Calculators › Renewables and on-site generation CHP primary-energy saving (PES) calculator
CHP primary-energy saving
Compare CHP fuel with separate generation fuel required for the same useful electrical and heat outputs, using stated reference efficiencies and one consistent fuel-energy basis; actual useful heat must have a load.
Units IP (US) SI (metric)
P E S = E el η grid + Q heat η boiler − F CHP E el η grid + Q heat η boiler × 100 \mathrm{PES} = \frac{\frac{E_{\text{el}}}{\eta_{\text{grid}}} + \frac{Q_{\text{heat}}}{\eta_{\text{boiler}}} - F_{\text{CHP}}}{\frac{E_{\text{el}}}{\eta_{\text{grid}}} + \frac{Q_{\text{heat}}}{\eta_{\text{boiler}}}} \times 100 PES = η grid E el + η boiler Q heat η grid E el + η boiler Q heat − F CHP × 100 P E S = E el η grid + Q heat η boiler − F CHP E el η grid + Q heat η boiler × 100 \mathrm{PES} = \frac{\frac{E_{\text{el}}}{\eta_{\text{grid}}} + \frac{Q_{\text{heat}}}{\eta_{\text{boiler}}} - F_{\text{CHP}}}{\frac{E_{\text{el}}}{\eta_{\text{grid}}} + \frac{Q_{\text{heat}}}{\eta_{\text{boiler}}}} \times 100 PES = η grid E el + η boiler Q heat η grid E el + η boiler Q heat − F CHP × 100
Calculator
Enter the values you know and leave one box empty. Calculate finds the empty one, the result or any input.
Worked example
Given
E el E_{\text{el}} E el 160 MMBtu Q heat Q_{\text{heat}} Q heat 240 MMBtu η grid \eta_{\text{grid}} η grid 0.4 ratio η boiler \eta_{\text{boiler}} η boiler 0.8 ratio F CHP F_{\text{CHP}} F CHP 540 MMBtu P E S = 160 0.4 + 240 0.8 − 540 160 0.4 + 240 0.8 × 100 ≈ 22.857 \mathrm{PES} = \frac{\frac{160}{0.4} + \frac{240}{0.8} - 540}{\frac{160}{0.4} + \frac{240}{0.8}} \times 100 \approx 22.857 PES = 0.4 160 + 0.8 240 0.4 160 + 0.8 240 − 540 × 100 ≈ 22.857
Given
E el E_{\text{el}} E el 200 GJ Q heat Q_{\text{heat}} Q heat 320 GJ η grid \eta_{\text{grid}} η grid 0.4 ratio η boiler \eta_{\text{boiler}} η boiler 0.8 ratio F CHP F_{\text{CHP}} F CHP 650 GJ P E S = 200 0.4 + 320 0.8 − 650 200 0.4 + 320 0.8 × 100 ≈ 27.778 \mathrm{PES} = \frac{\frac{200}{0.4} + \frac{320}{0.8} - 650}{\frac{200}{0.4} + \frac{320}{0.8}} \times 100 \approx 27.778 PES = 0.4 200 + 0.8 320 0.4 200 + 0.8 320 − 650 × 100 ≈ 27.778
Symbols and units
Symbol Meaning Unit
P E S \mathrm{PES} PES primary-energy savings % E el E_{\text{el}} E el useful electrical output MMBtu Q heat Q_{\text{heat}} Q heat useful recovered heat MMBtu η grid \eta_{\text{grid}} η grid reference generation efficiency ratio η boiler \eta_{\text{boiler}} η boiler reference heat efficiency ratio F CHP F_{\text{CHP}} F CHP CHP fuel input MMBtu
Symbol Meaning Unit
P E S \mathrm{PES} PES primary-energy savings % E el E_{\text{el}} E el useful electrical output GJ Q heat Q_{\text{heat}} Q heat useful recovered heat GJ η grid \eta_{\text{grid}} η grid reference generation efficiency ratio η boiler \eta_{\text{boiler}} η boiler reference heat efficiency ratio F CHP F_{\text{CHP}} F CHP CHP fuel input GJ
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