Combined heat and power
Making electricity and useful heat (and cooling) from the same fuel.
Recovery and reuse · Heat to power and cogeneration · No. 128
- Recovery and reuse
- Heat grade: All grades
Make electricity and keep the engine's heat, and up to 82% of the fuel does useful work instead of 50-55%.
Chart: Illustration: Combined heat and power
Where it comes from
Chart: Map of where it comes from
A gas engine or turbine makes power, and its hot exhaust and cooling water are captured for steam, hot water or cooling. Packaged units range from 24 kW to 7.5 MW.
Three things to know
- Hot water at 82 C is worth only about 13% of its energy as work, so CHP's real exergy efficiency is about 35-46%.
- An absorption chiller turns waste heat into cooling: double-effect units deliver 1.35-1.42 units of cold per unit of heat.
- Gas CHP emits about 0.21-0.24 t CO2 per MWh after credits, against above 0.64 t for the US marginal grid.
The journey
- 1 FuelNatural gas, biogas or liquid fuel
- 2 Engine or turbineGenerates electricity for the site
- 3 Heat recoveryExhaust and jacket water captured
- 4 Heat or coolingSteam, hot water, or absorption chilling
- 5 Site usersHospitals, factories, campuses and homes