Carbon: Operational vs. Embodied

Article originally published in the June 2020 issue of the FES Journal

It’s no secret that carbon plays a critical role in our environment. The balance of carbon between its sequestered (or stored) state and its atmospheric state determines the health and well-being of our planet. Carbon storage occurs primarily in food chains (plants and animals), the ocean and fossil fuels and cycles between these locations and the atmosphere. When this exchange is in balance, the storage locations have the capacity to manage the carbon levels in the atmosphere. However, when this balance is disrupted, excess carbon combines with oxygen in the atmosphere to become CO₂ and traps heat at our Earth’s surface, causing global warming.

The built environment assumes its fair share of blame in the greater global warming discussion, but this blame typically encompasses operational carbon — the carbon released into the atmosphere as a result of the building’s energy consumption. Functionally, operational carbon’s impact occurs at the utility’s energy plant as fossil fuels are processed to generate the energy needed at the building. Particularly over the last 20 years, building codes and organizations like ASHRAE and LEED® have devoted significant time and research to reducing our built environment’s operational carbon impact. More often than not, design teams are now required to demonstrate whole-building energy efficiency through energy modeling. This energy efficiency is accomplished through strategies such as efficient lighting sources, comprehensive building automation controls, efficient mechanical systems, renewable energy and envelope characteristics and varying the shape, size and orientation of the building on the site. On the existing building side, municipalities are incorporating energy benchmarking ordinances that require owners to meet stringent energy use intensities.

While operational carbon is important, it is not the whole picture and maybe not even the majority of the picture. Embodied carbon is the environmental impact associated with extracting, manufacturing and transporting building materials to the job site. Unlike operational carbon, which can be continually reduced through energy efficiency measures, embodied carbon is locked in time when the building is complete. A building’s embodied carbon budget has already been spent on Day 1 of operation.

Although embodied carbon is a fairly new concept, organizations like Architecture 2030 and BuildingGreen, as well as others, are working to quantify its global impacts. Right now, the built environment (operational + embodied) is estimated to be responsible for almost 40% of our planet’s human-made annual CO₂ emissions. Keep in mind that this statistic includes many older buildings that are likely using exponentially more energy than the new building next door. As designers and operators continue to find ways to reduce building energy use, the scales will begin to shift, and embodied carbon will become the main culprit in built environment emissions. To meet the goals of the Paris Agreement and prevent the worst effects of climate change, embodied carbon must be part of the conversation. It is estimated that for all new construction between now and 2050, embodied carbon will account for 90% of resulting CO₂ emissions.

While every material used contributes in some way to the final embodied carbon count, research has shown that structural systems in a building have the largest impact. Concrete and steel together, which most structural systems utilize in some way, account for 11% of global CO₂ emissions. The primary factors that lead these materials to have high embodied carbon counts are the manufacturing process used to create the final building material involves large amounts of combustion, the cleanliness (or lack thereof) of the energy grid supporting the manufacturing plant and the proximity of the manufacturing location to the site.

The good news is that, once a team starts using this attribute as a criteria for material selection, it is possible to make dramatic reductions in the embodied carbon content of new building and renovation projects. Evaluating the enclosure systems, particularly the window-to-wall ratios and the enclosure materials themselves, will further reduce the embodied carbon content. Where there traditionally has not been a significant role for structural engineers in the world of sustainability, they can now step into the forefront as pioneers toward decarbonizing the built environment.

Employing an order of operations in material selection can help simplify the process. Utilizing existing buildings to avoid new construction, using less material and reusing materials where possible are great places to start. The reality, though, is that material selection will likely play a significant role in any project. Product certification programs, such as the Environmental Product Declaration, provide information on embodied carbon content that can aid in material selection. Where information is not available, the design industry can use the opportunity to push vendors to be more transparent, which will enable teams to make informed decisions.

So, how do we move forward into a world of designing buildings with low embodied carbon? For starters, to steal a phrase from embodied’s sister, operational carbon: You can’t manage what you don’t measure. Using the processes already well-established for reducing operational carbon, design teams should set a whole carbon (operational + embodied) goal early on that creates a roadmap for the design team as they move forward. Just as design teams use an energy model throughout the design process for tracking the energy use of proposed buildings, teams should utilize a whole-building, life-cycle analysis tool to track the embodied carbon of the design. And holding the final design accountable for achieving the early target will demonstrate that designing toward reduced embodied carbon is achievable within a budget.

The science around embodied carbon is new and ever-changing. However, understanding the significant role it plays in global CO₂ emissions is the first step toward further reducing the environmental impact of the buildings we design. The concept of reducing the global impact of our designs is not new. The opportunity to apply learned skills towards new effects has the potential to be revolutionary.

For more great sustainability information, contact Kristy Walson, PE, LEED AP BD+C, LEED AP O+M, BEMP at kristy.walson@tlc-eng.com or 407.487.1118.