Efficiencies and indicators defined to promote combined heat and power

Efficiencies and other indicators of the performance of combined heat and power (CHP) are reviewed and compared. The emphasis is put on those indicators that are used in the legislation of Belgium (Flanders, Brussels and Walloon regions), the Netherlands, Spain, Portugal, the UK and the USA. These are compared with an exergy based evaluation of CHP. Several series of test cases are run for a boiler and steam turbine (ST) plant and with a gas turbine (GT) plant with heat recovery steam generator (HRSG) and steam turbine. Both plants are simulated with two different steam pressure levels, and varying steam delivery loads by either reducing firing or increasing the condensing tail steam turbine (CTST) loads. All indicators used in the legislations are based on energy. It was seen that only the US, Dutch and Belgian indicators credit the better utilization of a GT system compared to a ST system. All indicators discourage high load on the CTST, and most of them are stronger than if based on the exergy efficiency. Contrary to the evaluation by exergy efficiency, low pressure steam is favored to medium pressure steam by all the indicators.