Thermo-mechanical energy level approach integrated with exergoeconomic optimization for realistic cost evaluation of a novel micro-CCHP system

Abstract

Conventional exergoeconomic analysis suffers from a lack of solid conceptual meaning behind its auxiliary cost equations defined for the needed components. To provide a logical relation between auxiliary cost equations, here a modified exergoeconomic analysis is used, which integrates the energy level of each stream with the conventional exergoeconomic analysis. Since the energy level of a component stems from a temperature (known as thermal term) and pressure (known as mechanical term) difference between its inlet and outlet streams, modifying the unit cost of the streams by their energy level significantly affects the overall unit cost of product. Hence, in this study, a new integral micro-CCHP (combined cooling, heating, and power) system driven by geothermal source and working with different zeotropic mixtures is proposed and evaluated economically by employing the recommended modified exergoeconomic approach. Later, due to the existing conflicting trend between energy efficiency, exergy efficiency, and modified total unit cost associated with the products, a multi-objective optimization tool is used to merge several optimal design points into an equilibrium point as the final optimal point. Several similar benchmarks (in terms of applications or sketch) are selected and the superiorities of the devised micro-CCHP system over them in terms of thermodynamics and thermoeconomics have been demonstrated. After optimization, the net power, cooling load, and heating load are improved by 106.77%, 142.83%, and 49.78%, respectively. This improvement in all products has led to a meaningful enhancement of 24.91% in energy efficiency, 15.42% in exergy efficiency, and 9% in the total unit cost of product (TUCP) (in both modified and conventional cost approaches). The best representative optimal point has the optimal energy efficiency, exergy efficiency, and TUCP of 61.61%, 44.46%, and 0.63 $/kWh, respectively.