Bases Teóricos o Científicas

The concept of embodied energy and CO2 emissions analysis, albeit with significant variations in methodological approach, is used to estimate the energy and the resulting CO2

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emissions from materials used in the construction industry (Acquaye, 2010). As shown in the foregoing analysis, it is clear that the inclusion of embodied energy in lifecycle building energy assessment is important. For years, the concept of embodied energy has been an integral part of the debate towards a sustainable future, but despite all the advantages of its inclusion in lifecycle emission analysis of buildings, there is currently little incentive to integrate the calculation of embodied emissions in construction decision making (Hamilton-MacLaren et al., 2009). The reasons are partly due to challenges associated with methodological framework, the focus of regulations on operational energy and carbon, the lack of appropriate legislation and a lack of interest in the impacts of embodied energy by the public and industry stakeholders (Hamilton-MacLaren et al., 2009; Rawlinson and Weight, 2007).

Additionally, the long period of time and the demanding data collection procedures that are required for the quantification of embodied emissions make it difficult. This is particularly so because the tracking of raw material from their original sources requires data that are reliable based on the manufacturing processes and supply chains (Engin and Frances, 2010). Due to the time-consuming requirement and the variation in accuracy of embodied energy calculation results, their adoption in the decision-making process when conducting building energy assessment and performance analysis has to a very large extent been restricted.

2.8.1. Data quality

The complexity and uncertainty associated with the estimation of embodied energy and the associated CO2 emissions is made worse by problems with data collection, variations in technology manufacturing processes, as well as the number, diversity and interactions of processing steps (Acquaye, 2010). Additionally, there is a lack of reliable information about embodied energy in products, and this affects both embodied emissions calculations and the decisions based on them (Fernandez, 2006; Pears, 1996).

Variations in calculation results of embodied emissions hinder the process of selecting environmentally friendly materials (Pears, 1996; Davies, 2001). Such comparisons may be invalid if they are based on data with different energy values (Atkinson, 1996; Pullen, 1996). Pacca and Horvath (2002) also noted that uncertainties in embodied energy analysis can also come into play through problems such as economic boundary and methodological constraints, which also affect decision making. Published results of embodied emissions are inconsistent and in many cases the results are not comparable due to differences in calculation procedures, age of data and a host of other factors as detailed in Dixit et al., (2010). Results also vary between countries due to the specific energy mix and transformation processes as well as manufacturing technologies (ibid).

35 2.8.2. Complexity of analysis

Another major challenge in embodied carbon emissions calculations is that many variables (e.g. primary energy sources, manufacturing process, lifespan of products, chemical processes, transport fuel type and the extent of waste or recycling) affect the carbon intensity of products (Engin and Frances, 2010). However, the carbon intensity of some products, for example aluminium, cement and glass, are considerably higher than others, so it might not be absolutely essential to compute the total carbon footprint associated with a project, due to the fact that most individual components will have impacts that are negligible and provide limited opportunities for emission mitigation purposes (Rawlinson and Weight, 2007).

For the case of a building, computation of its embodied emissions based on lifecycle assessment framework is not straightforward as highlighted by Dixit et al, (2012); Ramesh et al.

(2010); Khasreen et al. (2009); Nebel and Gifford (2007). This is particularly so, as buildings are highly varied in size, form, and function. They are complex and have a unique nature. Hence, their design and construction often involves bringing together a wide range of manufactured materials and products. Tracking material flows, products and all the processes involved in the construction of a building with a view to evaluating its total lifecycle emission is non-trivial due to non-uniformity of the systems boundary of buildings.

When compared to other products, the life spans of buildings are much greater. As such, substantial effort, in terms collection of data, analysis and interpretation is required in order to track and assess lifecycle emissions. Given that buildings undergo changes including alteration, extension, retrofit and refurbishment, due to their dynamic nature, and are characterised with maintenance and replacements activities, the process of data collection for lifecycle emissions assessment is made even more difficult (Ramesh et al., 2010; Nebel and Gifford, 2007). Unlike other manufactured products, the standardisation of processes involved in the construction of building is limited, making the collection of data a difficult task (Dixit et al., 2012).

Behavioural influences and the complex interplay, in terms of different motivations of key stakeholders, involved in a building’s delivery process also further compound the problem (Ramesh et al., 2010; Nebel and Gifford, 2007). The lack of up-to-date data regarding energy and environmental impacts of building materials and components makes the calibration of buildings difficult with respect to their embodied energy content, within a lifecycle assessment framework (Ramesh et al., 2010).

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Due to these challenges which stem from diverse and inconsistent datasets as well as complexity of analysis, there is no method available to estimate embodied emissions with the required level of accuracy and consistency that is currently accepted generally (Acquaye, 2010), although a general framework exists in the ISO 14000 series of standards. As a result, wide discrepancies in embodied emissions measurement results are unavoidable, because of various other factors responsible for inconsistency and disparity in embodied energy results which are well detailed in Dixit et al. (2010) and Hamilton-MacLaren et al. (2009). However, in the pursuit of near zero-carbon buildings, the inclusion of embodied emissions is becoming increasingly important, as operational emissions associated with buildings fall in response to new regulations.

The UK Carbon Plan (HM Government, 2011) has provided new definitions of useful benchmarks in the traded/non-traded price of carbon¹. These benchmarks reflect the global cost of the damage caused by a tonne of carbon over its lifetime, and have been used to appraise proposals and policy initiatives. Additionally the UK Government has recently established a mandatory carbon reporting scheme for companies. These new schemes indicate that embodied emissions are likely to become one of the standard metrics to be addressed in lifecycle emissions assessment of buildings. Its inclusion in the decision-making process is therefore necessary.