Understanding the operational carbon function

Owned by Eana Bacchiocchi
Dec 11, 2023
6 min read

There is now operational carbon values attached to U.S. based projects created in 2023 and beyond. These values can be found on the top right of your project’s green summary box.

Methodology

The methodology for calculating GHG emissions in the AIA 2030 DDx is the same methodology that is used in Portfolio Manager.1 The methodology is based on the Greenhouse Gas Protocol Corporate Accounting and Reporting Standard developed by the World Resources Institute (WRI) and World Business Council for Sustainable Development.2 This protocol was developed as the accounting framework to provide a relevant, complete, consistent and transparent account of an organization’s GHG emissions. As the global standard, it serves as the basis for the accounting, inventory and reporting guidance provided by the Environmental Protection Agency’s (EPA) Center for Corporate Climate Leadership, as well as state and non-governmental organization registry, reporting, and recognition programs. 

No additional inputs are required to be entered into the AIA 2030 DDx to calculate the project’s operational carbon.  The calculation methodology adapts to the level of detail for the project data entered.  Examples include: 

  • eGrid subregion: determined by the project postal code 

  • Project region: determined by the project State or Province  

  • % Electricity:  determined by the primary project use type and region  

  • % Natural Gas:  determined by  subtracting the The “Percent Electricity” from 100%  

  • % Net pEUI reduction savings:  determined by the code equivalent savings associated with the project’s design energy code. 

  • Net pEUI (kBtu/sf):  determined by multiplying the baseline EUI by (1 – code equivalent savings)  

  • Predicted Annual Energy Consumption (kBtu):  determined by multiplying the “Net pEUI” (kbtu/sf) by the “GSF (sf)”  

  • Electrical and Natural Gas Energy (MBtu):  The operational energy (kBtu) is multiplied by the “Percent Electricity” to determine the “Electricity Energy”, and the same approach is used to calculate “Natural Gas Energy”.  Both are converted to MBtu units. 

  • Emissions Factors:  The Electricity and Natural Gas emissions factors (kg CO2e / Mbtu) are determined using the eGrid subregion 

  • Electricity Emissions (CO2e):  The “Electricity Energy (Mbtu)” is multiplied by the “Electricity Emissions Factor (kg CO2e / Mbtu)”  

  • Natural Gas Emissions (CO2e):  The “Percent Natural Gas (Mbtu)” is multiplied by the “Natural Gas Emissions Factor”  

  • Operational Carbon Emissions (CO2e): The “Electricity CO2e” and “Natural Gas CO2e” are added together  

  • Operational Carbon CO2e intensity (CO2e/sf):  The “Operational Carbon CO2e” is divided by “GSF sf)”  

  • Note:  No renewables are associated with this project type. 

The calculations follow the same steps as above to the point where the Net pEUI (kBtu/sf) is being calculated.  In this case, the “Gross pEUI” and “Net pEUI” have been entered, so the “Predicted Annual Energy Consumption” is known.   

  • Predicted Annual Energy Consumption (kBtu):  determined by multiplying the “Net pEUI” (kbtu/sf) by the “GSF (sf)”  

  • Electrical and Natural Gas Energy (MBtu):  The operational energy (kBtu) is multiplied by the “Percent Electricity” to determine the “Electricity Energy”, and the same approach is used to calculate “Natural Gas Energy”.  Both are converted to MBtu units. 

  • Emissions Factors:  The Electricity, Natural Gas, and Renewable Avoided emissions factors (kg CO2e / Mbtu) are determined using the eGrid subregion 

  • Electricity Emissions (CO2e):  The “Electricity Energy (Mbtu)” is multiplied by the “Electricity Emissions Factor (kg CO2e / Mbtu)”  

  • Natural Gas Emissions (CO2e):  The “Percent Natural Gas (Mbtu)” is multiplied by the “Natural Gas Emissions Factor”  

  • Renewable Energy Avoided Emissions(CO2e):     

    • Gross pEUI” – “Net pEUI” yields “Renewable Contribution pEUI (kBtu/sf)”.  

    • The value is multiplied by “GSF (sf)”, and then converted to MBtu. 

    • Next, it is multiplied by the “Renewable Avoided Emissions Factor (kg CO2e / MBtu) to determine “Renewable Energy Avoided Emissions(CO2e)” 

  • Operational Carbon Emissions (CO2e): determined by: 

    • “Total Electricity CO2e” = “Electricity CO2e” - “Renewable Energy Avoided Emissions(CO2e)” 

    • Note:  if “Renewable Energy Avoided Emissions(CO2e)” > “Electricity CO2e”, the result is “0”.  The “Total Electricity CO2e” cannot be negative. 

    • Operational Carbon Emissions (CO2e) = “Natural Gas CO2e” + “Total Electricity CO2e” 

    • Operational Carbon CO2e intensity (CO2e/sf):  The “Operational Carbon Emissions CO2e” is divided by “GSF (sf)”  

In this case the energy (Mbtu) for each fuel source does not need to be calculated because it has already been entered and/or imported. 

  • Emissions Factors:  The emissions factors (kg CO2e / Mbtu) are determined using the eGrid subregion 

  • Electricity Emissions (CO2e):  The “Electricity Energy (Mbtu)” is multiplied by the “Electricity Emissions Factor (kg CO2e / Mbtu)”  

  • Natural Gas Emissions (CO2e):  The “Percent Natural Gas (Mbtu)” is multiplied by the “Natural Gas Emissions Factor” 

  • Renewable Energy Avoided Emissions(CO2e):    

    • “Gross pEUI” – “Net pEUI” yields “Renewable Contribution pEUI (kBtu/sf)”.  

    • The value is multiplied by “GSF (sf)”, and then converted to MBtu. 

    • Next, it is multiplied by the “Renewable Avoided Emissions Factor (kg CO2e / MBtu) to determine “Renewable Energy Avoided Emissions(CO2e)” 

  • Operational Carbon Emissions (CO2e): determined by: 

    • “Total Electricity CO2e” = “Electricity CO2e” - “Renewable Energy Avoided Emissions(CO2e)” 

    • Note:  if “Renewable Energy Avoided Emissions(CO2e)” > “Electricity CO2e”, the result is “0”.  The “Total Electricity CO2e” cannot be negative. 

    • Operational Carbon Emissions (CO2e) = “Natural Gas CO2e” + “Total Electricity CO2e” 

    • Operational Carbon CO2e intensity (CO2e/sf):  The “Operational Carbon Emissions CO2e” is divided by “GSF (sf)”  

FAQs

Why aren’t I see operational carbon values on my non-U.S. based projects?

Unfortunately, at this time, the DDx is only able to calculate operational carbon emissions for U.S.-based projects.

Why are the operational carbon values different for ‘Grid Electricity’ and ‘Electricity from on-site renewables’?  Shouldn’t they be the same? 

Scenario:  I’ve entered similar fuel source kWh values for ‘Grid electricity’ and ‘Electricity from on-site renewables”, but when I look at the Net Operational Carbon table, particularly the electricity column, the operational carbon value for the renewables is significantly higher?  Shouldn’t they be the same?  

Short answer:  No.  They each have different emissions factors, and the avoided emissions from on-site renewables will make that value higher.   

One way to think about why there is a difference, is to think about where the kWh of electricity being used by the project is coming from: 

  • If it is from the grid (“Grid Electricity), then it has ‘losses’ associated with it, which includes generation, transmission, and distribution losses.  The ‘cleanliness of the grid’ establishes the CO2e Emissions (kg/MBtu) associated with that eGrid region.   

  • If it is from on-site renewables, then it has fewer ‘losses’ associated with it, and it means that kWh doesn’ t need to be delivered to the project by the grid.  This results in a higher CO2e Emissions (kg/Mbtu) factor for the project, but in this case it is a value for “Avoided Emissions”. 

An all-eletric project is located in Massachusetts.  The design energy performance for the project has predicted “Grid Electricity” consumption of 10,000,000 kWh and has predicted on-site renewable energy generation of 9,000,000 kWh.  Therefore, the renewable energy generation is 1M kWh less than the building electricity. 

  • eGrid Region:  The project’s postal code in Massachusetts identifies the eGrid region as NEWE. 

  • The GHG emissions factor for electricity for NEWE = 72.32 kg/MBtu 

  • The GHG avoided emissions factor for on-site renewables for NENE = 120.32  kg/MBtu 

Net Operational Energy Calculation 

Step 1:  Converting the kWh (multiply by 3.4121) for both to get kBtu/yr. 

Step 2:  Values inserted into the table 

Step 3:  Results - the project has a Net Operational Energy of 3.4 M kBtu/yr, which in this case (GSF=400k) equates to a Net Predicted EUI = 8.53 kbtu/sf/yr  

Net Operational Carbon Calculation 

Step 1:  Converting the kWh (multiply by 0.003412) for both to get MBtu/yr. 

Step 2:  Grid Electricity multiplied by NEWE emissions factor (72.32 kg/MBtu) 

Step 3:  On-site renewables value multiplied by NEWE avoided emissions factor (120.32  kg/MBtu) 

Step 4:  Values inserted into the table 

Step 5:  Results – since the avoided emissions factor for NEWE is higher than the electricity emissions factor, the avoided emissions for the renewables is larger (3.60 M kg CO2e) than the Building Electricity values (2.47 M kg CO2e).  However, the emissions total for the project is “0”, and not negative, because only 2.47 M kg CO2e avoided emissions can be associated with the project. 

If you want to read through the calculation methodology that Energy Star has established, read through the technical references for Greenhouse Gas Emissions1 and Green Power3.   

Things to keep in mind: 

  • Projects can have a negative Net predicted EUI (Energy positive, where on-site and/or dedicated renewables are larger than building energy), but have the Net Operational Carbon value be zero or greater than zero.