There exist a number of national standards and a draft international standard for the fan pressurization method for measuring air leakage. Although the standardized methods in principle are the same, the way of interpreting and presenting the results is different.
In previous studies, houses that have a relatively large leakage area at a low pressure difference (4 to 10 Pa) still can seem comparatively airtight at a high pressure difference (50 Pa). This fact is a consequence of differences in the flow exponent in the power-law equation, which is the normal equation used to fit to the data points, and can be a source of error when trying to compare the relative airtightness of houses. Extrapolating results from high pressure differences to low pressures, which are out of the measured range, can thus result in substantial errors. Air leakage testing of windows normally starts at 50 Pa, which should be accounted for when trying to use these results as inputs in network air infiltration models. Measurement results on low pressure air leakage are discussed in the paper and compared with high pressure air leakage.
Pressurization test data from 105 tests in one house at the Alberta Home Heating Research Facility are used for the study. The tests were made automatically over a seven-month period in low wind conditions. A wide range of pressure differences were tested and the results cover the test specifications for most standards. In addition to comparing standards, these tests were used to measure seasonal effects on air leakage in a wood-frame house with a plastic film air/vapor barrier.
The results show some significant differences between the standards, and also a variation with month of test, indicating a seasonal variation in air leakage.