How Simplified Building System Data Distorts LCAs: Insights from a Swiss Case Study

Abstract Heating and ventilation systems account for circa 30% of embodied environmental impacts in residential buildings. Yet, current life cycle assessments (LCA) often rely on oversimplified datasets, particularly in early design stages, due to missing or generic data for technical building systems. This study addresses the limitations of aggregated datasets and emphasizes the need for more detailed, component-level inventories. Using a case study of a new multi-family building in Zurich, we compared environmental impacts derived from standard Swiss database values (KBOB) with those based on in-depth inventories built from manufacturer data, environmental product declarations (EPDs), and ecoinvent datasets. The analysis covered life cycle stages A1-A3, B4 and C1-C4 over a 60-year period, following SIA guideline 2040 and EN 15978 standards. The detailed approach revealed that simplified LCAs overestimate embodied emissions by 17% and embodied energy by 12%. As a result, projects may appear non-compliant with climate targets or miss cost-efficient reduction opportunities. While rooted in the Swiss context, the findings highlight the broader relevance of improving HVAC system data quality in early-phase assessments. The study also proposes guidelines to streamline future LCAs without sacrificing accuracy, helping bridge the gap between design-phase feasibility and environmental performance.