Optimization of trigeneration systems by Mathematical Programming: influence of plant scheme and boundary conditions

The large potential for energy saving by cogeneration and trigeneration in the building sector is scarcely exploited due to a number of obstacles in making the investment attractive. The analyst often encounters difficulties in identifying optimal design and operation strategies, since a number of factors, either endogenous (i.e. related with the energy load profiles) and exogenous (i.e. related with external conditions like energy prices and support mechanisms), influence the economic viability. In this paper a decision tool is presented, that simultaneously optimizes the plant lay-out, the sizes of the main components and their operation strategy. For a specific building in the hotel sector, a preliminary analysis is performed to identify the most promising plant configuration, in terms of type of cogeneration unit (either microturbine or diesel oil/natural gas-fuelled reciprocate engine) and of absorption chiller. Then, some sensitivity analyses are carried out to investigate the effects induced by: a) tax exemption for the fuel consumed in “efficient cogeneration” mode, b) dynamic behaviour of the prime mover and consequent capability to rapidly adjust its load level to follow the energy loads.