Operational carbon is often presented side by side with embodied carbon to weigh the impact of high performing operational-energy focused decisions against low-carbon design options. Tying operational energy results from the Baseline Energy Page into the Carbon Feature allows you to create these types of comparative studies.
As part of a lifecycle assessment (LCA), Module B6 - Operational Energy uses results the Baseline Energy Model to calculate operational energy, and then project that forward to account for grid decarbonization and building electrification over the estimated building life. You can read more about the tradeoffs between operational and embodied carbon in this blog post.
How is this helpful for your projects?
Design decisions often have impacts for both operational and embodied carbon. Here are some examples:
Single, double, or triple pane glazing
Impact of on-site renewables (PVs, solar hot water collectors)
Thermal performance of wall and roof assemblies
Glazing treatments, like tints, films, and low-E coatings.
...and many more! Any decision that changes the materials in a project AND impacts the energy consumption should be considered here.
Operational carbon is based on the electricity and gas consumption of a building during its operational life. These values are calculated as part of the Baseline Model in cove.tool. Once your model is calculated, these values are compared to a benchmark based on LEED requirements for the Energy and Atmosphere credits for energy reduction. As in the rest of the Carbon Feature, the inputs you select on the Baseline Model make up the “Achievable” carbon values, and the benchmark values make up the “Baseline” values.
Once the initial operational impacts have been calculated for both the baseline and the achievable scenarios, the Carbon Feature uses historical data on the carbon impact of electricity and gas, a decarbonization scenario, and the building life to estimate the total operational carbon over the course of the building’s operation.
In the Carbon Feature, you will see the baseline and achievable operational carbon side by side with the embodied carbon values. You can edit the initial grid factor and year as well as the gas consumption carbon factor in the Operational Carbon section of the Advanced Inputs panel.
The Baseline Model provides the annual operating energy and gas consumption for one year of operation. In the Carbon Feature, we pair that with impacts from grid decarbonization, future projects, and building electrification to estimate one potential scenario for operational carbon over the course of the building life.
Taking the annual consumption and system selection from the Baseline Model, the Carbon Feature uses the electric and gas consumption (kWh) to compare your inputs versus a standardized baseline defined by ASHRAE Standard 90.1-2010, Appendix G. The tool also looks at historical grid carbon emissions data (kgCO2e/kWh) and data from NREL and the CAMBIUM project in the US to determine the grid emissions projections based on the Decarbonization Scenario selected in the Carbon Feature. This scenario defines how the grid emissions will reduce over time. For instance, a 95% reduction in carbon emissions by 2050 is a typical projection, and the default in cove.tool.
Using those projections, the annual consumption is multiplied by that year’s projected grid emissions factor for electricity consumption, and a fixed factor for gas consumption (0.181 kgCO2e/kWh). At the 18th year of operation, it is assumed the building will be fully electrified, and any gas systems are replaced with electric equivalents. You can learn more about the equivalent systems here. The energy consumption is updated, and the projected values are calculated in the same way for the remainder of the building life. You can read more about grid decarbonization factors here.
Why am I seeing a negative operational carbon reduction?
If you are seeing a negative operational carbon value, it is typically because your baseline inputs are not performing better than the ASHRAE 2010 baseline. In the Baseline Energy Model, you can use the LEED Point Estimate result to get an idea of how much higher performing your project is before coming to the Carbon Feature.
What if my project location doesn’t have a grid carbon factor?
If your project location is one of the few that does not have a pre-populated grid carbon factor, you can manually enter the grid factor in the Advanced Inputs tab under the Operational Carbon section.