Dynamic Experimental Study On Thermal Performance For External Building Envelope Of New Building

At present,the energy and building problem has been a major problem faced by countries all over the world,building energy efficiency is an important aspect of saving energy.The heat transfer coefficient value of building envelope is an important factor influencing building energy consumption.Building envelope materials are usually porous media,building envelope of the new building are usually wet unsaturated porous media.The complex heat and mass transfer process will affect its thermal insulation performance.It should be considered in practical engineering problems that the influence of moisture saturation on the transfer coefficient.In this paper,the dynamic change of heat transfer coefficient of new building envelope is studied experimentally.In the situ experiment house built by this research group,installing the temperature and moisture system and the heat flow detection system.Tracking detection of the heat and wet state;using heat flow meter method to detect the comprehensive heat transfer coefficient of building envelope regularly.In order to detect the moisture saturation of the building envelope,the humidity sensor buried in the building envelope is calibrated.In regard to the change of the comprehensive heat transfer coefficient of the external building envelope.The comprehensive heat transfer coefficient of the external building envelope was detected by the method of heat flow meter,t his paper uses the arithmetic average method and dynamic method to calculate the experimental comprehensive heat transfer coefficient of the building envelope.The results show that the comprehensive heat transfer coefficient of the building envelope rose first and line declined gradually.the results of the dynamic method were calculated:After the building finished 551 days,the comprehensive heat transfer coefficient of the north reinforced concrete wall is 0.3394W/m~2·K,which is 1.0019 times the theoretical value.The experimental comprehensive heat transfer coefficient of the northern gas concrete wall is 0.3537W/m~2·K,which is 1.0441 times the theoretical value.The composite heat transfer coefficient of the roof is 0.4146W/m~2·K,which is 1.224 times the theoretical value,they are all larger than the theoretical value.In regard to the change of the moisture saturatio n of the external building envelope.Based on the analysis of testing data,the building complete 26 days to 410 days,the moisture saturation of the external building envelope presents the first drop(completed in 26 days to 259 days)after rising(completed in 260 days to 260 days).As a result of the outdoor air humidity ratio of the external building envelope moisture saturation has a lag,the influence of moisture saturation changes and the changes of moisture content of outdoor air present opposite symmetrical curve relationship.Analysis and Suggestions: The comprehensive heat transfer coefficient of external building envelope of new building came first 50 days after brief rise again in the process of gradual decline,this is because the early experime nts result of EPS thermal insulation layer of palisade structure are affected with damp.Therefore,the test of heat transfer coefficient should not be carried out within 50 days of construction.In order to avoid the effect of direct sun radiation on the heat transfer performance of the containment structure,it is reasonable to test the wall in the north.In order to ensure the temperature difference between inside and outside surface is more than 10 ?,the actual test is best done in the outdoor temperature is low season.In the test of comprehensive heat transfer coefficient by heat flow meter,the heat transfer coefficient can be affected by the fluctuation of outdoor temperature.Respectively by arithmetic mean method and dynamic method to calculate the north reinforced concrete wall of every test experiment the integrated heat transfer coefficient and linear fitting,the results show that the dynamic method to calculate the linear correlation coefficient significantly greater than the arithmetic average method.So,in the case of outdoor temperature fluctuations,using dynamic method to calculate experimental integrated heat transfer coefficient of enclosure structure is more reliable than the arithmetic average method.