Carbon Emissions Calculations Explained

How Obi ESG calculates carbon emissions to present our absolute value and intensity consumption graphs

 

Calculations for Assets

The calculations required for consumption graphs at the asset level are based on three variables:

1. The consumption value uploaded to Obi ESG for an emission type. This value can apply for the entire asset, or can be uploaded to a specific submeter.
2. The emission factor for the emission type. This value is predefined for default emission types, but can be customised if the asset in question contains a submeter for the relevant emission type.
3. The total area of the asset.

Determining Emission Factors

The emission factor for each emission type is determined through different means. The relevant types are detailed below:

Heat/Gas

For heat/gas emissions, the emission factor value is fixed and does not change based on year or location. The fixed value is:

gas emission factor value = 0.18316 kgCO2e

This the carbon equivalent of burning 1 kg of natural gas (per CRREM)

Electricity

Electricity emissions have an emission factor that varies based on the year and the country that the asset is located in. For example, the below table shows the electricity emission factor values for Ireland between 2020 and 2024:

The change year-on-year is based on the decarbonisation pathway of each country, which affects the sustainability ratio of the electricity grid. 

Users have the option to use a custom emission factor for on-site generation etc. 

Water and Waste

Water and waste emissions are not yet considered in carbon emission calculations, and as such do not have relevant emissions factors.

Emission Calculations

1. Absolute Carbon Emissions

The formula for the calculation of absolute carbon emissions for a certain period of consumption and emission type is:

absolute carbon emissions (kgCO2e) = consumption value (kWh)
                                     * emission factor value (kgCO2e/kWh)

Note that this value is displayed in units of kgCO₂e, with the exception of the yearly absolute emissions graph, which is displayed in tCO₂e.

2. Carbon Emissions Intensity

The formula for the calculation of carbon emissions intensity is based off the calculated value for absolute carbon emissions:

carbon emissions intensity (kgCO2e/m2) = absolute carbon emissions (kgCO2e) / asset area (m2)

Note that carbon emissions intensity is always displayed in kgCO₂e/m².

3. Total Absolute Carbon Emissions

The total carbon emissions for the asset over a certain period is the sum of all the emission types:

total absolute carbon emissions (kgCO2e) = ∑ type 1 absolute carbon emissions (kgCO2e)
                                           + type 2 absolute carbon emissions (kgCO2e)
                                           + ...
                                           + type N absolute carbon emissions (kgCO2e)

4. Yearly Emissions

Calculating yearly emissions values for both absolute emissions is achieved by summing the values input for each period within the year. From here, emissions intensity is calculated by dividing by the asset area.

yearly absolute carbon emissions (kgCO2e) = ∑ Jan absolute carbon emissions (kgCO2e)
                                            + Feb absolute carbon emissions (kgCO2e)
                                            + ...
                                            + Dec absolute carbon emissions (kgCO2e)

yearly carbon emissions intensity (kgCO2e/m2) = yearly absolute carbon emissions (kgCO2e)
                                              / asset area (m2)

When yearly emissions are displayed in tonnes, as on the yearly absolute emissions graph, the calculation is a simple unit conversion:

yearly absolute carbon emissions (tCO2e) = yearly absolute carbon emissions (kgCO2e) / 1000

5. Scope Absolute Emissions

To calculate the absolute emissions for a scope, two types of carbon emissions values are considered:

1. emission types that are set to the scope by default (e.g. Gas is scope 1 by default), and
2. submeters that have been manually set to the scope. The total scope emissions are the sum of these two sums:

absolute emissions for scope N (kgCO2e) = ∑ default scope N absolute carbon emissions (kgCO2e)
                                        + ∑ submeter scope N absolute carbon emissions (kgCO2e)

6. Scope Intensity emissions

In order to calculate the intensity for each scope, the absolute carbon emissions for that scope are divided by the asset area:

scope N intensity emissions (kgCO2e/m2) = absolute emissions for scope N (kgCO2e)
                                        / asset area (m2)

7. Scope Yearly Emissions

Then, similar to absolute carbon emissions, the yearly value is the sum of the monthly values:

yearly scope N absolute carbon emissions (kgCO2e) = ∑ Jan scope N carbon emissions (kgCO2e)
                                                    + Feb scope carbon emissions (kgCO2e)
                                                    + ...
                                                    + Dec scope carbon emissions (kgCO2e)

The intensity value is the absolute value divided by the asset area:

yearly scope N intensity emissions (kgCO2e/m2) = yearly scope N absolute emissions (kgCO2e)
                                               / asset area (m2)

8. Scope Total Emissions

Unique to scope calculations is the total (all-time) emissions. The total absolute emissions by scope is then the sum of all these yearly values (from the baseline year onwards):

total absolute emissions by scope (tCO2e) = ∑ year 1 scope absolute carbon emissions (kgCO2e)
                                            + year 2 scope absolute carbon emissions (kgCO2e)
                                            + ...
                                            + year N scope absolute carbon emissions (kgCO2e)
                                            / 1000

Note that this value is displayed in tCO₂e, hence the conversion factor in the calculation.

Calculations for Fund

When calculating the absolute carbon emission and carbon emission intensity values for a fund, we use the sums of emissions from all assets within the fund.

9. Total fund Area

The total area for the fund is the sum of the areas of each asset:

total fund area (m2) = ∑ asset 1 area (m2)
                            + asset 2 area (m2)
                            + ...
                            + asset N area (m2)

10. Absolute Carbon Emissions

The absolute carbon emissions for a fund is the sum of each of the asset's absolute carbon emissions:

fund absolute carbon emissions (kgCO2e) = ∑ asset 1 absolute carbon emissions (kgCO2e) 
                                               + asset 2 absolute carbon emissions (kgCO2e)
                                               + ...
                                               + asset N absolute carbon emissions (kgCO2e)

11. Carbon Emissions Intensity

The carbon emissions intensity for the fund as a whole is the ratio of the previous calculations:

fund carbon emissions intensity (kgCO2e/m2) = fund absolute carbon emissions (kgCO2e)
                                                 / total fund area (m2)

12. Scoped Emissions

The emissions for each scope are the sum of the total emissions in that scope for each asset:

fund absolute emissions scope 1 (kgCO2e) = ∑ asset 1 scope 1 absolute carbon emissions (kgCO2e)
                                                + asset 2 scope 1 absolute carbon emissions (kgCO2e)
                                                + ...
                                                + asset N scope 1 absolute carbon emissions (kgCO2e)

Likewise, the intensity for the scope is the absolute value divided by the fund area:

fund emissions intensity scope 1 (kgCO2e/m2) = fund absolute emissions scope 1 (kgCO2e)
                                                  / fund area (m2)

 

Example Calculations

For this example, consider a fund with two assets: Asset A and Asset B.

Asset A (200 m²) contains:

• A default electricity meter (scope 2)
• A default gas meter (scope 1)

Asset B (300 m²)  contains:

• A default electricity meter (scope 2)
• A custom electricity submeter set to scope 3

Asset Emissions

Absolute Carbon Emissions - Asset A

Note that these examples do not show the summing of monthly values

Asset A - Electricity (see equation 1)

Asset A - Gas (see equation 1)

Asset A - Total (see equation 3)

Figure 1: Absolute carbon emissions per year for asset A

 

Carbon Emissions Intensity - Asset A

Asset A - By year (see equations 2 and 4)

Figure 2: Carbon emissions intensity per year for asset A

 

Emissions by Scope - Asset A

Asset A - Absolute by scope  (see equations 6, 7, 8)

Converted into tonnes:

Figure 3: Absolute emissions by Scope for asset A

Asset A - Intensity by scope total (see equations 6 and 7)

Figure 4: Emissions Intensity by Scope for asset A

 

 

Absolute Carbon Emissions - Asset B

Note that these examples do not show the summing of monthly values

Asset B - Electricity Default (see equation 1)

Asset B - Electricity Custom (see equation 1)

Year	Consumption Value (kW h)	Absolute Carbon Emissions (kgCO2e)
2023	18,100	18,100 * 0.29 = 5249
2024	15,000	15,000 * 0.271 = 4065

Asset B - Gas (see equation 1)

Asset B does not have any gas meters

Asset B - Total (see equation 3)

Note that because asset B only has electricity meters this is the same number as above

Figure 5: Total absolute carbon emissions per year for asset B

 

Carbon Emissions Intensity - Asset B

Asset B - By year (see equations 2 and 4)

Figure 6: Carbon emissions intensity per year for asset B

Emissions by Scope - Asset B

Asset B - Absolute by scope  (see equations 6, 7, 8)

Converted to tonnes:

Figure 7: Absolute emissions by scope for asset B

Asset B - Intensity by scope total (see equations 6 and 7)

Figure 8: Emissions intensity by Scope for asset B

Fund Emissions

Fund total area (m²) = 200 + 300 = 500 (see equation 9)

Fund - Absolute and intensity carbon emissions (see equations 10 and 11)

Figure 9: The absolute carbon emissions graph at the fund level

Fund - Scoped Emissions (see equation 12)

Scope	Absolute Emissions by Scope  (kgCO2e)	(tCO2e)	Emissions Intensity by Scope (kgCO2e/m2)
1	5119.322 + 0 = 5119.322	5.12	5119.322 / 500 = 10.24
2	8712.6 + 8331.3 = 17,043.9	17.04	17,043.9 / 500 = 34.09
3	0 + 9314 = 9314	9.31	9314 / 500 = 18.63

 

Figure 10: The emission by scope display a the fund level