The bag method estimates flow rate by measuring how long it takes to fill a known-volume bag with compressed air from a leak or equipment vent. Dividing the bag volume by the fill time (converted to minutes) gives the instantaneous flow rate in scfm. Annual consumption is then computed from the flow rate, operating hours.

\begin{equation}\label{eq:compressed-air-reduction-bag-flow-rate} Q_{bag} = \frac{V_{bag}}{t_{fill} / 60}\end{equation}

\begin{equation}\label{eq:compressed-air-reduction-bag-consumption} C = Q_{bag} \cdot t_{op} \cdot 60 \cdot n\end{equation}

Symbols

\(Q_{bag}\)	Estimated compressed airflow rate \([\unit{ \cubic\foot\per\minute}]\)
\(V_{bag}\)	Internal volume of the bag \([\unit{ \cubic\foot}]\)
\(t_{fill}\)	Time to fill the bag with compressed air \([\unit{ \second}]\)
\(60\)	Unit conversion factor (seconds per minute) \([\unit{ \second\per\minute}]\)
\(C\)	Annual compressed air consumption \([\unit{ \cubic\foot\per\year}]\)
\(t_{op}\)	Annual operating hours \([\unit{ \hour\per\year}]\)
\(n\)	Outer quantity multiplier (number of identical measures) \([\unit{ \unitless}]\)