New transient pressurisation methode for measurements of airtightness in building envelope components
Övrigt konferensbidrag, 2006
When the airtightness of a building is determined, fan pressurisation is generally used. The European Committee for Standardisation states that a pressurisation test should be performed according to a modified version of ISO 9972:1996, labelled EN 13829:2000 . According to this test method the air leakage should be measured for steady-state pressure differences in steps of no more than 10 Pa, ranging from 10 Pa to at least 50 Pa. Instead of measuring the air flow rate for different steady-state pressure differences, it is possible to pressurise an air volume to a prescribed pressure difference, seal the channel providing air and measure the declining pressure difference in the pressurised volume. By measuring the pressure decline in this pressurised air volume, from which air is leaking, it is possible to determine the air leakage rate. Mass balance and the gas law give that the air leakage rate is proportional to the time derivative of the pressure difference. The constants of proportionality turns out to depend on the size of the pressurised volume, the ambient pressure, the change in temperature in the bulk volume of the pressurised air and the stiffness of the structure enclosing the pressurised volume. The derived equation relating air leakage to pressure drop is given. Initial tests of the method have been performed. The derived, quite handy, equation shows good agreement with air leakage rates obtained with theoretical as well as standard steady-state methods.