Modern society is underpinned by a complex web of economic and social activities; commerce, transport, and leisure interweave providing support to not only sustain, but also enhance our way of life. In doing so we have created unprecedented environmental impacts and a burden that must be carried by our planet and our planet alone. Much of this burden is associated with cities, which appear to 'sustain' immense populations and satisfy the consumption activities of its many inhabitants. Unfortunately such activities normally require a quantity of natural resources well beyond the bio-capacity of its locality. For example, the 'Georgian' city of Bath, in the UK, has been estimated to have an environmental footprint 20 times larger than that of the neighboring land in the area (Doughty and Hammond, 2004). In modern times such trends in over-consumption are not uncommon. Urban immigration is expected to continue, and it is estimated that by the year 2025 three-quarters of the world's population will be living in a city (Rogers, 1997). This places greater burden on existing city infrastructure and potentially hinders progress toward true sustainability. It is therefore clear that widespread change is required, and without which we will quickly deplete the carrying capacity of our planet. It has already been estimated that we are currently exceeding the carry capacity of our planet by 20% (Loh, 2002). Clearly concerted action must be taken not only to limit but also to reverse potential long-term damage, and thus ensuring that we live on this planet in a sustainable manner.
Sustainable development can be defined as "Meeting the needs of the present without compromising the ability of future generations to meet their own needs" (Brundtland, 1987). Such aspirations require broad sweeping actions in order to ensure economic and social development, while securing environmental protection, across each sector of the economy. Each sector has its own part to
I. Dincer et al. (eds.), Global Warming, Green Energy and Technology,
DOI 10.1007/978-1-4419-1017-2_23, © Springer Science+Business Media, LLC 2010
play, and the building sector is a large energy-consuming and carbon-releasing sector, that is responsible for almost half of the UK's total energy consumption and carbon emissions (Brown et al., 2006). However, the additional embodied impact of construction must be considered. The construction industry requires the extraction of vast quantities of materials, resulting in the consumption of energy resources and the release of deleterious pollutant emissions to the biosphere. Each material has to be extracted from the Earth, then processed, and finally transported to its place of use. The energy consumed during these activities is therefore critically important for human development, but they also put at risk the quality and longer-term viability of the biosphere as a result of unwanted or 'second'-order effects. Many of these side effects of energy production and consumption give rise to resource uncertainties and potential environmental hazards on a local, regional, or national scale (Hammond, 2000). Energy and pollutant emissions, such as carbon dioxide (CO2), may be regarded as being 'embodied' or associated with materials. Here embodied energy is viewed as the quantity of energy required to process and supply to the construction site the material under consideration. In order to determine the magnitude of this embodied energy, an accounting methodology is required that sums the total of the energy consumed over the major part of the material supply chain or life cycle. In the present context, this is taken to include raw material extraction, processing, and transportation to the construction site: a 'cradle-to-site' approach. Likewise the emission of energy-related pollutants, like CO2 that is a concern in the context of global warming and climate change, may be viewed over their life cycle. This gives rise to the notion of embodied carbon. Embodied impacts are often forgotten and apparently concealed from view. With estimates of 7.6 to 10.8 million new dwellings to be constructed in the UK by the year 2050 (Palmer et al., 2006), the embodied or 'concealed' impact of such residential construction must be considered.
Energy analysis may be used to estimate the embodied energy of a product. Several differing methods of energy analysis have been developed (Boustead and Hancock, 1979; Champan, 1976; Hammond and Jones, 2008a; Slesser, 1978), the most significant being statistical analysis, input-output (I-O) analysis, process analysis, and hybrid analysis. The latter method bridges elements of I-O and process analyses in an attempt to remove some of the downfalls of each individual method (see for example Treloar et., al., 2000). The analysis of a product over its life cycle is a complex and involved activity. It requires the consideration of a large number of processes, and as such gaps often appear in the data. Studies often have different boundary conditions or cut-off points. In 1974 the International Federation of Institutes for Advanced Study (IFIAS) described the concept of 'level of regression' for analysis (IFIAS, 1974), which is a structured method of pruning a data tree. Figure. 23.1 displays this concept, indicating the relative contribution (in many cases) of each level to the total life cycle energy (the area of the triangle).
A first level of analysis includes only the direct energy consumption. It is normally expected that the results of a first-level regression will represent the majority of the life cycle energy. This does not, however, imply that a first-level analysis is sufficient on its own, as this is rarely the case. A second level of regression additionally considers energy that was required to manufacture feedstock materials (material production energy). It has been estimated that in many cases a second order of analysis can account for 90% of the total life cycle energy (Slesser, 1978). This is, however, merely a guideline, and deviation from this 'rule' does occur. While this may hold true for many building materials there will be many systems and activities that fall outside of this 'rule of thumb.' Analysis beyond this level is time consuming and hence studies of this order and above are rare. A third level of regression includes energy consumed while manufacturing capital equipment (energy required to manufacture machines). And finally the machines from the third level of analysis were themselves manufactured from other machines. As such a fourth level of regression exists.
In the case of steel production a first level of regression would include the energy consumed in direct production processes. This includes energy consumed directly in the blast furnace and fabrication processes. The second level of analysis would include energy that was consumed during the quarrying and mining of feedstock materials, such as the iron ore consumed during the steelmaking process. A third level of regression would include energy that was required to manufacture the blast furnace (capital equipment). And a fourth level would consider the energy that was required to manufacture the machines that manufactured the blast furnace. The contribution from a fourth level of analysis is usually minor and very time consuming to determine. However, if a fourth level of analysis was never undertaken its 'insignificance' could never be concluded with absolute
Fig. 23.1 Pyramid of representation.
Fig. 23.1 Pyramid of representation.
certainty. As such in the first investigation of a system it is desirable to complete an energy analysis to the highest attainable level of regression that is possible.
Energy analysis preceded environmental life cycle assessment (LCA) and it shares much of the same fundamental methodology (Hammond and Jones, 2008a). It is widely recognized that in order to evaluate the environmental consequences of a product or activity the impact resulting from each stage of its life cycle must be considered. This has led to the development of ecotoxicology, a study of the harmful effects of releasing chemicals into the environment, and a range of analytical techniques that now come under the 'umbrella' of environmental LCA. In a full LCA, the energy and materials used and pollutants or wastes released into the environment as a consequence of a product or activity are quantified over the whole life cycle, 'from cradle-to-grave.' The aim of the LCA is often to identify opportunities for environmental improvement by detecting the areas with the most significant impacts. In the case of non-energy-consuming products, for example, buildings materials, the energy result of an environmental life cycle assessment can often be taken to be its 'embodied energy.' The latter is often confined within the boundaries of cradle to site to separate it from the operational energy. However, end-of-life impacts are inevitable and as such are often integrated into the boundaries of embodied energy studies. An LCA should ideally conform to international standards (ISO 14040, 2006a; ISO 14044, 2006b).
Determination of a product's life cycle is invariably difficult; it requires the elementary understanding of material, energy, and emission flows across a broad spectrum. It is complicated by the fact that many such contributions are apparently hidden or 'concealed' from view. For example, if a consumer were to estimate the full impact of its activities they would need to consider a significant number of 'concealed' activities. It may be considered that many consumers live in a 'virtual world' in which they interact directly. This bears the bulk of their considerations. But what lies outside this world is an unavoidable and essential web of ancillary activities. The consumer is rarely exposed to such activities and as such they have little awareness of the resulting impacts. The marriage of the two worlds leads to the real, 'actual world,' as represented by Fig. 23.2. In the case of driving a car, as illustrated in Fig. 23.2, a consumer believes that he/she achieve 50 miles to the gallon (mpg) fuel economy (5.65 liters per 100 km). However, this does not bear the full environmental impact. There is an entire web of ancillary activities that must be considered, which includes each process leading up to the delivery of fuel into their vehicle in a usable format and at a convenient location. Progression up the production tree would reveal such activities as fuel pumping, delivery, refining, shipping, storage, oil well operations, drilling, and exploration activities. Once the impact of such activities is accounted for the actual (or 'true') fuel economy may be only 45 mpg (6.28 liters per 100 km). In reality the consumer may have only a modest direct influence on such ancillary activities. But were they to start considering them from a consequential point of view, then they might exhibit wider environmental concern than just taking into account
the burden of their virtual world (i.e., their own interactions). Thus, they may become impelled to think about not only conserving energy, but conserving all that they undertake and consume.
23.2.3 The Inventory of Carbon and Energy (ICE)
In order to enable the determination of embodied energy and embodied carbon of buildings a robust, reliable, and transparent database is required. Initial research proved that finding such a database in the public domain would be difficult, this was especially true for embodied carbon (embodied carbon coefficients naturally carry a higher uncertainty than embodied energy as a result of variations in fuel mixes, electricity generation technologies, and process technologies). For these reasons the present authors at the University of Bath decided to develop their own database for a wide range of materials. This resulted in the creation of 'The Inventory of Carbon and Energy' (ICE) (Hammond and Jones, 2008a and 2008b). This inventory contains the embodied energy and carbon of approximately 200 materials and has been released freely into the public domain. The ideal data would involve undertaking complete environmental LCA for each individual material, but with a likely material inventory amounting into the hundreds, and each LCA requiring up to 9 months to undertake, this was not considered feasible. For such reasons the data were sourced from the literature and may be considered to be a summary of the current knowledge base.
During the creation of ICE it was quickly discovered that estimating the embodied carbon from literature sources would present difficulties, even more so than any difficulties experienced for embodied energy. In the first instance it was determined that only 20% of the collected data was usable for estimating embodied carbon. The ideal resource was to obtain embodied carbon from a full-scale environmental LCA. But these were not normally available. For the majority of materials the embodied carbon was therefore estimated through calculation. When considering a material list in the region of 200 materials it is vital that an efficient and reliable method be applied in the conversion of embodied energy to embodied carbon. A generic emissions factor would be the quickest way to achieve this, and such methods are available in practice. However, there are a number of reasons for avoiding such methods. Application of a generic emissions factor (i.e., the average UK emissions per unit energy consumed) may offer acceptable results for a large number of materials. There are many cases when errors are induced. Possible causes of such errors include:
■ A generic emissions factor neglects to consider that certain industries have fuel mixes that differ significantly from the average. As an example, worldwide aluminum production is known to utilize a high percentage of hydro-electricity. The net effect of this is to reduce the embodied carbon below that based on national emissions factors. Despite this the absolute embodied carbon of aluminum per kilogram remains high.
■ Generic factors do not account for non-fuel-related emissions of individual materials (process emissions). Such emissions play an important role for several key building materials. In the manufacture of cement, for example, carbon dioxide is released into the atmosphere as a result of material processing. In this case it contributes in the region of 60% to the total embodied carbon; the remaining 40% is attributable to fuel-related carbon dioxide (Hammond and Jones, 2008a and 2008b). Cement is the largest process-related carbon dioxide emitter. Other materials that experience non-fuel-related emissions are glass and ceramics, the latter including clay and bricks.
Further errors may be induced as a result of the following:
■ Embodied energy is a measure of primary energy and as such it is vital that the correct emissions factors are applied. Emissions factors for delivered electricity differ by an approximate factor of 3 with those converted into its primary energy equivalent.
■ It is important to understand what the data include. Many of the traditional energy analysis studies are calculated via the gross calorific value (also known as the higher heating value). Environmental LCA results are often (although certainly not exclusively) calculated by net calorific value (also known as the lower heating value). In the case of embodied energy this could result in a 5-11% difference, although this should in theory have no effect on the embodied carbon results unless errors subject to the above misinterpretations have been induced. For example if carbon emissions factors for gross calorific values were applied to embodied energy calculated by its net calorific value.
There is additionally the complication of organic materials, materials such as timber which absorbs carbon dioxide during the growth phase of trees. Whether to include or exclude this factor is not a simple matter. The authors of this chapter prefer to exclude the sequestered carbon dioxide from their data until such a time that timber demonstrates to be operating in a globally sustainable manner (see Amato, 1996; Eaton and Amato, 1998; Hammond and Jones, 2008a). At present this is not the case, and consequently global tree populations are in decline.
After consideration of the above matters, a methodology for converting embodied energy to embodied carbon was developed. The method has proven to be effective and reliable. It represents a large improvement over industry-wide (generic) emissions factors and is displayed in Fig. 23.3 below.
Once the embodied energy has been determined the process of converting to embodied carbon begins. In the absence of LCA results containing embodied carbon the present method was applied (see Fig. 23.3). First it was necessary to estimate the embodied energy breakdown by fuel type. To achieve this, the fuel mix used in the most relevant industrial sector was applied. Appropriate emissions factors were then applied to obtain the fuel-related carbon dioxide emissions. Once the additional carbon dioxide release has been determined the total embodied carbon had been estimated from the sum of these and fuel-based emissions.
The system boundaries for this study were adopted as appropriate for 'cradle-to-site' studies. Feedstock energy was included only if it represented a permanent loss of valuable resources, such as fossil fuel use. Thus, fossil fuels utilized as feedstock for the petro-chemicals used in the production of plastics were included (although identified separately). However, the calorific value of timber has been excluded. This approach is consistent with a number of published studies and methodologies, including the BRE methodology for environmental profiles (Howard et al., 1999). The effects of carbon sequestration (for example, in the case of timber) were considered, but not integrated into the data. Non-fuel-related carbon emissions have been accounted for (process-related emissions) and a recycled content, or cut-off approach, was preferred for the handling of recycling (i.e., metals).
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