The recovered heat is calculated using the heat exchanger efficiency (effectiveness), minimum heat capacity rate, and temperature difference between the flue gas inlet and feedwater inlet. This represents the actual heat transferred from the flue gas to the feedwater.

\begin{equation}\label{eq:water-heating-flue-recovered-heat} Q_{rec} = \eta_{hx} \cdot \dot{C}_{min} \cdot (T_{flue,in} - T_{fw,in})\end{equation}

Symbols

\(Q_{rec}\)	Recovered heat \([\unit{ \kilo\joule\per\hour}]\)
\(\eta_{hx}\)	Heat exchanger efficiency (effectiveness) \([\unit{ \unitless}]\)
\(\dot{C}_{min}\)	Minimum heat capacity rate \([\unit{ \kilo\joule\per\hour\kelvin}]\)
\(T_{flue,in}\)	Flue gas inlet temperature \([\unit{ \kelvin}]\)
\(T_{fw,in}\)	Feedwater inlet temperature \([\unit{ \kelvin}]\)