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Starch and Fiber Ethanol Calculator

Global Warming Potentials
Although the manual for the calculator says that global warming
potentials of greenhouse gases can be found on the Predefined
Inputs worksheet, these values seem to be missing. Not having
global warming potentials for reference made it somewhat difficult
to verify other parts of the calculator.

The most recent GWP values listed in GREET 2022 are from the 6th
IPCC Assessment (AR6) for N2O, CH4, and CO2. In case AR6 values are
not adopted, it should be noted that that the AR5 GWP-100 for
methane is listed incorrectly in GREET 2022 as 30. The published
value from IPCC is 28.

Corn Feedstock
The value assigned to corn farming in the new calculator is 6,945 g
CO2e/bushel, with GREET 2022 cited as the source. However, the
default value in GREET 2022 is just 6,762 g/bu. This value can be
found by either summing all non-transportation GHG emissions from
corn farming (EtOH tab, Table 3, cells C518:I528, plus the
miscellaneous N2O and CO2 emissions listed below these value) and
multiplying by AR6 GWPs, or more simply by checking the default
corn farming value in the 2022 GREET Feedstock Carbon Intensity
Calculator (FD-CIC). Both methods will give 6,762 g/bu.

Since the previous version of the Tier 1 calculator included
emissions from VOC, CO, and NO2, we assumed that the discrepancy
could be due to these additional GHGs, which have GWPs of zero by
default in GREET 2022. However, even after trying various sets of
GREET 2022 GWPs for these other gases we were unable to verify the
6,945 g/bu value.

It would be greatly appreciated to show the reference and
calculation of how the corn farming emission value was derived
and/or where it came from in GREET 2022, especially given that the
corn farming emissions factor is one of the few emission factors in
the calculator that has increased. Listing the GWPs that were used
for the calculator as well as a more specific reference to the
GREET 2022 model would help clarify this emission factor for corn.

Chemicals Usage
We noticed that the chemical usage emission factor in the current
calculator accounts for the EtOH feedstock and fuel loss factor. 
The new workbook doesn't account for this factor.  The amount is
negligible.

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Date and Time Comment Was Submitted: 2023-05-31 14:17:13