Reducing Measurement Uncertainties in Duct Leakage Testing

J W. Andrews, Brookhaven National Laboratory

Keywords

Abstract

Air leakage from residential ducts accounts, typically, for about half ofthe energy losses in these systems. For this reason, ASHRAE Standard 1 52P requires that this leakage be measured. A major problem in duct leakage testing is the relatively large uncertainty in the measured values, using currently available methods. This paperpresents a general approachto reducing this uncertainty, based on the use ofmore datathanis strictly required to calculate the leakage values. This over-constrains the solution. Where the data are internally consistent, the error bar is reduced. In cases where the data are internally inconsistent (which is not rare) the error bar is not reduced significantly, but the process does produce a result that is more credible than any answer obtained from a lesser data set. In addition to reducing measurement uncertainties, the method can also be usedto validate duct leakage testmethodsthat arenot overconstrained. The method is applied to published field data from projects whose aim was to validate ASHRAE Standard 152. A newduct leakage test that uses a greatly over-constrained data set is also discussed.