Rethinking exergy efficiency in favor of exergy sustainability as a criteria for design

Engineering design in power generation or conversion has typically focused on minimizing exergy losses (entropy gains), or maximizing economic returns. Both entropy minimization and profit maximization are readily obtainable and acceptable objective criteria for design of thermodynamic processes. However, sustainability concerns are not addressed by efficient or economy alone. Previous research presented a framework for considering minimal environmental impact as an alternative design criterion for minimizing the pollution potential of exergetic wastes. This paper proposes a mathematical model for maximizing resource renewability. A life-cycle metric describing the replacement time frame of the primary exergy source is presented. When coupled, the two metrics together partially assess the overall sustainability of the design.