Whole Life Carbon Assessment

C.Scale generates time series estimates of a building's carbon emissions and organizes those emissions by emission category and life cycle stage.

A1-3: Upstream Product Emissions

A1-A3 emissions are calculated from a bill of materials (e.g., life cycle inventory) inferred from the user's description of a building. The exact method for generating that bill of materials and calculating A1-A3 emissions varies by building assembly.

For each contributor $i$, embodied emissions in life cycle stages A1-A3 are assessed with the following expression:

$$Emissions_{A1-A3} = \sum_{i=1}^{n} Q_i \cdot EF_{A1-A3,i}$$

Where $Q_i$ is the quantity of material $i$ of all materials n, and $EF_{A1-A3,i}$ is the carbon intensity per unit of material $i$ for life cycle stages A1-A3.

A4-5: Construction Emissions

A4: Transportation of Materials to Site

All materials accounted for in A1-A3 must be transported to the site. C.Scale defaults to emission factors from the ASHRAE 240P draft guidance in table 6.5.2.1. These are conservative estimates of emissions per quantity of material. These data include a 0.5 return trip factor.

$$Emissions_{A4} = \sum_{i=1}^{n} \sum_{j=1}^{modes_i} M_i \cdot EF_{transport,j} \cdot D_{i,j}$$

Where $Emissions_{A4}$ is the total transportation emissions to jobsite, $M_i$ is the mass of material $i$, $EF_{transport,j}$ is the emission factor per ton-kilometer for transport mode j, $D_{i,j}$ is the distance for material $i$ using transport mode $j$, and $modes_i$ is the number of transport modes for material $i$.

A5.1: Pre-Construction Demolition

Pre-construction demolition emissions are calculated per floor area of the demolished building, using a default emissions factor from ASHRAE 240P (second draft for comments).

$$Emissions_{A5.1} = A_{demo} \cdot EF_{demolition}$$

Where $Emissions_{A5.1}$ is the emissions from pre-construction demolition, $A_{demo}$ is the area of pre-construction demolished building, and $EF_{demolition}$ is the emission factor per demolished area.

If fuel and electricity use data have been collected, it can also be used to calculate emissions from pre-construction demolition.

$$Emissions_{A5.1} = \sum_{k=1}^{p} Q_{fuel,k} \cdot EF_{fuel,k}$$

Where $Emissions_{A5.1}$ is the emissions from pre-construction demolition, $Q_{fuel,k}$ is the quantity of fuel type k used, $EF_{fuel,k}$ is the emission factor per unit of fuel type $k$, and $p$ is the number of fuel types.

A5.2: Jobsite Activities

Emissions from construction activities and land use change are included in A5.2.

Construction Activities

Construction activities include the use of tools, fuel, equipment, and energy on the building site. This includes site preparation, installation of materials, and other jobsite activities. When no additional data is provided, C.Scale usesa default emissions factor from ASHRAE 240P (second draft for comments) of project floor area.

$$Emissions_{A5.2} = A_{construction} \cdot EF_{construction}$$

Where $Emissions_{A5.2}$ is the emissions from construction activities, $A_{construction}$is the area of new construction, and $EF_{construction}$ is the emission factor per unit area for construction activities.

If fuel and electricity use data have been collected, it can also be used to calculate emissions from pre-construction demolition.

$$Emissions_{A5.2} = \sum_{k=1}^{p} Q_{construction,fuel,k} \cdot EF_{fuel,k}$$

Where $Emissions_{A5.2}$ is the emissions from construction activities, $Q_{construction,fuel,k}$ is the quantity of fuel type $k$ used for construction activities, $EF_{fuel,k}$is the emission factor per unit of fuel type $k$ , and $p$ is the number of fuel types.

Emissions from Greenfield Development

Land use change emissions from greenfield development are counted in A5.2. For details on land use change emissions, see Site and Landscape.

A5.3: Jobsite Waste

For each material and building assembly, C.Scale assumes a percentage of the installed total is wasted during construction. For all waste incurred during A5.3, we calculate A1-A4 and C2-C4 emissions for the wasted material and assign it to A5.3 emission for that material's category.

$$Emissions_{A5.3} = \sum_{i=1}^{n} (E_{A1-A3,i} + E_{A4,i} + E_{C2-C4,i}) \cdot Q_{installed,i} \cdot W_i$$

Where $Emissions_{A5.3}$ is the total emissions from construction waste, $E_{A1-A3,i}$ is the A1-A3 emissions for material $i$, $E_{A4,i}$ is the A4 emissions for material i, $E_{C2-C4,i}$ is the end-of-life emissions for material $i$ , $Q_{installed,i}$ is the quantity of material $i$ installed, $W_i$is the waste rate for material $i$, and $n$ is the total number of materials.

B Phase: Use Stage

The use stage includes all emissions from the operation of the building from the completion of construction until the end of the reference service period.

B1: In-Use Emissions

Fugitive emissions from annual refrigerant leakage, as well as refrigerant leakage for equipment replaced during the operating life of the building, are counted in life cycle stage B1. This is treated in detail in the documentation section on Refrigerant Emissions.

Annual carbon storage in the landscape is also included in this phase.

B2-B5: Replacement and Refurbishment

C.Scale uses a simplified model of replacement and refurbishment. For all materials in the C.Scale model, the emissions associated with this replacement and refurbishment—including manufacturing, transportation, and installation of the new materials, as well as end-of-life emissions for any removed materials—are assigned to the year(s) determined by the user-selected refurbishment period.

B4: Replacement Emissions

$$Emissions_{B4} = \sum_{i=1}^{n} \sum_{r=1}^{R_i} \left[ (E_{A1-A4,i} + E_{A5.3,i}) + E_{C2-C4,i} \right] \cdot P_{replacement,i,r}$$

Where $E_{B4}$ is the total emissions from replacement activities, $E_{A1-A4,i}$ is the upstream emissions for incoming material i (combining A1-A3 and A4 stages), $E_{A5.3,i}$ is the construction waste emissions for incoming material i, $E_{C2-C4,i}$ is the end-of-life emissions for outgoing material i, $P_{replacement,i,r}$ is the proportion of material i replaced in replacement event r, $R_i$ is the number of replacements for material i over building lifetime, and n is the total number of materials.

B6: Operational Energy use

Life cycle stage B6 includes operational emissions from energy use. This is treated in detail in the documentation section on Operational Carbon.

C Phase: End of Life

Data from life cycle stages C1-C4 cover the process from building demolition to the final disposition of materials as input to recycling, waste recovery processes, or landfills.

C1: Demolition

At early phases of design, C.Scale models C1 emissions following the guidance in ASHRAE 240P (second draft for comments), following the "business-as-usual" demolition scenario. This approach considers C1 emissions as a proportion of A5.2 emissions and calculates them on a per-area basis

$$Emissions_{C1} = A_{building} \cdot EF_{demo,area}$$

Where $E_{C1}$ is the emissions from end-of-life demolition, $A_{building}$ is the total building area, and $EF_{demo,area}$ is the emission factor per unit area for demolition activities.

If fuel and electricity use data have been more precisely estimated from future emissions, it can also be used to calculate emissions.

$$Emissions_{C1} = \sum_{k=1}^{p} Q_{EOL,fuel,k} \cdot EF_{fuel,k}$$

Where $E_{C1}$ is the emissions from end-of-life demolition, $Q_{EOL,fuel,k}$ is the quantity of fuel type k used for end-of-life demolition, $EF_{fuel,k}$ is the emission factor per unit of fuel type k, and p is the number of fuel types.

C1 also includes emissions from refrigerant leakage of all removed equipment.

C2: Transportation to End of Life Processing

BC.Scale's C2 model follows the same calculation approach as A4.

$$Emissions_{C2} = \sum_{i=1}^{n} \sum_{j=1}^{m_i} M_i \cdot EF_{transport,j} \cdot D_{EOL,i,j}$$

Where $E_{C2}$ is the total transportation emissions to end-of-life facilities, $M_i$ is the mass of material i, $EF_{transport,j}$ is the emission factor per ton-kilometer for transport mode j, $D_{EOL,i,j}$ is the distance for material i to end-of-life facility using transport mode j, $m_i$ is the number of transport modes for material i, and n is the total number of materials.

C3: Waste Processing for Recycling, Reuse, and Recovery

Data for life cycle stages C3 and C4 are collected from regionally-appropriate industry-average EPDs. Where data is unavailable in the US, EPA Warm and Sphera data area used as reference data sources.

$$Emissions_{C3-C4} = \sum_{i=1}^{n} Q_i \cdot EF_{C3-C4,i}$$

Where $E_{C3-C4}$ is the total emissions from end-of-life processing, $Q_i$ is the quantity of material i in declared unit, $EF_{C3-C4,i}$ is the emission factor per unit of material i for end-of-life processing in life cycle stages C3-C4, and n is the total number of materials.

D Phase: Benefits Beyond the System Boundary

The D phase of a whole life carbon assessment includes environmental benefits and burdens beyond the system boundary. D phase emissions are typically reported separately from life cycle impacts and should not be combined into a total emissions value for reporting purposes.

D1: Potential Benefits from Recycling, Recovery, and Reuse

Data for life cycle stage D1 are collected from regionally-appropriate industry-average EPDs. Where this data was not available, we assume D1 to be zero.

D2: Benefits from Exported Energy

If a building generates more energy than it uses in a given year and exports that energy to the grid, the benefit of this export can be declared in module D2 which counts the avoided impact of grid electricity generation. For more information, see Avoided Emissions.