Field and Laboratory Evaluation of a New Ramping Techniques for Duct Leakage Testing
The DeltaQ duct leakage test has been developed over the past several years as an alternative to duct pressurization testing. A new ramping technique for obtaining the measured data has been developed in order to increase resolution at low envelope pressures and to make the test quicker and easier to perform. This study performed laboratory and field testing to investigate the bias and precision of the ramping technique and to determine test limits and recommendations for good practice. The laboratory testing compared the DeltaQ testing results to known measured leakage on a specially built tight duct system with known added leaks to evaluate potential biases and showed that the biases for the ramping test are typically less then 1% of system blower flow, with a range of zero to 1.5% of system blower flow. Additional pressurization tests were performed in the laboratory and showed that 0.1 in. water (25 Pa) pressurization tests have about 2 to 2.5 times the uncertainty bias for an individual test compared to DeltaQ. Correction factors to account for the pressure offset on the building envelope due to leakage imbalances and the change in duct static pressures due to duct leakage were found to be effective at reducing high leakage airflow over-predictions by reducing average flows by 10 cfm (5 L/s). The field testing used repeated tests in individual houses to examine repeatability and precision uncertainty. The experiences from field testing have shown that ramping is more time efficient and time savings are about 10 to 15 minutes and that the repeatability uncertainty is 1% of the 50 Pa (0.2 in. water) envelope leakage flow. Field tests to determine suitability for confirming zero duct leakage have shown that the same repeatability uncertainty can also be applied to the estimation of zero duct leakage. More houses need to be field tested for repeatability to confirm the finding that envelope leakage dominates over wind induced pressure fluctuations.
Year of Publication
Building Technology and Urban Systems Division, Residential Building Systems, Whole Building Systems Department