Rationale for measuring duct leakage flows in large commercial buildings

Industry-wide methods of assessing duct leakage are based on duct pressurization tests, and focus on highpressure ducts. Even though low pressure ducts can be a large fraction of the system and tend to be leaky, few guidelines or construction specifications require testing these ducts. We report here on the measured leakage flows from ten large commercial duct systems at operating conditions: three had low leakage (less than 5% of duct inlet flow), and seven had substantial leakage (9 to 26%). By comparing these flows with leakage flows estimated using the industry method, we show that the latter method by itself is not a reliable indicator of wholesystem leakage flow, and that leakage flows need to be measured.