The Relationship Between Operational Carbon and Fuel Sources
Understanding these coefficients is crucial for assessing the climate impact attributable to the various fuel sources utilized in a building
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Image courtesy of author.
It is well documented that the building sector is a significant contributor to global carbon dioxide (CO2) emissions. By some estimates, our buildings are responsible for up to 42 percent of total global CO2 emissions. These emissions stem from two primary sources:
- Building operations (up to 27 percent of global emissions)
- Embodied carbon (up to 15 percent of global emissions)
Regarding operational carbon emissions, the amount of CO2 released into the atmosphere will correlate with the fuel sources utilized by a given building. Many buildings utilize a combination of electricity along with fossil fuels for on-site combustion—and both resources are typically provided by one or multiple local utility companies, who provide services to the building site through an infrastructure that the companies own and operate.
In certain circumstances, a building may utilize on-site energy resources in lieu of, or in concert with, the energy resource(s) delivered by the utility service.
By definition, decarbonization requires electrification
Pursuant to decarbonization efforts, an increasing number of buildings are being designed to only use electricity because doing so lends to the potential for utilizing 100 percent renewable energy source—which, in theory, would result in virtually zero operational carbon emissions (in reality, though, we are far from this a decarbonized electrical grid).
Logically, full decarbonization of operational energy requires some combination of on-site renewable energy resources and an electrical utility grid that utilizes zero emission fuel sources (e.g., renewables and/or nuclear energy). This notion is reflected in the White House's National Definition of a Zero Emissions Building.
Why understanding and documenting fuel sources matter.
Different fuel sources result in different magnitudes of carbon dioxide emissions. In fact, the U.S. Environmental Protection Agency (EPA) maintains carbon dioxide (CO2) emission coefficients to help articulate this. These emission coefficients represent the amount of CO2 released per unit of fuel consumed. They indicate the amount of carbon dioxide released per unit of energy produced. Under the International System of Units (SI), the coefficient indicate the kilograms of carbon dioxide emissions released per million British thermal units (kg CO2/mmBtu) generated. The coefficients vary significantly depending on the fuel type. For example:
- Energy from coal has high emissions, typically averaging over 95 kg CO/mmBtu.
- At just over 53 kg CO2/mmBtu, emissions from natural gas are roughly half that of coal.
- Generating electricity from renewables (e.g., wind or solar) and nuclear energy result in near-zero emissions.
Figure: Carbon dioxide emissions coefficients by fuel source. Information source: U.S. Environmental Protection Agency. Figure by Daniel Overbey.
Understanding these coefficients is crucial for assessing the climate impact attributable to the various fuel sources utilized in a building. Considering the vast majority of projects use some degree of carbon-emitting energy, a project's energy conservation measures (ECMs) remain a primary means by which a design team may reduce operational carbon emissions. However, just as important is a clear understanding of the fuel sources being utilized by the project along with developing a decarbonization plan (which is required in LEED v5 BD+C) to effectively eliminate operational carbon emissions as soon as possible.
