Buildings consume energy throughout their life, not just during their operation phase. A building’s life cycle energy requirement is a total of the energy attributable to the building over its life span (Yohanis & Norton, 2002), including: • initial embodied energy i.e., sum of energy inputs used to manufacture materials and construct of the building (G. P. Hammond & Jones, 2008); • Recurrent embodied energy added periodically to the building though maintenance, renovation, etc. (Dixit, Fernández-Solís, Lavy, & Culp, 2010); • operational energy consumption (which may be measured or modelled); • embodied energy associated with the end-of-life management of the building (Yohanis & Norton, 2002).
57 Emergy being defined usually as solar energy with other energies expressed in equivalent solar
energy, whereas embodied solar calories is based upon the fuel calorific value or equivalent (Brown & Herendeen, 1996).
58 Non-inclusion of environmental support, from solar, geothermal and tidal sources, and human input
Figure 21: Overview of the constituents of a building’s life cycle energy
Figure 21 above shows a slightly modified version of life cycle energy specified for buildings. In the graphic, ET is the sum of energy consumed across the life of the building; EØ is the
operational energy consumption; EE is the embodied energy consumed i.e., that energy that was consumed in the activities required to construct, maintain, renovate and deconstruct the building. Embodied Energy can further be disaggregated59 into following components: • Eα is the energy consumption associated with the project management activities including those involved in delivering the building; • Eμ is the energy consumed in the various processes involved in the manufacture and supply of materials and products for the building; • Eς is the onsite energy consumption by various activities and services that go into constructing and commissioning the building; • Eρ is the energy consumption associated with the materials, goods and activities that go into the periodic refurbishment and renovation of the building and from the waste management activities associated with the wastes generated during refurbishment and renovation;
59 Establishing the boundaries for each component is undertaken as part of the goal and scope
• Eω is the end of life energy i.e., the net energy consumption emissions resulting from the deconstruction, recovery, recycling and disposal activities (including positive flows such as energy recovery) at the end of the building’s (or a part of its useful life.
Figure 21 can also be said to represent a collection of life cycle energy computations for each of the materials represented by Eμ & Eρ components).
Notwithstanding the consumption of energy across the different stages of the building’s lifespan, current approaches to seeking energy savings from buildings, concentrate on so- called operational energy and in so doing, consider only part of the equation. While the historical ratio of operational and embodied energy may have justified such approaches in the past – this is no longer necessarily the case. As buildings become more efficient, using less energy in their operations the embodied energy component automatically accounts for a greater proportion of life cycle energy. Thus, even putting to one side potential increases in the absolute amount of embodied energy of buildings (use to increased processing and additional technologies, etc.)60 It can be seen that its relative significance will increase. An indication of this trend is shown by Sartori and Hestnes’ (2007), review of 60 case studies, in which they found embodied energy accounted for 2-38% of lifecycle energy for conventional buildings, compared to 9-46% for (more) energy efficiency buildings. As buildings’ efficiency increases, so too will the proportion of embodied energy.
However, the historic focus on buildings’ operational phase was justified as it was in keeping with many life cycle energy assessments of conventional office and residential buildings, which showed for typical buildings a large majority of total energy consumption was accounted for by operational energy (Wallhagen, Glaumann, & Malmqvist, 2011). For instance, Yung, Lam & Lu (2013) conducted an “audit of life cycle energy analyses of
60 Additional materials required for insulation and to make buildings more air tight will typically mean
an increase in embodied energy for energy efficient buildings, However, Sartori and Hestnes (2007) interestingly note that (some) passive houses designs, (due to the absence of a conventional heating system) can achieve large reduction to lifecycle energy with only a small increase in (absolute) embodied energy.
buildings” in which they reviewed 206 LCEA case studies found in 36 research works, and
calculated that on average the initial embodied energy expressed as number of years of annual operational energy was 7.8 years for offices and 7.5 years for residential buildings. While for some types of buildings, (e.g., warehouses, high energy efficiency designs), it was accepted that non-operational (i.e., embodied) energy could be of far more significance (Lane, 2007; Sturgis & Roberts, 2010), it was almost a truism, as Ramesh, Prakash, & Shukla (2010) posited, that operational energy was the most important aspect for the design of buildings with lower life cycle energy demand.
However, increases in the energy efficiency of buildings and the additional embodied energy associated with such improvements mean that embodied energy is increasing in significance and it is no longer appropriate that it be disregarded in decision-making. In the context of energy retrofit of buildings, it is obviously important that decision-makers can be confident that the quantity of embodied energy being ‘invested’ in a retrofit is less than the
quantity of operational energy, which will be avoided or ‘saved’ for the expected remaining life of the building. This means that life cycle energy analysis is of growing importance in the construction sector, and that each element of life cycle energy be considered in evaluating the energy implications of renovation61
.
3.4.4 Life cycle greenhouse gases
Introduction
An important driver of public policy initiatives to reduce energy consumption derives from the objective of stabilising atmospheric greenhouse gas levels by limiting their emissions. Another approach to evaluate the success of energy efficiency initiatives is to consider the life cycle effect on such emissions.The so-called carbon footprint is another related concept of LCA, it is a measure of the
61 Certain renovation options could for example result in a greater amount of energy ‘expenditure’ i.e.
embodied energy than would ever be recovered through reduced consumption over the expected life of the renovation
greenhouse gases associated with a product, service, organisation or other defined system. The concept originated in the discourse of ecological foot-printing in the late 1990s. There is a lack of consensus on the exact meaning of the term, but there is broad agreement that it is a quantitative expression of gaseous emissions associated with climate change that are associated with human production or consumption activities. The scope of definitions ranges from measures of direct CO2 emissions only to full life-cycle greenhouse gas
emission inventories, and not even the units of measurement are agreed by all62 (Wiedman
& Minx, 2008; Wright, Kemp, & Williams, 2011).
Figure 22: Spectrum of ‘Carbon Footprint’ definitions
Figure 22 above maps these various definitions and illustrates the range that exists in both the ‘grey’63 and peer-reviewed literature (BP, 2005; Carbon Trust, 2012; Chomkhamsri &
Pelletier, 2011; Energetics, 2007; GFN, 2012; Groppi & Burin, 2007; Hertwich & Peters, 2009; ISO, 2013; JRC-IES EC, 2007; Moss, Lambert, & Rennie, 2008; PCF Pilot Project Germany, 2009; Wiedman & Minx, 2008; Wright et al., 2011).
62 While most quantify ‘carbon footprint’ in terms of mass of emissions, some for example the Global
Footprint Network express the measure as ‘the demand on biocapacity required to sequester (through photosynthesis) the carbon dioxide (CO2) emissions from fossil fuel combustion’ i.e. hectares (GFN,
2012)
In acknowledging such differences, Peters (2010, p. 245) recommends the following open definition: “the ‘carbon footprint’ of a functional unit is the climate impact under a specified
metric that considers all relevant emission sources, sinks, and storage in both consumption and production within the specified spatial and temporal system boundary”. Depending on
the scope selected for, and the approach taken in the preparation of a particular carbon footprint, it will be related to a greater or lesser extent to LCA, with those studies following LCA guidance resulting in a life cycle inventory of greenhouse gases i.e. essentially a subset of an LCA study.
Determining a life cycle GHG inventory64, involves calculating the quantities of individual
greenhouse gases emitted as a result of the various activities attributable to the system under review; these quantities are then converted to carbon dioxide equivalents (CO2e)
using global warming potential factors, e.g., from the Intergovernmental Panel on Climate Change, IPCC (Forster et al., 2007) and a carbon footprint is expressed in terms of mass of CO2e. There are two principal types of such inventory: Product-focussed i.e., “a measure of
the greenhouse gas emissions across the life of a particular product throughout its life cycle” and the organisation-focussed, which “measures the direct and indirect GHG emissions arising from all the activities across an organisation” (Wiedman & Minx, 2008).
As there is no one definition of carbon footprint or GHG inventory it is important that the communication of findings details all underlying assumptions and explains the approach undertaken.
Buildings’ life cycle greenhouse gases
The GHG footprint of a building over its life cycle has been termed life cycle carbon (Kneifel, 2011) or whole life carbon (B. P. Smith, 2008) emissions – in effect such measurements are life cycle inventories of greenhouse gas emissions. This term is used in preference in this document to distinguish between life cycle studies which follow appropriate LCA guidelines64 Assuming it is defined as full life cycle inventory of the ‘Kyoto gases’ i.e. those gases listed in the
and those which may not. As noted previously, reduction of such emissions is increasingly an important complementary objective of building energy retrofit projects. Just as buildings consume energy throughout their life, they are also responsible for GHG emissions. Life cycle inventories of greenhouses gases can be calculated through Life Cycle Assessment based methodologies giving the total GHG emissions generated over the life of a building (including those from non-energy processes) (B. P. Smith, 2008).
Figure 23: Overview of the constituents of a building’s life cycle GHG (M. R. Fay, 1999; Hart & McKinnon,
2010; B. P. Smith, 2008).
As shown in
As shown in Figure 23 life cycle greenhouse gases components have many parallels with those of life cycle energy (and indeed life cycle costs presented on page 88); it has two principal components namely: operational (GHGØ) and embodied greenhouse gases (GHGE)
(Jones 2011), with end-of-life emissions making up a small proportion of the total65. GHG Ø
arises from the consumption of energy and is wholly dependent on the type of energy used. In the past GHGØ accounted for the vast majority of life cycle GHG of typical buildings
(Lane, 2007). GHGE emissions (and potentially credits) arise throughout a building’s life and
may be disaggregated into a number of sub-components (M. R. Fay, 1999; Hart &
65 EOL GHG emissions are categorised by some as part of the embodied GHG emissions (e.g., C. I.
Jones, 2011, p. 5; Sturgis & Roberts, 2010, p. 10), but this is perhaps short-hand for non-operational emissions. Such usage is reflective of the importance of the dynamic between operational and non- operational emissions, and the small proportion of non-operational emissions which arise from EOL activities
McKinnon, 2010; B. P. Smith, 2008), viz., GHG Overhead from project management involved in delivering the building; Materials GHG arising from the manufacture and supply of materials and products; Onsite GHG from onsite construction and commissioning activities; Recurrent GHG from maintenance and renovation of the building; End-of-life GHG from deconstruction, recycling & disposal activities. Thus, building lifecycle GHG emissions can be disaggregated as follows: • Operational GHG emissions – the GHG emitted as a direct result of the energy consumption during the use phase of the building; • Non-operational GHG emissions – those emissions arising from the activities required to construct, maintain, renovate and deconstruct the building; The non-operation GHG emissions may in turn be disaggregated into: • GHG Overhead – emissions associated with the project management activities including those involved in delivering the building; • Materials GHG – emissions arising from various processes involved in the manufacture and supply of materials and products for the building; • Onsite GHG – emissions arising from the various activities and services that go into constructing and commissioning the building; • Recurrent GHG – emissions arising from the materials, goods and activities that go into the maintenance and renovation of the building and from the management choices selected for the wastes generated during these activities; • End-of-life GHG – net emissions resulting from deconstruction, recovery, recycling and disposal activities (including positive/negative flows) at the end of building’s useful life. Operational GHG emissions may be calculated from energy consumption data through the
use of conversion factors for the particular type and source of energy – for example the grid average GHG intensity for the Irish national electricity grid in 2015 was 0.393t CO2 per
MWh (CER, 2016). Non-operational GHG on the other hand does not necessarily have a direct relationship with embodied energy as it also includes process emissions, these are particularly significant in respect of Portland cement (G. P. Hammond & Jones, 2008). The embodied GHG components can be further disaggregated (B. P. Smith, 2008; Sturgis & Roberts, 2010), resulting in an understanding of life cycle GHG emissions as described above. The life cycle greenhouse gas inventory (similar to that for costs and energy as previously discussed) may be expressed as !"!# = !"!∅+ !"!'