A framework for the integrated optimisation of the life cycle greenhouse gas emissions and cost of buildings
Introduction
There is growing concern about the effect that buildings are having on the environment [1], [2] with construction being one of the most energy intensive sectors and contributors to greenhouse gas emissions (GHG), in developed countries [3]. Over the years there has been an increase in efforts to understand the energy and GHG associated with the built environment. This increasing awareness has led to the creation of several forms of building evaluation that aim to analyse a buildings’ environmental performance and suggest ways to reduce energy demand and GHG [4], [5], [6]. However, the focus has largely been on reducing the operational energy and GHG of buildings, leaving the embodied energy and GHG largely ignored [7] despite their demonstrated significance. For example, embodied GHG have been estimated to equate to between 10 to 97% of the total life cycle GHG associated with a building (depending on the building location, type, material use, assessment methods and assumptions) [8]. Thus, the need to consider a building's performance from a life cycle perspective has become increasingly evident. However, building design that considers the life cycle perspective has been slow to take hold due to a number of barriers [9]. These include lack of a commonly accepted assessment method, lack of reliable data, and lack of mandatory legislation [10], [11]. Another barrier is the uncertainty towards the financial cost of life cycle environmental optimisation. Building decision-makers are unsure of the full cost implications of this optimisation and building design professionals often don't have sufficient knowledge or appropriate tools to address these concerns. Limited consideration of costs from a life cycle perspective is also a key barrier to life cycle optimisation, as financial decisions are mainly based on the initial cost of building design options, often not taking into account future maintenance and operational costs [12]. The cost-effectiveness of solutions for reducing a building's GHG has become a critical issue for building owners and one of the main drivers behind their uptake [13]. It has become vital to provide environmental and financial building analyses not only from an early-design stage, to better inform design decisions [14], but also to integrate the results in order to better understand their respective trade-offs. Several studies have aimed to integrate these two forms of assessment, typically using life cycle assessment (LCA) (either from an energy or GHG perspective) and life cycle costing (LCC), and include those such as Petrillo, et al. [15] and Savino, et al. [16]. However, several barriers still plague their successful integration. This study aims to address these barriers and proposes an improved integrated life cycle GHG and LCC framework to aid early-stage building design decision-making.
The aim of this study was to develop and test a framework that integrates life cycle GHG and LCC assessment of buildings to aid early-stage building design decision-making. For this study, the environmental impact category of Global Warming Potential (GWP) has been used, which measures how much heat a GHG traps in the atmosphere and is expressed in carbon dioxide equivalent (CO2e). The greenhouse gases considered include carbon dioxide, methane and nitrous oxide. The scope for the life cycle GHG assessment includes the initial and recurrent embodied GHG and operational GHG. The LCC system boundary includes the initial, replacement and operational costs. The end of life stages, such as demolition, disposal and recycling have not been considered in this analysis due to the limited amount of data available for these life cycle stages (Moncaster and Song, 2012) and as they have been shown to represent less than 1% of the life cycle GHG associated with a building [17], [18]. The scope of the study is illustrated in Fig. 1.
This paper is structured into five sections. The next section, Section 2, provides a brief overview of some of the previous studies that have aimed to integrate life cycle GHG and LCC analysis. This section concludes with the identification of the gaps and weaknesses of these previous studies and highlights how this study attempts to address them. Section 3 describes the process involved in developing the integrated life cycle GHG and LCC framework. The framework is then applied to a residential building case study in Section 4 in order to demonstrate and test its potential. This is followed by the discussion and conclusion in Section 5.
Section snippets
Previous studies attempting to integrate life cycle greenhouse gas emissions (or energy) and life cycle cost analysis
Environmental and financial assessment of buildings has been largely carried out in isolation of each other, but there has recently been increasing attempts to combine them. In most cases LCA is used to carry out the environmental assessment either from an energy and/or GHG perspective. For the financial analysis, LCC is predominantly used. Previous studies, such as Fouche and Crawford [19], have provided a detailed review of the previous attempts at integrating LCA and LCC. These can be
Developing an integrated life cycle greenhouse gas emissions and life cycle cost framework
In order to develop an integrated framework a series of steps had to take place. The first step, of identifying the gaps and weaknesses of previous studies, has been detailed in Section 2. The next step was to identify and select appropriate life cycle GHG and LCC quantification techniques (Section 3.1), followed by identifying the key parameters associated with these techniques and the approach for visualising the integrated results (Section 3.2). Next, a brief description of the integrated
Case study
The aim of this section is to demonstrate the potential of the integrated framework by applying it to a detached residential building case study located in Melbourne, Australia. A detached building has been selected as it represents over 80% of Australia's residential building stock [66]. Fig. 3 provides a plan of the 230 m2 4-bedroom building. The external brick veneer walls (with timber studs and internal plasterboard finish) have a U-Value of 0.35 W/m2 K, and roof (timber truss and concrete
Discussion and conclusion
Studies such as that by Bierer, et al. [27] confirm that there is an undisputed need to couple LCA and LCC in order to increase their uptake within the construction industry. This study sets about addressing this need and has provided a framework that integrates LCA (in the simplified form of a life cycle GHG analysis) and LCC. It is the first integrated approach, in the form of a framework, that aims to address some of the most critical gaps and weaknesses associated with previous attempts at
Acknowledgements
This research is funded by the CRC for Low Carbon Living Ltd supported by the Cooperative Research Centres program, an Australian Government initiative, under the Integrated Carbon Metrics Project (RP2007).
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