2.4 Environmental sustainability and Structural materials selection
2.4.4 Evaluation methodology for environmental sustainability – LCA
Life-Cycle Assessment (LCA) is a procedure to assess the sustainability of a product through consideration of all the environmental implications of development, from primary inputs to disposal of final output and by products, including wastes (ISO, 2006). In that respect, LCA has become a widely accepted method for evaluating the environmental impact in not only industrial sectors (Nakayama & Yaguchi, 2002), but also in the construction sector (Aguado et al., 2004; Harris, 1999; Lucuik et al., 2007; Petersen &
Solberg, 2002).
Two possible different approaches to LCA have developed in recent years.
One is to assign elementary flows and potential environmental consequences to a specific product system, typically as an account of the history of the product, which was used in this study. The other one is to study the environmental consequences of possible changes between alternative product systems.
A Life Cycle Assessment is carried out in four distinct phases, according to the ISO 14040 (2006) and ISO 14044 (2006) standards (refer to Figure 2.3).
34 Figure 2.3 Stages of LCA
(Source: ISO 14044, 2006)
Where the goal and scope phase presented problems associated with setting study parameters, the inventory phase presented problems associated with finding and setting modelling parameters.
Inventory involves data collection and modelling of the product system, as well as description and verification of data. This encompasses all data related to environmental and technical quantities for all relevant unit processes within the study boundaries that compose the product system.
A reliable LCA requires the use of reliable Life-Cycle Inventories (LCI).
Three problems occur when using LCI: 1) the allocation problem is one of the most controversial issues of LCA (Rebitzer et al., 2004) and one of the classical methodological problems in LCA (Russel et al., 2005); 2) Inappropriately severe cut-off criteria unnecessarily increase data costs while insufficient criteria leads to the exclusion of consequential flows (Reap et al., 2008); and 3) Local technical uniqueness becomes problematic when average or genetic data or models are used to represent processes that significantly differ from the norm (Reap et al., 2008).
Local data is an important point because in Singapore, reliable LCI data is scarce. In order to apply non-local LCI data in the form most suitable for the Singapore situation, Ossés de Eicker et al. (2009) states that an applicable LCI database should have the following characteristics: 1) all processes must be
Step 1: Life cycle goal and scope definition Step 2: Life cycle inventory analysis
Step 3: Life cycle impact assessment
Step 4: Life cycle interpretation Data collection and
modeling of the product system
Description and verification of data
35
addressed individually; 2) all datasets should be clearly documented; and 3) different alternatives for the same product should be provided, related to technological variations.
2.4.4.2 Application
Several studies have been done to evaluate the environmental soundness of buildings and housing by conducting LCA.
Cole and Kernan (1996) evaluated the life cycle energy of a 50,000 ft2 (4620m2) three-story generic office building for alternative wood, steel and concrete structural systems in Canada. Blanchard and Reppe (1998) studied the total life cycle energy of a standard house in Michigan. They used typical LCA methodology to evaluate the embodied energy of the house. On the other hand, Harmaajậrvi (2000), used the EcoBalance model to study the ecological impacts of eco-villages and he indicated that eco-villages may not be very sound from an ecological point of view. Gerilla et al. (2005) evaluated the embodied emissions of different types of housing construction and materials used. They found out that certain materials in housing construction contribute to an increase in embodied CO2 emissions.
In this study, the LCA-based tools such as BREEAM, LEED and BCA GM are used to develop those criteria under the factor ‗environmental sustainability‘ in the conceptual framework. To obtain LCA data, for example, to investigate the CO2 emission during construction stage, the information that respondents needed to provide were the amount of electricity consumption, diesel consumption, and gasoline consumption.
2.4.4.3 Limitations
The limitations of LCA (Durairaj, 2002) are stated below:
a) The nature of choices and assumptions made in LCA may be subjective.
b) Models used for inventory analysis or environmental impact assessments are limited by their assumptions, and may not be available for all potential consequences or applications.
36
c) Results of LCA studies focused on global and regional issues may not be appropriate for local applications.
d) The accuracy of LCA studies may be limited by the accessibility or availability of relevant data and data quality.
e) Uncertainty in effects of consequences.