A practical, how-to guide covering the main aspects of cogeneration systems that a consultant needs to understand when specifying small-scale CHP.
As the benefits of cogeneration systems - Combined Heat and Power (CHP) - are increasingly recognised and the application of CHP continues to grow, it is essential that consultant engineers involved in the design and specification of building services, and the selection of mechanical and electrical installations, are fully up to speed with the main aspects of this sustainable technology.
For consultant design engineers focusing on continuing professional development (CPD), a CHP skillset is crucial.
What is CHP?
CHP comprises a mechanical prime mover, an electrical generator and a heat recovery system – producing both electrical power and heat energy in a single process.
CHP is installed where its electrical power and heat energy outputs can be utilised effectively, offering higher system efficiencies than conventional energy supplies – national grid electricity and heat from boilers. Instead of wasting process heat, this valuable energy is reclaimed by connecting the CHP’s heat recovery directly to the site’s hot water system.
Why have CHP?
Cogeneration systems provide the end user with:
- Reduced energy costs.
- Improved reliability and security of their energy supplies.
- Enhanced environmental performance.
Compared with conventional means, energy cost savings of up to 40% can be achieved by installing CHP. Reductions in CO2 emissions of up to 30% are possible.
Basic technical and design considerations
To assess whether CHP is suitable for a site:
- Collect accurate energy data for electricity and heating fuel usage.
- Determine the energy profiles.
- Confirm utility connections are available.
- Select the CHP size that best matches the energy demands.
- Check that the CHP unit and its ancillary equipment will physically fit.
- Assess environmental performance gains.
- Large-scale: large industrial applications.
- Small-scale: small industrial sites and buildings.
- Micro-scale: domestic and small commercial properties.
CHP has been successfully used in:
- Manufacturing and production facilities.
- Leisure centres and hotels.
- Supermarkets, warehouses and distribution centres.
- Hospitals, universities, schools and prisons.
- Local community heating schemes, residential centres and large offices.
Basic product types
There are basically two types of CHP:
- Packaged: for small-scale applications.
- Custom-built: bespoke designs (mainly large-scale applications).
CHP units are available in various output sizes – used for both:
- Cogeneration systems (CHP).
- Trigeneration systems (CCHP - Combined Cooling Heat and Power). The heat energy also can be used to produce cooling.
CHP units are fuelled by natural gas, biogas, biofuel or diesel.
Calculating CHP benefits
In order to maximise the benefits of CHP, it is essential that Good Quality CHP is selected and installed.
One of the main indicators of CHP benefit is the calculation of the spark spread. This is the difference between the purchase price of the CHP fuel and the sell price of the electrical power output. CHP applications ideally require a spark spread of around 3 or more.
Incorrectly sizing a CHP unit will result in potential benefits being missed.
- Keep up to date with CHP technology and legislation for your CPD.
- A CHP skillset allows you to offer clients significant benefits and energy savings.