• trigeneration
• energy saving

Trigeneration refers to systems that are able to produce, simultaneously, different types of energy utilities, as electricity and heating and cooling power, by means of various technologies. Combined with district heating and cooling (DHC) network, they can reduce the amount of primary energy required to achieve the same kind of services with standard systems. The different technologies involved in a trigeneration power plant are closely interconnected and their optimal management can be highly complex both from an economic and energy-saving point of view. Furthermore, particularly in the first stages of implementation of the project, the power required by the various users can be significantly lower than the installed power. This raises a number of issues connected especially to the impossibility to avoid a low partial load of the trigeneration plant. For these reasons, the use of computer software can be extremely useful in solving the problem. Real monitored data taken from the polygeneration Cerdanyola del Vallès plant, placed into the POLYCITY project of the CONCERTO initiative, have been used to model, with linear relationship and binary variables, characteristic units of such a type of system. Typical trends of the cooling demand and of the import/export electricity price have been used as input to the MILP model. In particular, the energy demand of the selected days must be representative enough to reproduce the same results that would have been obtained considering a complete period, as a month or a season. The optimization environment selected for the resolution is GAMS. The model has been initially used to derive the operational schedule that allows maximizing the gain of the trigeneration plant and the results have been compared with the real strategy. Nevertheless, economic optimization turns out not to be sufficient for guaranteeing the best primary energy savings, particularly during partial load. Therefore, an in-depth investigation has been conducted to identify the best sharing load between the thermal chillers and a sensitivity analysis to find the necessary parameters to work, conveniently, in cogeneration.