In the race to net zero, operational carbon remains crucial Despite all the recent claims, it’s not all about embodied carbon

22 November 2023 by Jason Quinn

Lloyd Alter is a Canadian adjunct professor and writer on sustainability topics. Like a growing number of commentators, Lloyd is brushing off the impact of operational carbon and arguing for the need to radically focus on lowering embodied carbon: building with low carbon building materials and methods that are low or zero carbon and retrofitting and renovating existing buildings rather than tearing them down to rebuild. In fact, he has a whole book forthcoming that advances this argument.

Modelling I’ve personally done shows that operational carbon is not inconsequential or even secondary to embodied carbon. I think this topic is one of those cases where the way you ask the question is more important than the answer. Embodied carbon calculations are only useful insofar as they guide good decision making. His essay shows some graphs Lloyd used in a presentation but I can’t see the calculations behind them. When it comes to calculating something like this, how we phrase the question is very important. Results can be meaningless unless it is clear what is counted—and what isn’t. Lloyd writes, ”As our buildings become more efficient and we decarbonize the electricity supply, emissions from upfront carbon will increasingly dominate and approach 100% of emissions.” I don’t believe this is correct.

Buildings emit more carbon over their lifespan from operational carbon (which includes plug loads, not just energy for heating and cooling) than the carbon emitted to construct them. That’s still true even when powered by a fully renewable grid, which lowers the carbon cost of operational energy requirements. There is no such thing as a zero carbon grid: it has to be built and maintained and all of that emits carbon. We can have a net zero carbon society (including our environment) but generating power is never going to be free of carbon emissions unless you weirdly exclude stuff that actually counts.

I’ve run the numbers myself for very optimised dwellings—all timber, of Passive House quality— using New Zealand’s relatively clean electricity grid and still the operational carbon outweighs the embodied carbon. If you build a reasonable building, the operational carbon emissions over a quite short lifetime of 50 years still outweigh the embodied carbon. That remains true if you take into account a fully renewable energy grid as is predicted in New Zealand. I’ve written previously about the impact of using short lifetimes to analyse these numbers and how it distorts the outcomes.

The only way I was able to flip the primacy of embodied vs operational carbon was on the basis of a horrible building constructed from concrete and insulation with high global warming potential. (I did note the buildings illustrating Lloyd’s post were mostly concrete.)

The colleague who forwarded me this post liked Lloyd’s argument that ‘embodied carbon’ was a poor description that is better labelled ‘upfront carbon’. Whatever the name, it’s referencing the carbon released into the atmosphere by constructing a new building, including the carbon cost of the materials, transport etc.

I’m not a fan of a new label. Upfront carbon obscures the reality that a building’s embodied carbon footprint continually increases as it is maintained or renovated. For example, in a coastal location, a steel roof needs to be replaced every 20-30 years due to corrosion. This maintenance cycle needs to be tracked in the embodied carbon calculation. The result may prompt a different choice at design stage, perhaps choosing a material that has higher embodied carbon but which is more durable, thus delaying maintenance or replacement costs. Embodied carbon calculations need to track that too.

I’m OK with using upfront carbon to refer to those emissions from LCA stages A1 to A5. But focusing on this portion of embodied energy over-simplifies things in my opinion. It’s possible that the upfront emissions number can be overtaken by the carbon emitted by maintenance and replacement.

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