Great question. We are generally talking about the greenhouse gas (GHG) emissions in carbon dioxide equivalent (CO2e) terms related to the post construction phase of a building’s life up until its demolition. The main ones people immediately think about are the CO2e emissions from burning on-site fossil fuels and the upstream emissions from electricity usage. There are also emissions from water consumption and wastewater production. And if refrigerants are used which have a global warming potential (GWP) greater than zero, then any leakage from those refrigerants results in fugitive emissions considered to be operational carbon.
Let’s do a quick primer on terminology as this is a jargon heavy discipline.
The GHG Protocol establishes 3 distinct categories for GHG emissions. For simplicity I’ll define them thusly:
- Scope 1 emissions related to a building are those from on-site combustion of fossil fuels and fugitive emissions from refrigerant leaks.
- Scope 2 emissions are those upstream emissions related to electricity use provided by the utility grid.
- Scope 3 emissions are virtually everything else like cars of visitors (not company owned), water and wastewater, materials, etc. [The building’s Scope 3 emissions are someone else’s Scope 1 and 2 emissions.]
From this point we also layer on EN 15978-2011’s Whole Life Carbon for its nomenclature.
- Module A (A1-A5) will cover the materials and construction phase of the building.
- Module B (B1-B7) includes maintenance and operations during the building’s life.
- Module C (C1-C4) covers the building’s end-of-life emissions from demolition and disposal.
Operational Carbon is therefore in the B module. And there’s a clear crossover into the C module.
Let’s simplify things into these modules of interest:
- B1 will include the refrigerant leakage during building operations which will by the earlier definition be a Scope 1 emission.
- B6 will include all operational emissions from fossil fuel uses on-site, which are Scope 1 emissions and also includes electricity consumption which are Scope 2 emissions.
- B7 will be the energy-water nexus and is the embedded carbon in water conveyance and treatment to bring the water to the building and the wastewater exported from the site to a treatment facility. These are Scope 3 emissions.
- C1 is included by some as an operational carbon albeit per 15978 it’s listed as an end-of-life Scope 1 emission. But consider that the end of service life for an AC unit or chiller will occur many times during the course of a normal building’s life.
Here’s a handy diagram from our friends at NBI to show these:
Hopefully this is clear but if not please ask questions or make corrections!