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Building air infiltration rate is required as an important input in the calculation of building heat loss. Tests to directly measure infiltration rates are complex and time-consuming to perform, and are therefore usually substituted with an airtightness test as a more efficient alternative. An empirical ratio, or sometimes an infiltration model, is then used to predict the building infiltration rate from the measured airtightness value. For instance, in the United Kingdom the building air permeability measured by a steady pressurisation test and reported at 50 Pa
(Q50) uses the so-called divide-by-20 rule to obtain the air infiltration rate. The blower door test, as a standard and widely accepted steady pressurisation method for measuring the building airtightness, takes the measurement in a range of high pressures (typically 10-60 Pa), which are regarded as being much higher than that experienced by buildings under natural conditions. Hence, an extrapolation is required and error could incur. The low-pressure Pulse technique has been developed to take measurements at low pressures (typically 1-10 Pa) directly and it therefore avoids the extrapolation process. However, it has been often asked how the test results given by the two different airtightness test methods compare with each other and how the Pulse test result can be used in the building energy assessment. A field trial study using the blower door, Pulse and tracer gas methods were carried out in over 100 dwellings to (tracer gas tests were conducted in 21 of them):
- identify the correlation between the test results given by the Pulse and blower door methods
- establish the correlation between the Pulse test results and infiltration rate to allow the infiltration rate to be predicted when the pulse test is carried out
The results showed that there is a strong correlation (a factor of 5.3) between measurements given by the blower door and Pulse methods and an initial Pulse-infiltration correction range (from 5 to 11) has been obtained.