Inside a ductwork a flow rate undergoes pressure drop due to friction and dynamic losses. Numerical models  were set and experiments were conducted  to determine the impact of those pressure losses on the result of a ductwork airtightness test. It has been shown that, for airtight ductwork (class C) the impact of pressure losses on the measured flow rate is expected to be very small. Nevertheless, for very leaky ductwork it would be good practice to determine (through calculation described in ) the maximal length to be tested (distance between the measuring device and the farthest end of the ductwork) or to check in various locations the homogeneity of the pressure.
 Berthault S. & Leprince V., 2019. Reliability of ductwork airtightness measurement: impact of pressure drop and leakage repartition on the test result . 40th AIVC Conference “From Energy crisis to sustainable indoor climate – 40 years of AIVC", Ghent, Belgium, 15-16 October 2019
 Berthault S., Boithias F., & Leprince V., 2014. Ductwork airtightness: reliability of measurements and impact on ventilation flowrate and fan energy consumption. 35th AIVC Conference "Ventilation and airtightness in transforming the building stock to high performance", Poznań, Poland, 24-25 September 2014
Posted in: Ductwork airtightness