Performance of duct leakage measurement techniques in estimating duct efficiency: Comparison to measured results

Duct leakage is recognized as a major source of energy losses in residential buildings, and is one of the most important parameters for estimating duct efficiency. However, quantifying duct leakage has proven to be extremely difficult. Several methods of estimating duct leakage have been proposed. This paper focuses on the predictions of supply duct leakage from a study in which duct efficiency estimates were made using a variety of duct leakage measurement techniques, and were compared to measured efficiencies using the coheat test methodology. The leakage measurement methods tested in this study include the duct pressurization test and house pressure test that are found in the current version of ASHRAE Standard 152P, as well as three other methods: the supply-blocked house pressure test, where the supply registers are partially blocked instead of the return grilles; the "hybrid test", which combines a total duct system pressurization test with a portion of the house pressure test; and the "nulling test", which uses a calibrated fan to counteract the pressure change across the envelope due to duct leakage. The two forms of the house pressure test showed a large amount of scatter. The duct pressurization test showed significantly less scatter, but is more time-consuming. The performance of the hybrid test fell between the house pressure test and duct pressurization test. Though only tested in a few cases, the hulling test performed well, providing cause for optimism and further study. The comparisons of estimated efficiencies using these methods to measured efficiencies provide insight into the importance of accurate measurement of duct leakage, as well as the ability of each measurement method to provide good predictions of duct efficiency. The results have implications for ASHRAE Standard 152P and raise the possibility that newer techniques may be improvements over the methods in the standard.