Leaders in sustainable real estate know how to optimize energy. The LEED rating system was built upon the premise that the polluting impact of energy consumption is the priority in making a greener building. In fact, total end-use energy consumption by the residential and commercial sectors was about 21 quadrillion British thermal units (Btu) in 2019, which equals 28% of total U.S. end-use energy consumption in that year (source).
While buildings used 28% of the energy in the U.S. in 2019, they released 39% of the carbon. That carbon was released in the form of operational emissions such as those from boilers and furnaces, water heaters, and onsite power generation. There are also indirect emissions such as those released from the carbon embodied in the building’s materials and construction processes.
There are a lot of carbon sources in addition to energy, and a successful carbon strategy must consider all factors that contribute to a building’s carbon footprint. If your climate strategy is limited to energy, you are neglecting your carbon emissions that also contribute to climate change.
One strategy for a project team to shift its approach from energy to carbon is to include carbon analysis in the project plan. Many of the best practices that have been established in energy modeling can be applied to carbon analysis. Most of these steps do not involve additional work other than communication with your design team.
If you are ready to include carbon in your next project’s strategy, here are some high-level best practices to guide you:
Determine the Carbon Metric: Choose a metric that the team can understand and then normalize it. One reason energy is a consistent metric across projects is because people can understand it; people can identify with a building EUI of 45, whereas 3,200 mt/CO2e might mean very little. EPA Greenhouse Gas Equivalencies Calculator can help the team to better understand how carbon metrics translate to real-world designs. We recently provided clients with a visualization of their carbon footprint by illustrating a “bubble” of carbon that was comparable to one of their buildings. Presenting a conceptual representation of 1 ton of carbon created “aha” moments by making the abstract concrete.
Brown University put this 32-foot tall balloon on campus for Earth Week to help students understand what one ton of CO2 looks like. (source)
Set a Design Target: Use the carbon metric to set a design target such as total operational carbon or percent carbon reduction. Benchmarking against similar buildings can help set goals and targets. ENERGY STAR Target Finder can be leveraged for this task. This process is similar to what we do with energy performance targets, and the process will be familiar to most teams, even if the carbon metric is new. Discuss carbon targets and goals during the eco-charette or project kick-off.
Determine Carbon Emission Factors: Most programs still evaluate performance based on energy, so carbon can be calculated by converting MBtu gas or electricity using CO2 emission factors. Three sources of these emissions factors are ENERGY STAR, utility providers, and Climate Registry. Your energy source impacts the carbon footprint of your energy. For example, the carbon footprint of 2000 kWh for a building powered by solar power will be very different from the carbon footprint of a building powered by coal.
Evaluate Operational Carbon: To evaluate operational carbon (the carbon load), you do not need to change the process that is used to evaluate energy, only the metric. During the design phase of a project, leverage the energy model to determine predicted carbon through the carbon emission conversion factors.
Evaluate Embodied Carbon: Embodied carbon accounts for the carbon included in the raw building materials harvesting, processing, transporting, etc. The calculation for embodied carbon is new to many, so you should focus on materials that have the largest carbon contribution to your buildings such as concrete, steel, glass façade, insulation, carpet, and ceiling tiles. Perform a whole building lifecycle assessment to predict the embodied carbon impact of these materials, similar to how project teams use energy models to predict operational carbon. Ensure that the Revit model is built for accuracy of materials tallying and maintain a bill of materials, collecting any Environmental Product Declarations (EPDs), to finetune and backcheck the predictive model.
Evaluate other emissions: You can further evaluate the carbon impact of a building or project by calculating other emissions such as carbon consumption through employee transportation. Tom Paladino wrote a great post about achieving Net Zero carbon with tips to address Scopes 1,2, and 3. You can read it here.
Make Design Decisions Based on Carbon Reductions: Make carbon a priority by setting carbon-based targets and establishing carbon as a primary decision factor. Every major project discussion should include the impact of a decision on the carbon target. And rather than evaluating pay-back based on energy cost, it can be based on carbon costs or carbon savings per conservation measure.
For example, one of our clients was interested in carbon reductions for their building, so all modeling deliverables were evaluated based on carbon. The energy model used total carbon and carbon savings over their ASHRAE baseline to evaluate conservation measures and operational building improvements.
Because total building performance was already being evaluated in carbon metrics, it was easy to layer on additional project carbon contributors such as embodied carbon of materials and refrigerant leakage. Evaluating carbon in terms of CO2e allowed us to calculate the greenhouse gas emissions of the building with one unit/one number based on the life cycle of the building.
Evaluate Carbon Offsets and Carbon Sequestration: There are also emerging technologies that find innovative ways to capture carbon in concrete – which you can read about in our blog post, Concrete, Cement, and Carbon. A carbon offset goes beyond your site to neutralize your carbon footprint through investment in outside projects such as renewable energy, landfill methane capture, livestock manure management, tree planting, or forest management improvement. Ensure that any offset project is verified by a third party.
The First Thing You Need to Do on Your Next Project:
Unfortunately, it’s not as simple as introducing a line item for carbon analysis to shift the team’s focus from energy to carbon. Energy-focused best practices have been built over generations as a result of shared knowledge and experimentation. But by beginning to introduce the vocabulary and normalizing the metric of carbon, we will get closer.
The most important thing that you must do is to include carbon as a priority for the project from day one by including carbon considerations in the RFP for the project team. Ask for project examples that showcase carbon innovation and make the carbon goals clear in the project overview.
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