Application of exergy-based analysis methods for investigation of a multi-generation energy system: advantages and limitations

Exergy-based analysis methods are often used to analyse energy conversion systems. The main aim of advanced exergy-based analysis namely advanced exergy analysis, advanced exergoeconomic analysis, and advanced exergoenvironmental analysis is to provide the energy system designers and operators with information required to improve the system. Using the advanced exergy analysis, part of the exergy destruction that cannot be avoided due to technology limitation, cost of materials or method of manufacturing could be determined. This method can also be used to determine how big is part of the exergy destruction caused by the inefficiency of the component itself or by the inefficiency of the remaining system components. Traditionally, using advanced exergy analysis, endogenous/exogenous and avoidable/unavoidable exergy destruction are assumed to be negligible in ideal conditions, even for those components where chemical reactions take place. This is not an accurate assumption. Therefore, the aim of this study is to critically evaluate the exergy-based analysis methods and propose how these methods could be improved.

In this study energy and exergy-based analysis methods are introduced and improvements for advanced exergy analysis method are suggested. The improved method with new assumptions is then applied to analyse multigeneration energy conversion system. To perform this study improved advanced exergy, exergoeconomic and exergoenvironmental analysis are conducted and compared with exergy-based analysis methods. The advantages of advanced exergy analysis and limitations of the method, when the methods are being used for analysis of complex energy conversion systems are discussed.

The exergy-based analysis of energy conversion system’s results depend on the choice of reference temperature. To investigate how the costs of the products of ammonia absorption chiller system varies with temperature, exergy analysis is conducted at different conditions. The results of the study show the limitations of exergoeconomic analysis method, especially when it is used for analysis of refrigeration systems.