ENVIRONMENTAL PERFORMANCE ASSESMENT OF CHP SYSTEMS WITH AVOIDED HEAT GENERATOR APPROACH

This paper is focused on methods to indicate the environmental impact in terms of air pollutants of CHP (Combined Heat and Power) systems. The aim is to combine the energy saving achievement with information concerning the environmental benefit, in comparison with the non-CHP scenario. Environmental impact of CHP production both on global and local scale should be taken into account. In particular, the method of the “avoided heat generator” is highlighted in this study as a proper approach for CHP and is used for a local-scale environmental impact evaluation. This approach calculates the reduction of emission due to CHP operation, taking into account the amount of pollutant emitted by an equivalent heat generator, which provides the same thermal power of the CHP prime mover. Moreover, the recommended approach is compared in the paper with another proposed method, based on the PSI (Pollutant Saving Index) value, which is suitable to estimate the global-scale environmental impact. Numerical evaluations of the CHP environmental benefits, in terms of NOx, CO and CO2 emissions, are shown for various CHP systems with different technologies and electric power sizes. The significant effect of the reference comparative scenario is highlighted.