The aim of the paper is to present an energy system optimization method, based on the Fuel Impact Formula, able to overcome typical limitations of previous formulations. In particular, the methodology allows time dependent production levels to be considered and on-off operation and presence-absence of any component to be modelled by means of binary decision variables and inequality constraints. These often happen if the synthesis and operation of Combined Heat and Power (CHP) systems are considered at the same time. Moreover, the effect of replacing actual not linear thermodynamic inputs-output relations of each component with linear, or even proportional ones, is highlighted in the paper. Finally, an example of application is shown, dealing with a multi-component DH and CHP system in the tertiary sector.
