The role of thermodynamics in life cycle assessment of existing and emerging technologies

Some of the outstanding challenges faced by traditional LCA include the following. LCA is mainly an "output side" method due to its focus on emissions and their impact, but such data are often difficult to find, particularly for emerging technologies. Furthermore, although an important goal of LCA is to evaluate the environmental sustainability of technological alternatives, the very ecosystem goods and services that sustain all economic activities are usually ignored. This paper describes how thermodynamics can complement and enhance LCA by addressing these challenges. Ecosystem goods and services may be represented as the cumulative exergy consumed in ecological processes necessary for producing them. This may be calculated via methods in systems ecology and combined with engineering thermodynamics for joint analysis of industrial and ecological systems. A thermodynamic input-output model of the US economy is developed based on this approach, and is used for hybrid LCA. Accounting for ecosystem goods and services is likely to provide a reasonable proxy to life cycle impact even without knowing details about emissions and their impact. This is because as per the second law, exergy is not conserved, but is lost in each transformation step. The exergy lost to the surroundings creates disorder in the environment, which should be related to the impact of emissions. This implies that among alternatives with similar utility, the process with a higher life cycle thermodynamic efficiency should have a smaller life cycle environmental impact. This talk will present some examples as preliminary support of this hypothesis and describe challenges and on-going work for obtaining a more rigorous statistical validation.