Research On The Effect Of The Palisade Structure Moisture Transfer On The Indoor Thermal Environment And Air-conditioning Load

The building heat and cold load is the foundation of energy-saving analysis anddesign and operation control of HVAC system. The building load mainly depends onthe heat flux of palisade structure inner surface which has relation with heat andmoisture transfer process inside the structure and at the surface. At present, thecalculation software and design specification are mainly based on the heat transfertheory. There are many scholars have researched on the coupled heat and moisturetransfer inside the wall and moisture transfer in the air, but the effect of moisturetransfer inside the structure and at the surface on the load is rare reported. China’s vastterritory, hot wet climate diversity, ignore the palisade structure of moisture transfer isbound to be on the indoor thermal environment and building cooling and heat loadanalysis cause different degree of error.The existing load calculation method is difficult to reflect the influence of moisturetransfer on the load. Theory analysis, validation analysis, numerical calculation andfield test are used to research the influence of moisture transfer on the indoor thermalenvironment and building heat and cold load.Based on the analysis of heat and moisture transfer mechanism, the coupled heatand moisture transfer mathematical model for palisade structure and surface aredeveloped. The constant value of heat and mass transfer coefficient in previous researchis difficult to reflect the coefficient changes with the environment. In this paper, the heatand mass transfer coefficient changes with the temperature and relative humidity areobtained.The coefficient partial differential equations module in the COMSOL Multiphysics software is used to program and solve the coupled heat and moisture transfer equations.The difference of internal surface temperature and heat flux with taking the moisturetransfer into account or not under the various boundary conditions is calculated andanalyzed. The effect of moisture transfer on the heat transfer process is obtained. Theresults show: the reduce scope of the wall internal surface temperature with taking themoisture transfer into account, pine board wall:0.1℃~1.4℃, Concrete wall:0~0.2℃,Porous brick wall:0.1℃~0.7℃. The latent heat ratio in the total heat transfer amountfor the wall internal surface, pine board wall:12%~73%; Concrete wall:0~8%;Porous brick wall:9%~36%.Based on the effect of the moisture transfer on the heat transfer process, with thecalculating program for the coupled heat and moisture transfer, MATLAB is used toprogram and solve the hot wet environment equations for the whole room. The effect ofmoisture transfer on the wall internal surface temperature and the indoor thermalenvironment is analyzed. Considering the difference for the wall moisture content, thewall surface temperature and indoor thermal environment is field tested for4kinds ofdifferent buildings with different moisture content respectively. The effect of moisturetransfer on the indoor thermal environment is analyzed.The results revealed that: duringthe air-conditioning period in summer, the wall inner surface moisture transfer candecrease the internal surface temperature obviously, thereby lowering the averageradiation temperature. Under the conditions of the same thermal comfort, theair-conditioning load and the using time can be reduced. The absorption-desorptionprocess of the wall internal surface has significant effect on the indoor air relativehumidity and less effect on the indoor air temperature. Taking the moisture transfer intoaccount, the reduction for indoor air relative humidity, Guangzhou:5%, Xi’an:3%,Harbin:3%, Beijing:5%.For the buildings with air-conditioning during the day and natural ventilationduring the night in hot humid climate, the effect of the moisture transfer inside the walland at the surface on the indoor thermal environment and air-conditioning load isresearched with taking natural ventilation during the night into account. The resultsshow that: the ventilation rate has more significant impact on the indoor air relativehumidity and has less obvious effect on indoor air temperature. The total load is compared whether taking moisture transfer into account. When the night ventilation rateis5ACH, the reduction of the total load is about6%. However, when the nightventilation rate is5ACH, the increase of the total load is about20%. Therefore, thenight ventilation rate should be reasonable setting can effectively reduceair-conditioning load in hot humid climate.The difference of the hot humid climate characteristics is large in China. Theoutdoor air relative humidity of the coldest and hottest month for the typicalmeteorological year is collected. The air relative humidity is used to divide hot humidclimate zones and the humid zones are obtained in the winter and summer. Thecalculation method of building load with taking moisture into account is proposed. Thebuilding load correction coefficient is obtained for major cities. The building loadcalculation method and reference data are proposed for the accuracy of load calculationfor engineering.