Exergy-based ecological indicators: From Thermo-Economics to cumulative exergy consumption to Thermo-Ecological Cost and Extended Exergy Accounting

This paper presents a summary of the conceptual development and the practical applications of exergy-based Environmental Indicators. After a brief historical introduction, the two most popular methods are presented and discussed: the Exergo-Environmental Analysis (here TEA, as a memento of Jan Szargut's original denomination "Thermo-Ecological Analysis", currently adopted also by Valero's school) and the Extended Exergy Accounting (EEA). Both emerged from Szargut's idea of the existence of a consumption index, the Cumulative Exergy Consumption (CExC), which can be used to quantify the consumption of primary resources "embodied" in a final product or service. The extension introduced by both methods with respect to CExC consists in the explicit inclusion in the exergy budget of one or more of the Externalities, lumped in the original CExC formulation into the exergetic material contents of the single commodities. The differences between the three formulations are obviously reflected in the numerical values of the resulting indicators. The Thermo-Ecological Cost (TEC) and the CExC differ because of the inclusion in the former of the exergetic resources that reflect the "penalty" in the use of primary non-renewable consumption caused by the anthropic intervention. The CExC index and the Extended Exergy Cost EEC differ because the latter explicitly includes in the calculation a "Labour and Capital equivalent exergy consumption" that allows for the survival of the individuals in a given region according to the respective life standards (variable in space and time). Another difference is the way the Environmental Externality is computed: while TEA takes an ex-post assessment, EEA introduces a calculation of the -ideal or real-remediation costs.