Capital goods in life cycle inventory of products: a global systematic review and future research agenda

Abstract Purpose The absence of capital goods data in several life cycle assessment (LCA) studies has stimulated the need to understand the role of capital goods in life cycle inventories (LCI). Capital goods may include manufacturing machinery, factory halls, power plants, transmission lines, roads and sewage systems. Undoubtedly, capital goods represent a crucial part of LCI datasets, although their data points are heterogeneous in LCA settings. The predominant rationale expressed for the exclusion of capital goods in LCA product systems relates to the complex and inexact data requirements and the possible ambiguities and inconsistencies in existing LCA standards and guidelines. This study seeks to identify critical research gaps whilst mapping recent LCA publications that have incorporated and/or discussed capital goods in their studies. Methods In order to identify the research gaps and map contemporary knowledge surrounding the role of capital goods in LCAs, this study conducted a systematic literature review following the PRISMA approach. Altogether, a hundred papers were compiled from proprietary databases and reviewed using bibliometric techniques. From these, 25 case studies documenting capital goods in terms of scope, explicit archetypes and LCI data sources and reporting any recommendations for practice were critically reviewed based on a rigorous content analyses approach. Results and discussions Overall, the review evidence that 84% of the selected studies utilize process based LCA. Equipment and building being the dominant inclusion amongst the capital goods archetype, with energy infrastructure receiving least attention. Capital goods contribute up to a median value of 1 – 18% of the GWP across different sectors. However, the contributions of capital goods across other LCIA indicators vary considerably, with highest median impact in ADP non-fossil (90%) and SQP (82%). Capital goods inclusion in LCAs require more empirical data to better understand and holistically appraise the environmental performance of products. As a practical contribution, a roadmap for future research on capital goods research is proposed. Furthermore, the adoption of advanced estimation techniques underpinned by digitalisation holds immense potential in achieving improved accessibility and availability of capital goods data. Conclusion Data uncertainty and complexity remain major concerns regarding capital goods inclusion in LCAs. This study suggests the optimal approach to accessing reliable capital goods data entails a multifaceted process: a process encouraging rigorous primary data collection through implementing advanced technologies and uncertainty analyses techniques alongside continuous existing database upgradation to minimise uncertainty and enhance reliability and comprehensiveness of LCA outcomes.