Hybrid Life Cycle Assessment of Greenhouse Gas Emissions in Australian Built Environment across Scales

Abstract

As the built environment is being the main contributor to global greenhouse gas (GHG) emissions, a growing number of studies are conducted to assess the life cycle GHG emissions of individual buildings. However, the precinct-scale assessment incorporating infrastructure and occupants’ activities is often limited. This study applied a newly developed hybridised Australian life cycle inventory (LCI) database to assess the life cycle GHG emissions of Australian built environment across scales starting from building products, via buildings to a precinct. This coherent bottom-up assessment framework ensured the consistency of system boundaries as well as the completeness, transparency, and comparability of data. The precinct-scale life cycle GHG emissions were comprised of embodied emissions, operational emissions and transport emissions, which took up 18%, 48% and 34% of the life cycle emissions, respectively. Major emissions hotspots of each category were identified, and accordingly, twelve commonly applied emission reduction measures, including the deployment of solar photovoltaic, the use of electric cars and energy efficient appliances, the replacement of carbon-intensive construction materials and the change of occupants’ behaviours, were suggested and quantified. With mature technologies status in quo and minimal system disruption, the scenarios demonstrated an achievable emissions reduction potential of 26%, and the most effective measures were related to operational and transport emissions. Meanwhile, the results from hybrid life cycle assessment (LCA) were compared with the results obtained by conventional process-based LCA to demonstrate the comprehensiveness of hybrid LCA method and to elaborate how the results were influenced by applying different LCA approaches. This comparison concluded the use of hybrid LCA not only resulted in higher GHG emissions for each category, but the distribution of emissions among them was also altered. This could potentially change the prioritised emission reduction areas and the most significant impacts were seen on embodied emissions. On average, the embodied emissions from the hybrid analysis was 26% higher than the corresponding process-based analysis. This ratio was reduced to 6% and 16%, respectively, for operational and transport emissions. The significance of this study is multi-faceted. For LCA researchers and practitioners, this study expands the accessibility of hybrid LCA by developing and applying a pre-compiled hybrid LCI database; for city planners, developers and architects, it implies the impact of precinct morphology and renewable energy on precincts' GHG emissions; for construction managers and building product manufacturers, the selection of building materials is relevant; and for occupants, the suggestions on behaviour change become valuable.