Recovered-heat fuel-cost credit calculator

The usable recovered heat displaces boiler fuel after dividing by boiler efficiency and gas heat content.

Units

S_{\text{heat}} = \frac{P \times H \times a \times q_{\text{rec}} \times f_{\text{use}} \times c_{g}}{\eta_{\text{boiler}} \times B_{g}}

Calculator

Enter the values you know and leave one box empty. Calculate finds the empty one, the result or any input.

Given

S_{\text{heat}} = \frac{350 \times 5800 \times 0.92 \times 4100 \times 0.7 \times 10}{0.84 \times 1{,}000{,}000} \approx 63{,}810

Symbol	Meaning	Unit
$S_{\text{heat}}$	annual displaced boiler fuel cost	$/yr
$P$	DG output	kW
$H$	yearly scheduled operating hours	h/yr
$a$	availability	fraction
$q_{\text{rec}}$	recoverable heat per generated electricity	Btu/kWh
$f_{\text{use}}$	fraction of recovered heat actually used	fraction
$c_{g}$	gas price	$/Mcf
$\eta_{\text{boiler}}$	displaced boiler efficiency	fraction
$B_{g}$	gas heat content; case assumes 10⁶	Btu/Mcf

Symbol	Meaning	Unit
$S_{\text{heat}}$	annual displaced boiler fuel cost	$/yr
$P$	DG output	kW
$H$	yearly scheduled operating hours	h/yr
$a$	availability	fraction
$q_{\text{rec}}$	recoverable heat per generated electricity	kJ/kWh
$f_{\text{use}}$	fraction of recovered heat actually used	fraction
$c_{g}$	gas price	$/m³
$\eta_{\text{boiler}}$	displaced boiler efficiency	fraction
$B_{g}$	gas heat content	kJ/m³

Results are estimates for study and screening. Check the inputs, units and assumptions before you use them for design, billing or contract decisions.