Models and toolkit to estimate and analyse the emissions and environmental impacts of building construction

摘要

Levels of emissions to the environment imposed by human activities have been growing at an alarming rate over the past few decades. Buildings contribute a significant proportion of this total impact because of their consumptions of significant material and energy over the lifecycle. Studies have indicated that the building sector consumes about 40% of the materials entering the global economy and emits approximately about 33% of the environmental emissions. To solve the problem, life cycle assessment (LCA) as a powerful tool can be used to analyse their environmental effects for a building it includes production and transportation of building the materials phase, the construction phase, the operation/ maintenance phase and the end-of-life phase. However, very few studies have been found concentrating on the construction phase of the building. Most of the previous studies either ignore or approximate the effects of the construction phase when comparing to the total life cycle environmental impacts of the building. Several reasons can be found for this, such as data collection and inventory issues, lack of reliable software and site specific complications. Following the introduction of carbon tax, (currently not active) the contractors and designers in Australia are more interested in reducing the emissions at the construction stage. A simple method is lacking which enable users to compare and evaluate emissions at various activities at the construction stage. Hence, in this study, a process based emission analysis was proposed to critically evaluate the environmental emissions from the construction stage of a building. Several models and methodologies were also developed to carryout in-depth emissions analysis in view of critically investigating the emission patterns in the foundation & structure construction stages. These emissions were then converted into environmental impacts to compare its significance to the global, regional and local environment. Three case studies have been considered for the analysis: two typical high-rise residential and one commercial building construction. On-site data collection was conducted to obtain the major input data required for the emission analysis. Apart from on-site data, energy reports, bill of quantities (BOQ), project timelines and daily progress reports were used to collect data. The results were then utilized for developing a simple toolkit that would enable to compare and estimate emissions at construction stage with minimum effort. Emission results obtained at the foundation construction stage indicated higher proportion of greenhouse gas (GHG) emissions from equipment and transportation compared to that in the total building construction. Considerable amounts of non-GHG emissions such as Nitrous Oxides (NOx) and Carbon Monoxides (CO) were also recorded at foundation construction level. Impact assessment for foundation construction at the three levels resulted that other impacts apart from global warming carry significance at local level. However, indirect emissions such as embodied GHG emissions from materials have an overwhelming contribution at the structure construction stage of a building. The project level emission analyses acknowledged the necessity of an in-depth analysis to identify emission reduction opportunities. Scenario analyses on different emission sources and techniques implied that resource planning and construction technique selection is critical in minimising emissions subjected to satisfying site related constraints. The outcomes of this research enable designers and contractors to compare and estimate the emissions at the construction stage of buildings and thereby to optimise the decision making on effective execution of the construction workflow. These outcomes are presented through developed models and methodologies and ultimately in terms of a user friendly toolkit with inbuilt databases. These enhanced decision making processes enable stakeholders to effectively estimate, analyse and compare emissions at different construction stages of buildings.