At Carbon Title, we have a commitment to a scientifically rigorous calculation of carbon emissions that stands up to scrutiny. The scope and methodology used in reaching our calculations is below. As we update and further refine the model, we will continue to update these materials. Please direct any questions to info@carbontitle.com.
Whole Life Carbon
The Carbon Title Calculator is an whole life carbon model. "Whole life carbon" means that it integrates assessments of embodied, operational, and landscape carbon in a data model to capture the entire carbon footprint of the project.
Time Horizon
The Carbon Title Calculator uses a 30-year time horizon.
Life Cycle Stages:
The Carbon Title Calculator integrates data from life cycle stages (sometimes called "life cycle modules") A1-A5, B2-B6, and C2-C4. These correspond to the impacts of the materials used in the project, emissions from construction, their replacement over time, and the project’s operational energy use. When biogenic carbon is counted, some end-of-life impacts (from modules C2-C4) are assessed during the product phase. End-of-life (C2-C4) emissions for structure are only assessed when a 60 year time horizon is selected.
Embodied Carbon Scope
The Carbon Title Calculator considers embodied carbon from a number of sources. Its scope may be distinct from other tools.
Operational Carbon Scope
The Carbon Title Calculator considers operational emissions from the following sources:
Stored Carbon Scope
The Carbon Title Calculator includes an estimate of carbon storage in timber structural systems and site landscaping. Carbon storage in planting is calculated over the time horizon then annualized. Carbon storage in building structure is assigned to the first year of the project.
Anecdotal evidence has put The Carbon Title Calculator results (modeled without any customization) within 5-30% of the estimates generated by whole building Life Cycle Assessment.
Calculating Embodied Carbon
For each contributor i, embodied emissions assessed by the Carbon Title Calculator are evaluated with the following expression:
Where A is the total building area, xi is the quantity of the contributor i per building area, and ci is the carbon intensity per unit of the contributor i.
For example, a 10,000 sf building may use 4 pounds of reinforcing steel per square foot of floor area, and the reinforcing steel may have a carbon intensity of 500 grams (0.5 kilograms) of carbon dioxide-equivalent emissions per pound of steel (not actual values and for illustrative purposes only). Taking the product of these three hypothetical quantities yields the contribution of reinforcing steel to that building's embodied carbon emission:
In each part of its model, the Carbon Title Calculator sums the assessed emission of many individual contributors. While simple summation is acceptable in some cases, some materials will be replaced before the target date. For these materials, the emissions are assigned to the year(s) in which they're replaced, and a multiplier is added to the total summation. The total embodied emissions assessed by Carbon Title/EPIC are represented by this expression:
For n number of contributors to the embodied emissions, where A is the total building area, xi is the quantity of the contributor i per building area, ci is the carbon intensity per unit of the contributor i, and ri is the number of replacements of the contributor i before the target date.
Calculating Operational Carbon
The operational emissions of the project are assessed annually and summed across all years before the target date. The equation is similar to the equation for embodied emissions, with two key differences: first, the quantity x is substituted for the energy use intensity (EUI) e; second, the equation is a double summation, once across all the fuel types in the building and again across all years between the building's completion and the target year. The total operational emissions assessed by the Carbon Title Calculator are represented by this expression:
For m total years between the building's completion and the target year and across o fuel types, where A is the total building area, etj is the energy use per building area (EUI) in year t of fuel j, and ctj is the carbon intensity per energy unit in year t of fuel j.
Calculating Stored and Avoided Carbon
In the Carbon Title Calculator, landscaping and the use of structural timber contribute to biogenic carbon storage. Carbon storage in structural materials is assessed once in the first year of the project, and landscape sequestration is assessed each year. Biogenic carbon sequestration is evaluated with the following expression:
Where xi is the amount of carbon-sequestering timber structural material i, Ci is the carbon sequestration per unit i, is the area A of carbon-sequestering planting type k, and Ck is the carbon sequestration in year t per area of planting k.
The generation of excess energy by an onsite solar photovoltaic array displaces the generation an equivalent amount of electricity from the utility grid. This is calculated as follows:
Where et is the excess energy in kWh generated in year t and ct is the carbon intensity of the electrical grid per unit demand in year t. This method assumes that there is no curtailment of PV production, and that the carbon emissions of grid electricity when solar energy is produced is substantially similar to the annual average emissions. In locations with a high proportion of solar on the grid, curtailment is likely and skepticism of c.scale's calculation of avoided emissions is warranted.
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Note:
The Carbon Title Calculator is developed in collaboration with a third party carbon calculation model, c.scale, developed by climate scientists and a world-renowned architectural firm, EHDD. For more information, please contact us at info@carbontitle.com.
