Costructal law, exergy analysis and life cycle energy sustainability assessment: an expanded framework applied to a boiler

Life cycle sustainability assessment (LCSA) is one of the most relevant tools delving in sustainability science, based currently on the triple bottom line idea that is defined as the contemporary implementation of the three tools of life cycle assessment (LCA), life cycle costing (LCC) and social life cycle assessment (S-LCA). The methodology is currently being applied to a wide set of products and systems. However, as per in the large interest towards energy-related products, the sustainability assessment of energy systems—in particular those where fluid streams are used—could be more effective if some further stages could be included in the analysis, i.e. a process level analysis with regard to energy quality and exergy, and a more thorough energy analysis of the fluid flows available to achieve an optimal design of the system.

This paper proposes an extended framework for LCSA introducing two additional stages to the methodology: Constructal law (CL) inspired analysis of the energy design of the system and exergy analysis (EA) of the system and its life cycle. A fully developed case study (a biomass boiler) is proposed, described the extended life cycle energy and sustainability assessment (LCESA: LCA, LCC, S-LCA, CL, EA), highlighting both the quantitative results related to each section together with the strengths and limits of the methodology, while stressing the potential applications as, e.g., decision support tool and support to the design of energy system.

The results highlight different and optimized designs for the boiler through a constructal law–based analysis and several hot-spots throughout different stages of the life cycle, ranging from the production stage of steel for most environmental indicators in LCA to the cooking stage for the exergy analysis. Relevant positive impacts are traced also in the S-LCA point of view during both the use and production step.

The methodology could represent a potential advancement towards the LCSA application to energy technologies as it highlights some limits and proposes specific advancements.