Q3a: Operational vs. Embodied Energy

How do operational impacts compare to embodied impacts on the carbon footprint of a building? 

Authors: Frances Yang, Rebecca Jones ; Contributors: Megan Stringer, Matthew Comber

The approximate average across several case studies (Perez, 2008; Ramesh, 2010; Junilla, 2006) is 20% of the total life-cycle energy, as often cited in the building practice.  However, as recorded in Figure 1, the results amongst these studies actually ranged from 5% to near 30%. 

Figure 3a-1: Ranges of typical embodied and operational energy proportions found in literature

This range resulted from differences in what was included or excluded, the building life assumed, and the operational performance.  Figure 2 shows the typical trend of both embodied and operational energy over a typical 60 year building life.  It illustrates that arriving at a 20/80 proportion of embodied to operational is very sensitive to building life.  (For more info on what structural engineers can do to account for building life in LCA, see Q4 and Q9.)

Figure 3a-2: Typical breakdown of embodied and operational impacts over 60 year building life

The studies referenced in Figure 1 concluded that operational performance was most dictated by climate and occupant behavior.  The resulting proportions of operational to embodied included intentional reductions in operational impacts from low-energy designs. (Perez, 2008; Ramesh, 2010; Junilla, 2006)  The fourth cited study of Figure 1 performed a particularly rigorous analysis to test this proportion. Basbagill ran a conceptual building design through all possible permutations of preset values within 31 variables that defined shape, massing, materials, systems, and dimensions. Figure 3 shows a random sampling of 5000 of these scenarios, from which a mean ratio of embodied to total life-cycle impacts of 18.66% is extracted (Basbagill, 2013).

Figure 3a-3: Embodied Impact as % Total, the remainder being the energy to operate the buildings. (Credit: Basbagill et al, used with permission)

The significance of Basbagill’s study is that it reveals even larger scatter that departs from the often cited 20/80 ratio. It illustrates that design decisions can affect the operational and embodied outcomes significantly, such that a singular focus on the operational portion may be too narrow a view.  At the same time, the average of the permutations in Basbagill’s study reinforces the expectation that most designs will land near the 20/80 split.

If operational impacts can be expected to be of such great significance, structural engineers should be aware of opportunities for structural materials (the embodied impacts) to participate beneficially to reduce operational impacts.  Therefore, perhaps a more meaningful question to ask is “What active and passive technologies in low operational energy buildings require special structural solutions?”

References

Basbagill, J., Lepech, M. (2013). “Characterizing Life Cycle Impacts of Conceptual Building Designs”. Energy and Buildings (in preparation)

Junilla, S., Horvath, A., Guggemos, A. (2006). “Life-Cycle Assessment of Office Buildings in Europe and the United States,” Journal of Infrastructure Systems.  ASCE Press. March, p. 10-17.

Perez Fernandez, Nicolas, (2008). “The influence of construction materials on life-cycle energy use and carbon dioxide emissions of medium size commercial buildings,” School of Architecture, Victoria University of Wellington, July.

Ramesh, T., Prakasha, R., Shuklab, K. K. (2010) “Life cycle energy analysis of buildings: An overview,” Energy and Buildings, 42, p.1592–1600

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