A new airtightness test procedure has been developed for separating exterior envelope air leakage from interior partition leakage, when testing a single zone within a multi- zone building. Historically, envelope leakage from a single zone within a multi-zone building could only be measured if exact equalization was achieved of the pressure differentials across all interior partition surfaces using a masking blower(s). Experimentally, this has proven to be problematic with the result that the procedure is seldom used. The new technique, called the "Parallel Flow Airtightness Test" method (PFAT) permits partition leakage to be measured and subtracted from the total leakage of the test zone thereby allowing the exterior envelope leakage to be isolated and quantified. However, instead of requiring exact equalization of the interior partition pressure differentials, the new technique only requires that they be modified from their original values. Experimentally, this is a much easier condition to achieve and offers significant advantages to practitioners. As part of this thesis, the PFAT test procedure was proposed, validated in a series of laboratory trials and then applied to three different buildings to assess its practicality under real-world conditions. Using the results of the laboratory and field work, guidelines were then developed for applying the methodology to other structures. Under laboratory conditions (with no wind or indoor-to-outdoor pressure differentials to account for), the PFAT method was capable of measuring the exterior envelope air leakage with a maximum error of about 2% at 75 Pa, when a second blower was used to modify the pressure regimes in the adjacent, buffer zone. When the pressure regimes in the buffer zone were modified by simply sealing or unsealing a duct to the buffer zone, the accuracy of the procedure degraded significantly, producing errors of up to 26%. The field trials were then carried out on three multi-zone buildings in Winnipeg. From these trials it was concluded that the procedure seems well suited to field work and offers advantages, in terms of time and equipment, over the traditional pressure-masking technique. However, greater skill and better planning are required relative to that needed for a conventional, single-zone airtightness test. Overall, it was concluded that for many applications the PFAT method provides a workable method of separating interior partition air leakage from exterior envelope building
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