Impact of ductwork airtightness on fan energy use: calculation model and test case

This paper proposes a methodology to assess fan energy use savings when improving ductwork airtightness. This methodology is based on new standard FprEN 16798-5-1:2016. Unlike the classical "cube law", it considers pressure drops at air terminal devices separately from the pressure drops in the rest of the system. The calculation tool based on this methodology: a) gives the fan energy use before and after airtightness improvements with various inputs depending on the initial state; b) indicates whether or not the required airflow rates are met at the air terminal devices; c) gives a range of energy savings assuming on the one hand perfect fan adjustment, no errors in input data and constant fan efficiency, and on the other hand, safe-side estimates of deviations from these assumptions.
Using experimental data from an earlier study on a scale 1 ductwork built in a laboratory, the tool gives results in good agreement with measured energy savings. The deviation without pressure adjustment between experimental and theoretical savings lies in the region of 5 percentage points. With ideal pressure adjustment and when required airflow rates were met before tightening, the maximum fan energy savings by tightening the ductwork from 1.5 times Class A to Class C reaches 51% according to the tool versus 46% according to measurement data.