Exergy-Based Lumped Simulation of Complex Systems: An Interactive Analysis Tool

The paper describes an application of a computational tool developed for the extended exergy accounting (EEA) of complex systems. The application is presented in an interactive graphic form to enhance its impact on the user. The computational part is based on a modular process simulator, originally devised to compute the mass- and energy balances and the exergy accounting of energy conversion systems: the modularity of the code suggested its extension to the analysis of complex energy systems. The main characteristics of the package are its extensive modularity and its ability to handle a wide spectrum of system configurations. The code identifies a system by means of an interconnection matrix, which represents the structural connectivity of the society under examination (i.e. which describes in a synthetic way the interactions of each mass- or energy flux with each sector of that society), and assembles the system of balance equations according to an original protocol. In steady-state simulations, as the one presented here, the code is capable of assembling the proper balance equations starting from the information about an ‘initial state’ of the system, specified by the user together with all necessary constraints. The extension to unsteady operation is not foreseen at the moment. The level of aggregation, the relevant input data and boundary conditions must be assigned by the user, and are scrutinised by the code for internal consistence. Except for this preliminary check, and for the mass- and energy balances at ‘run’ time, the procedure is entirely acritical about the input data, thus allowing a very broad range of sensitivity studies. The total amount of the resources entering the control volume must be assigned, either directly in exergetic form, or otherwise by means of mass- and specific energy flow rate values: the code executes a simple screening on the input data and computes the exergetic value of the incoming flows with the help of a table of ‘raw exergy data’ available in one of its libraries. Energy- and exergy balances are performed independently: the package generates energy-, exergy- and extended exergy ‘balances’. Irreversible losses are computed separately for each component of the system. The advantage of EEA consists in the inclusion in the system balance of the exergetic equivalent of human work (labour), of capital and of environmental remediation costs. As an application, a series of simulations have been performed on the ‘System Italy’ (on a 1996 database).