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

Abstract

This paper proposes a methodology to assess fan energy savings when improving ductwork airtightness. This methodology builds on standard EN 16798-5-1:2017. 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 full scale ductwork built in a laboratory, the tool gives results in good agreement with measured energy savings (within 7 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.