C.Scale

Carbon emission modeling in the Impact Building Calculator is performed via the C.Scale API, a whole life carbon data model for buildings. Full documentation on the methodology behind C.Scale is available here.

Operational Emissions

The Calculator includes operational emissions from two sources: the combustion of fossil fuels on the building site, and the upstream emissions incurred by electricity used by the building.

Fossil Fuel Emissions

Fossil fuel emissions are assessed on an annual basis as:

Where Emissionsf,i is the annual fossil fuel use of fuel type f in year i, Usef,i is the annual fossil fuel use of fuel type f in year i in units volume, CIff is the emissions from combustion per unit volume of fossil fuels, rleakage is the leakage rate of that fossil fuel (assumed to be 2.5% for natural gas), and GWP100,ff is the GWP-100 value for that fossil fuel when leaked directly into the atmosphere.

Cumulative fossil fuel emissions over the time series is:

Where m is the year of implementation and n is the target year.

In the Building Decarbonization Calculator, all on-site combustion is assumed to be natural gas.

Electricity Emissions

Upstream emissions from electricity use are assessed on an annual basis. Electricity demand from the asset each year is assumed to be constant, but the emissions associated that demand are expected to decrease over time as the electrical grid decarbonizes. Methods and data sources for determining the pace of utility grid decarbonization vary regionally:

• United States: C.Scale uses data from NREL Cambium 2024 to model emissions over time. These estimates are highly regionalized and reflect the local and national policy commitments, as well as techno-economic constraints. The Calculator uses Long-Run Marginal Emission Rates in the United States, the metric most appropriate for modeling emissions from long duration loads (e.g. like that incurred by buildings).

• Australia: C.Scale uses present-day electrical grid emissions from data provided by the Australian Energy Market Operator. As of 2024, Australia is developing a 2050 Net Zero Plan, but it is not yet published.

• Canada: C.Scale uses a similar method to incorporating U.S. Grid Data was employed. Using measured Grid Data and future projection data, yearly Canadian Grid emissions are estimated through 2110 so that operational emissions of any C.Scale project started before 2050 can be effectively estimated over a 60 year lifetime.

• EU: C.Scale uses present-day grid emission factors from the European Environment Agency. These metrics are different for each country. We assume that all EU countries will decarbonize their electrical grids to converge of full decarbonization of the power sector by 2050.

• Saudi Arabia: C.Scale uses present-day grid emission factors from EMBER. Saudi Arabia has a goal of a net zero economy by 2060, but data is not published on emissions rates on a kWh-basis.

• Singapore: C.Scale uses present-day grid emission factors from EMA. Singapore has a goal of a net zero electricity sector by 2045.

• UAE: The UAE has a plan to achieve a electricity grid carbon intensity of 0.27 kgCO2e/kWh by the year 2030, and net zero by 2050. However, these plans indicate a percentage of gas and coal remaining on the grid in 2050, suggesting that the actual incurred emissions will not be zero.

• UK: C.Scale uses present-day grid emission factors from the UK Department for Energy Security and Net Zero. We assume that decarbonization of UK electricity supply will achieve the government's stated commitment of full decarbonization of the power sector by 2035.

• Electricity emissions over the time series are assessed as:

District Heating Emissions

In Nordic countries, the user can indicate the presence of a district heating system. Emissions associated with district heating are highly variable; the Calculator assumes a medium emissions intensity of 0.285 kgCO2e/kWh.

Embodied Emissions

"Embodied emissions" is common parlance for the upstream emissions associated with the manufacturing, transportation, and installation of materials in a buildings (as well as their maintenance over time). In the Building Decarbonization Calculator, embodied emissions are factored into the calculation in two ways:

• Embodied carbon of ECCMs. When an ECCM requires the installation of additional material (e.g., for envelope and glazing upgrades), the embodied emissions of this measure are calculated via the C.Scale API. For ECCMs associated with products from Schneider Electric, the relevant published environmental product data will be used to estimate the embodied carbon (to be incorporated into the Calculator in 2026).

• Embodied carbon of cyclic refurbishments. For commercial buildings, we assume a regular retrofit cycle which the interiors are refreshed every 15 years, MEP systems every 20 years, and the building envelope every 50 years. These regular replacement cycles give the carbon emissions time series charts their characteristic "stepping" pattern.