transfer characteristics of the building outer corner with different corner column structures are obtained,and the effect of moisture transfer on the heat transfer characteristics of the building outer corner is obtained.At the same time,the mean heat transfer coefficient correction rate of the external wall corners of major cities in the country are obtained,provide a reference for practical engineering application.