Field comparison of alternative techniques for measuring air distribution system leakage.

ASTM has recently standardized a methodology for measuring the leakage of residential air distribution systems to unconditioned zones. The standard includes two alternative leakage measurement techniques, one of which requires only a blower door, whereas the second technique requires a flowcapture 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, are examined. A key issue that is addressed in this paper 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 be negatively biased by 30-50% if the duct pressure was not incorporated into the measurements and analyses as is specified in the standard. Similarly, it is shown that supply leakage measurements with the flow-capture-hood technique would be negatively biased by 33% if the envelope pressure differential was used instead of the duct pressure differential.