CWA 45547:2004

Manual for Determination of Combined Heat and Power (CHP)

Scope

CHP can make significant fuel and emissions savings over conventional, separate forms of power generation
and heat-only boilers. The generation of electricity from power stations is generally at efficiencies in the range
30-55%, based on the Net Calorific Value (NCV) or Lower Heating Value (LHV) of the fuel. Further losses
occur in the transmission and distribution of electricity to customers. This means that 45-70% of the energy
content of the fuel is not usefully employed. This unutilised energy content is rejected as heat directly to the
atmosphere or into seas or rivers. The generation of electricity and the recovery of heat in CHP plants typically
achieve overall efficiencies of 70-90% and above, corresponding to efficiencies of heat only boilers. The
higher the overall efficiency and the power to heat ratio, the more effective the CHP process.
Unlike conventional methods of electricity generation, in order to achieve such high overall efficiencies, some
of the heat cogenerated in a CHP Scheme is usefully employed in industrial processes or for heating and hot
water in buildings. The heat used in this way displaces heat that would otherwise have to be supplied by
burning additional fuel in boilers or other direct-fired equipment and so also leads directly to a reduction in
CO2-emissions. The development of CHP plays a crucial role in the European energy policy for reducing CO2-
emissions.
The determination of CHP products (heat and power outputs) is important not only for the CHP Directive [1]
but also for the European Emissions Trading Scheme [2], State Aid guidelines for environmental improvement
and the energy taxation Directive [3].