A Framework for Exergetic Life Cycle Assessment of Residential Buildings

Abstract

This thesis develops a framework for integrating exergy analysis into Life Cycle Assessment (LCA) applied to residential buildings. The central research question addresses whether, from an exergy perspective encompassing both resource use and emissions, it is more sustainable to renovate an existing residential building or to construct a new one using improved materials and low-emission heating systems. The study employs a multi-dimensional exergy-based assessment approach, quantifying three primary categories: (1) Resource Exergy Consumption of Energy (RExC-E), calculated using Resource Exergy Analysis (REA); (2) Cumulative Exergy Consumption including Chemical Exergy Consumption of Materials (CExC-M) derived from standard chemical exergy values and Primary Exergy Consumption of Energy (PExC-E) for construction materials, ;and (3) Chemical Exergy of Emissions (CExE) for environmental outputs. This integrated framework provides a unified thermodynamic basis for evaluating both resource depletion and environmental emissions. The methodology is demonstrated through a case study of a representative 1999 German multi-family row house (Neu-Ulm), comparing three fundamentally different scenarios over a 50-year period (2025–2075): (1) the original building in its existing state; (2) a renovated scenario with thermal envelope improvements and renewable heating; and (3) a new-build scenario with advanced components, timber structure, and efficient systems. Key findings indicate that the renovated scenario yields the lowest Overall Exergy Impact, demonstrating that upgrading heating systems and building envelopes before the end of a building's service life can substantially reduce environmental impacts. The new-build scenario, despite improvements in operational energy, exhibits higher total exergy due to substantial material burdens from new construction. Sensitivity analysis reveals that strategic decisions regarding material reuse, such as retaining the original foundation, can significantly improve the environmental performance of new construction. The study demonstrates that exergy-based LCA can provide robust thermodynamic foundations for sustainability assessment, offering advantages over conventional LCA by incorporating energy quality and enabling unified comparison of resource consumption and emissions. However, limitations remain regarding methodological consistency. The research supports renovation as the most effective strategy for minimizing exergetic and environmental impacts in building stock interventions, while highlighting the critical importance of methodological transparency and scope definition in exergy-based assessments.