建筑外围护结构整体气密性能检测关键技术

建筑外围护结构整体气密性能是低能耗建筑的一项重要技术指标,但是我国尚未建立相关的测试标准和测试方法。在国外建筑外围护结构整体气密性能检测标准的基础上,通过大量工程测试应用实践,结合我国建筑发展特点和科学技术水平,研究提出我国建筑外围护结构整体气密性能检测中关键问题的解决方法,提高相关测试方法和测试数据的科学性与真实性,为今后我国建筑外围护结构整体气密性检测标准的编制和测试方法的应用提供参考和借鉴。

Key Technique in Determination of Air Permeability of Overall Building Envelope

The air permeability of overall building envelope is an important technical indicator of the low-energy buildings which could influence the heating or cooling load, indoor comfort and indoor air quality significantly.Recently, China has been promoting the exemplary construction of energy-efficient buildings such as green building, ultra-low energy building vigorously.Therefore, along with the completed acceptance of these buildings, the air permeability tests of overall building envelope will be a kind of important, scientific and precise work.Depending on the testing standard about the air permeability of overall building envelope abroad, through lots of application practices of energy-efficient building tests, combined with the architectural characteristics as well as the science and technology level in China, several solutions dealt with the key issue from different test steps have been carried out which incorporate equipment operation, measurement conditions, measurement preparation, measurement conditions, measurement method and detection of the leakage location.The improved authenticity and scientificity of the tested data and testing methods will provide useful reference for the standard compilation and testing method application for our country henceforth.Equipment operating: The air flow should be lower than the 70% of the fan rated air flow owning to the measuring principle limitation.Additionally, both the air temperature and barometric pressure should be measured.Moreover, considering with the influence from ambient temperature and relative humidity, the digital differential pressure meter generally select the air temperature from 0 ℃~48 ℃ and the relative humidity from 10%~90%RH.Measurement conditions confirmation: firstly, the testing range should be confirmed based on the air tightness layer of the building design.Artificial segmentation of the testing area resulted from the equipment air volume limitation is not allowed.Secondly, the testing time should be ascertained at two-key point, for detailed, the initial test should proceed after the air tightness layer blank construction of the building envelope while the second test should start after the total building construction which include decorate construction as well.Thirdly, the air permeability test of building envelope should pay attention on the limitation of environment condition.The surface wind speed of the primary tested building surroundings should be less than 3m/s.The product of the outdoor temperature and building altitude around the second tested building should be less than 250 m·K.Considering with the real architecture situation in China, the testing environment condition of the high-rise and super high-rise building could be extended to 6 m/s and 500 m·K.Measurement preparation: the measurement should be prepared based on the method 1 in ISO9972 rather than taking airtight measures artificially for better tested results.Next, a special area that respond to pressurization should exist inside the building.Meanwhile, all the doors inside the building should be opened.Furthermore, the blower doors with appropriate size are preferred for the low-rise and multistory buildings.As to the high-rise and super high-rise building, the blower doors should be installed primarily in the place where it is linked with hallway or closed to the atrium and staircase.Lastly, the connection arrangement of piezometric tube between indoor and outdoor should eliminate the influence from wind speed and temperature difference.Measurement method: firstly, there should be five measurement pressure differences at least during the test.The measurement pressure is supposed to involve 50Pa, thus the air leakage amount under 50 Pa needn't be calculated by fitting formula.Secondly, relative building parameters should be calculated through overall internal dimensions and construction as-built drawings.Lastly, the n50 of internal volume is usually regarded as the judging index while the qE50(q50)of the building envelope structure area is selected when the building volume is larger than 4000 m3.The detection of air leakage location: The subtraction method is suitable for the detection of air leakage location and qualitative check in large-scale area at preliminary stage.The cover method is appropriate for the buildings without other leakage testing equipment which need to observe the fan flow rate variation constantly.The infrared thermo viewer method needs a certain range of temperature differences(larger than 5 ℃) between indoor and outdoor which could replace the subtraction method.The common-used equipments of the smoking method include miniature smoke pen and large smoke generator.The smoke pen is used for confirming the detailed location of air leakage while the smoke generator is used for the outdoor air leakage test at large area.When it uses the air velocity meter method, the air leakage location will be ascertained quantitatively by the wind speed appeared on the air velocity meter.Nevertheless, the air leakage could not be avoided, to find out the reasonable air leakage amount from the place, more experience accumulation through plenty engineering practices is indispensable.Comprehensive analysis about the testing project, scientific measurement preparation, vigorous measuring method according to the correlative standards and accurate expression of the tested results constitute the key points of the air permeability test of overall building envelope.