An embodied GHG emissions auditing and benchmarking model for assessing the environmental impacts of buildings

Abstract

Climate change constitutes one of the greatest challenges facing the world today, as it will influence the way we live and work in future decades. Excessive greenhouse gas (GHG) emissions are recognized as the key contributor to climate change, and the construction sector has an indispensable role to play in emission reduction, as building facilities are energy- and emission-intensive to construct and operate. Previous research indicates that up to 30 percent of buildings’ lifecycle emissions can be minimized through the careful selection of low-carbon materials. Although building environmental assessment (BEA) tools have been widely used in identifying and mitigating the lifecycle environmental impacts of building facilities, the existing BEA tools provide no rigorous regime for assessing the embodied GHG emissions of building materials. Therefore the aim of this research is to bridge the research and practical gaps by developing an integrated BEA assessment model that comprehensively audits and benchmarks the embodied GHG emissions of building materials at product level.

The research began by examining the limitations of current BEA tools, in particular their means of evaluating the embodied GHG emissions of buildings. Then, an embodied GHG emissions evaluation module model under an existing BEA scheme was proposed. The proposed model comprised (i) product category, (ii) product-based GHG auditing framework, and (iii) emissions benchmarking measure. After that, a thorough review of the relevant literature and international classification systems was carried out to establish a systematic product categorization regime for building materials. An auditing framework comprising system boundary, process map, emission sources, and a carbon auditing tool in Microsoft TM Excel has been developed by reviewing international standards on product carbon footprint assessments and eliciting knowledge from domain experts through a series of interviews. The emission benchmarks for each product category have been determined through the application of fuzzy set theory to facilitate easy comparison and decision-making. Finally, the developed product categorization regime, GHG auditing framework, and benchmarks were validated through a Delphi study, a discussion of which concluded the thesis.

The research outcomes confirm that the GHG emissions embodied in a building facility can be meticulously analyzed and integrated into the BEA. The research also improves the understanding of how the materials’ embodied emissions can be accurately calculated at the product level. More importantly, it enhances existing BEA tools by incorporating embodied GHG emissions into the analysis, thus makes the lifecycle emission assessment of building facilities possible. The proposed integrated BEA model will enable clients and design teams to minimize the carbon footprints of buildings and assist users and the general public in identifying green building facilities. The originality of this research lies in the establishment of a set of emissions benchmarks for five most emission-intensive building materials using fuzzy set theory. These benchmarks provide a seamless platform allowing the assessment of materials’ embodied emissions to be integrated with the existing BEA model, thereby not only encouraging the adoption of low-carbon building materials but also fostering ongoing product carbon footprint reductions.