This study quantifies the gap between net-zero energy and net-zero carbon through a life cycle assessment (LCA) of a net-zero energy building (NZEB) in Ahmedabad, Gujarat, India. The annual net-zero energy evaluations of a building do not account for the greenhouse gas (GHG) emissions released before the building operation phases. Nor does it account for the GHG emissions during the end-of-life processes. As a consequence, an NZEB may not be a net-zero emission building over its lifespan. Comprehensive carbon-based evaluations are necessary to ensure an overall reduction in emissions is in line with the goals of the United Nations Paris Agreement. The LCA frameworks of ISO 14040 and EN 15978 form the basis of analysis and a method is presented based on data collection, consistency checks, uncertainty evaluation, impact assessment and interpretation of the results. It also acknowledges the lack of a nationalised inventory for LCA in India. The results show that despite an annual net-zero operation status of a building, the building has a negative impact with 866 tCO2e across a calculated lifespan of 60 years. The case study reveals the sensitivities of the analysis towards the system boundary, data quality requirements and acceptable limits of uncertainty.

Practice relevance

For an NZEB in Ahmedabad, the life cycle GHG emissions were calculated to be 866 tCO₂e. Although the building has a net-zero energy status for its operational phase, it does not have a net-zero carbon status across its lifespan when embodied and end-of-life processes are considered. This comprehensive approach enables the possibility to compensate for these emissions. For example, the NZEB can target a net-zero carbon status within a planned time frame through the provision of additional electricity generation using solar photovoltaic panels. The quantification of carbon requires a context-specific, regional and temporal life cycle inventory. The inventory developed for this case study can be used for many buildings in Gujarat built between 2012 and 2018. Expanding the research can lead to possibilities of benchmarking and standardisation. The methodology can also be adapted for existing buildings across India.

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