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The thermoeconomics combines economics and thermodynamics to provide information not available from conventional energy and economic analysis. For thermoeconomics modeling one of the keys points is the thermodynamic model that should be adopted. Different thermodynamic models can be used in the modeling of a gas turbine system depending on the accuracy required. A detailed study of the performance of gas turbine would take into account many features. These would include the combustion process, the change of composition of working fluid during combustion, the effects of irreversibilities associated with friction and with pressure and temperature gradients and heat transfer between the gases and walls. Owing to these and others complexities, the accurate modeling of gas turbine normally involves computer simulation. To conduct elementary thermodynamic analyses, considerable simplifications are required. Thus, there are simplified models that lead to different results in thermoeconomics. At this point, three questions arise: How different can the results be? Are these simplifications reasonable? Is it worth using such a complex model? In order to answer these questions, this paper compares three thermodynamic models in a gas turbine cogeneration system from thermoeconomic point of view: cold air-standard model, CGAM model and complete combustion with excess air.

Cost allocation, optimization, and diagnosis are the main application fields of thermoeconomics. Cost allocation allows evaluating the plant cost formation process. For plants containing dissipative equipment, the use of total exergy flows in the conventional productive diagrams is not able to isolate these components. The physical exergy disaggregation, despite increases the complexity, allows the treatment of dissipative equipment and residues. Nevertheless, conventional productive diagrams based on productive flows and fictitious units to connect the subsystems, may not take into account the physical connections existing in the system flowsheet, making the cost formation process arbitrary. The comprehensive diagram uses both flow types, physical and productive, and the subsystems are interconnected according to the physical flows of the flowsheet. This work aims to demonstrate that the combination of exergy disaggregation and comprehensive diagram avoids arbitrariness. The application of the localized exergy disaggregation at the comprehensive diagram reduces the complexity. A gas turbine cogeneration system is chosen as one application example. Productive and comprehensive diagrams are compared with total and localized disaggregation and a systematic procedure to treat waste and dissipative equipment is presented. The reduction of complexity is performed by means of localized disaggregation and the arbitrariness related to the productive diagram is evaluated.

Thermoeconomics connects thermodynamic and economic concepts in order to provide information not available in conventional energy and economic analysis. Most thermoeconomicists agree that exergy is the most appropriate thermodynamic magnitude to associate with cost. In some applications, exergy disaggregation is required. Despite the improvement in result accuracy, the modeling complexity increases. In recent years, different exergy disaggregation approaches have been proposed, mostly to deal with dissipative components and residues, despite all of them also increasing the complexity of thermoeconomics. This study aims to present a new thermoeconomic approach based on exergy disaggregation, which is able to isolate dissipative components with less modeling complexity. This approach, called the A&F Model, splits the physical exergy into two terms, namely, Helmholtz energy and flow work. These terms were evaluated from a thermoeconomic point of view, through a cost allocation in an ideal Carnot cycle, and they were also applied and compared with the UFS Model, through a cost allocation analysis, in a case study with an organic Rankine cycle-powered vapor compression refrigeration system. The complexity and computational effort reduction in the A&F are significantly less than in the UFS Model. This alternative approach yields consistent results.

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