Combined heat and power has traditionally been associated with industrial sites. However, advances in the technology are opening it up to a wider market. Chris Sears reports.
While estates and facilities managers across local authority sites such as large school campuses are under increasing pressure to reduce their carbon footprint, they are equally keen to cut their energy bills.


CHP plants are viable for any site where there is a heavy demand for power alongside heat in the form of hot water. Where cooling is also a need then tri-generation plants can be employed.

The education environment brings its own considerations such as how to heat classrooms; provide ample heating or cooling for larger areas like assembly halls and reception spaces; respond to the demand for additional energy in science or home economics labs; where there are residential facilities for students how will these be catered for so there is always hot water when it is needed; where there are sports facilities onsite, where the energy and heat for these will come from and what the energy manager would do in the event of a power failure; all at what cost?

Local energy network

CHP generates power onsite so large schools and education campuses on a university scale can make savings and benefit from an onsite energy source. Fuel, usually natural gas but more frequently now renewable biogas, biomass, and biodiesel, is burnt to produce energy, which is transported around a local energy network.

The by-product - heat, usually in the form of steam - is not rejected as in traditional energy generation but instead it is also captured by the CHP plant's exhaust gas heat exchanger and directly connected, via a plate exchanger, to the site's own heating system.

A feasibility study is the first action. At this stage an engineer will survey the education site to establish its energy requirements, outlining the initial costs alongside the ensuing financial benefits and payback period. Those with expertise in sizing CHPs according to a site's current and projected needs will use purpose-designed software to establish the parameters; from the overall size of the building or buildings to be supplied with heat and electricity, to the site's base load - the electrical and thermal load experienced during non-peak periods. From this data it is possible to optimally size the CHP engine required.

Because of the rising application of CHP outside its traditional remit in the industrial sector there are now ranging sizes of plant available and output can range from around 30kW to 3MW. At the largest end of this scale a 3MW CHP engine might typically be needed to supply the energy needs of a large university campus.

The results are a site that operates its energy use far more efficiently, when compared to utilising grid-fed energy.

An efficient CHP plant will not only enable a site to greatly reduce its reliance on electricity imported from the National Grid, but will also mean energy is much more efficiently utilised. Many large education sites, for instance, will be able to reduce their overall carbon footprint by more than 25 per cent.

A typical CHP plant will have a thermal output of around 1.5 times its electrical power output.

A 1,000 kWe (or one megawatt) unit, fuelled by standard natural gas will show an annual saving of some 5,000 tonnes of CO₂ over conventional electricity generation and heat supplied from gas-fired boilers.

Developments in the technology also mean that alternative fuels can be burnt, enabling further enhancement of the carbon savings available.

For example, biomass in the form of waste wood provides a renewable form of fuel that generates clean energy and helps to reduce the carbon emissions still further.

Reduced electricity importation

Although the precise level of savings a school or university campus can achieve will be determined by a number of factors, an efficient CHP system with electrical output accurately configured to match the base load will typically reduce a site's importation of electricity from the National Grid. The significant reduction in the volume of electricity a site needs to import, coupled with far more efficient operation of heating and hot water systems can equate to an annual energy bill reduction of anything up to 50 per cent providing a short term payback period followed by annual savings.

So with a drastic reduction in carbon emissions there is a clear environmental case for schools and those in the education sector to think about CHP.

The cost savings speak for themselves too but many educational campuses, particularly where costs are being drastically cut, are put off by the initial investment required. Now, however, there are routes to funding that require no capital outlay.

Schemes such as Eco2Synergy run by Dalkia enable customers to have a CHP unit installed and operating on their site, with a fixed monthly fee and no surprises covering the fuel they burn and that which they generate at a reduced rate.

The resulting cost means heat captured as part of the process is an added bonus. The overall concept provides a risk-free route to onsite energy generation for smaller education sites.