A new approach to exergoeconomic analysis and design of variable demand energy systems

Exergoeconomics is an attractive research field regarding the optimisation of design and operability where complex energy systems are concerned. The different approaches to thermoeconomics can easily achieve optimal or near-optimal solutions for the design of energy systems in industrial applications, characterised by regular energy demand profiles; for applications in buildings, however, the great number of components operating at unsteady conditions due to the demand variability make these methodologies hard to use. Furthermore, in project phases of complex plants such as Combined Heat and Power (CHP) or Combined Heat Cooling and Power (CHCP), energy demand can be satisfied with different output shares among the various components. In this paper, a simplified exergo-economic methodology is presented, which is based on aggregate consumption data and on a case-oriented procedure for analysis simplification. A technique to internalise exergy flows between the considered energy system and other external systems is also introduced. The proposed approach was applied to a trigeneration plant serving a 300-bed hospital situated in a Mediterranean area; the obtained results were finally compared with the optimal solution previously determined by means of demand cumulative curves and plant running simulations.