Experimental study on the pressure differential at which building air leakage should be measured

Air infiltration represents up to one third of the energy losses in a building. Air leakage is the parameter that has the biggest effect on air infiltration. Currently the Air Leakage Rate (ALR) is measured by means of a (de) pressurisation technique and is quoted at 50 Pa of pressure difference. Some research has shown that building air leakage occurs at low pressure differences, in the range of 1 -10 Pa. To get an ALR at low pressures, the pressurisation test result must be extrapolated; large uncertainty is created through this process. Other novel method (Pulse) measures the air leakage rate and quotes it at 4 Pa. This study aims to measure the pressure difference in four facades of a test house in Nottingham, United Kingdom. Differential pressure transducers measured indoor-outdoor pressure differences for a six-day period. Air leakage tests were also carried out with the wind speed, indoor and outdoor temperatures being monitored on site. Results showed that the majority of the pressure difference in the tested house occurred between 3.5 and 4.5 Pa even when high wind gusts (up to 9 m/s) were present. The distribution of the measured pressure differences follows a normal (Gaussian) distribution. The calculated mean pressure difference was close to 3 Pa, which agrees with authors saying that air leakage occurs in the range of 1 – 10 Pa under natural (environmental) conditions. This suggests that a technique that measures and quotes ALR at 4 Pa should deliver more representative results.