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BEopt Gas carbon factor & source to site ratio interplay

asked 2023-07-31 12:54:06 -0500

jpierce's avatar

updated 2023-07-31 15:39:41 -0500

How exactly are these used when calculating emissions, specifically fugitive emissions?

The BEopt 2.8 help says:

The default value is a national average of pounds of equivalent carbon dioxide released per unit of fuel, as published in ANSI/ASHRAE Standard 105-2014, Appendix J. Equivalent CO2 is calculated using 100-year time horizon global warming potential (GWP) values for CO2, NOx, and methane emissions.

This implies that this number already has some methane leakage accounted for, presumably in production. However, Table 4 of "Operational Emissions Accounting for Commercial Buildings" <https://www.nrel.gov/docs/fy22osti/81... > says that the newest standard (105-2021) is "full life cycle"… which could be read to include distribution.

The BEopt 3.0b help gives the following, which is what one would expect:

Values greater than 1 are typically used to account for losses occurred in pipeline transmission and distribution of the fuel.

But how are the emissions for over-unity source:site ratio (distribution losses) handled? A ratio of 1.05 would imply 5% natural gas leakage. Does the software have a baked-in natural gas to CO2e conversion that applies for those excess therms? Because the same factor as applied for the delivered energy does not seem correct, since there is no combustion of the lost gas, and depending on what is meant by "full life cycle", the source:site ratio may have overlap with the carbon factor.

P.S. What is the source of the default natural gas carbon factor in the 3.0 beta? It's 4% higher than the ASHRAE 105-2015 Appendix J value used in v2.8

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answered 2023-07-31 17:26:56 -0500

updated 2023-07-31 17:29:31 -0500

Here's what I know about the sources for carbon/source factors in BEopt v3:

CO2 Emissions

Source Energy

  • Electricity: Home Energy Score, using EIA Monthly Energy Review data with Captured Energy assumptions for Renewable Energy sources
  • Fossil Fuels: Home Energy Score, using I don't know what

There is no direct link between carbon and source factors, they have been developed independently. For example, the electricity carbon factors include future projections about the grid, but the source energy factors do not. It's frustrating that there is not more consistency between the various calculation methodologies. That said, there's no single way to do these calculations and reasonable people may disagree about assumptions.

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Thank you for the response. To clarify my original query about the interplay for future readers:

  • Source:Site = (Delivered + Fugitive) / Delivered
  • CO2e = Delivered Combustion CO2 + Fugitive * Methane GWP

It's the presence of fugitive in both that makes it seem ouroborosian, but I suppose if the carbon factor is based on/applied to site consumption rather than source consumption it should work out fine.

jpierce's avatar jpierce  ( 2023-08-01 07:55:54 -0500 )edit

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Asked: 2023-07-31 12:54:06 -0500

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Last updated: Jul 31 '23