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ASTM has recently standardized a methodology for measuring the leakage of residential air distribution systems to unconditioned zones [ASTM Test Method for Determining the External Air Leakage of Air Distribution Systems by Fan Pressurization (E 1554-93)]. The standard includes two alternative leakage measurement techniques. One technique requires only a blower door, whereas the second technique requires a flow-capture hood as well as a blower door. This paper reports on the results of field measurements in 30 houses using both measurement techniques, and analyzes the relative strengths and weaknesses of the two techniques. The repeatability of each of the techniques, as well as the comparability of the results from the two techniques, is examined. A key issue addressed is the importance of duct pressure measurements in each of the two techniques. Analyses show that the leakage measured with the blower-door-only technique would have been negatively biased by 30% to 50% if the duct pressure had not been incorporated into the measurements and analyses as specified in the standard. Similarly, it is shown that supply leakage measurements with the flow-capture-hood technique would have been negatively biased by 33% if the envelope pressure differential had been used instead of the duct pressure differential.
ducts, leakage, airtightness, fan pressurization, measurement, infiltration
Lawrence Berkeley Laboratory, Berkeley, CA