UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C.  20460

        OFFICE OF 

AIR AND RADIATION

June 10, 2010

MEMORANDUM

SUBJECT:	Example Workbook Calculating the Error of the Mass-Balance
Approach in

Estimating Fluorinated GHG Emissions from Fluorinated GHG Production

FROM:	Deborah Ottinger

		Climate Change Division

TO:		The Record

Under the proposed rule for Mandatory Reporting of Greenhouse Gases:
Additional Sources of Fluorinated GHGs, facilities interested in
pursuing the mass-balance approach to estimate their fluorinated GHG
emissions from fluorinated GHG production would have to be able to
demonstrate that their process measurements and calculations passed an
error test (75 FR 18652, April 12, 2010).  Calculations for the test are
included in the proposed rule.  The workbook entitled “Example Mass
Balance Error Calculation.xls” illustrates how the error calculation
might work with one well-known production process.  

This workbook was developed as a "proof of concept," not an actual
calculation tool.  If EPA finalizes the error test for the mass-balance
approach, the Agency will provide a more user-friendly tool that will
include instructions and background.  Nevertheless, by working through
the spreadsheets and referring to the corresponding equations in the
proposed subpart L regulatory text, one can see how the error test could
be implemented.

There are four spreadsheets in the workbook.  The first two contain the
calculations of interest for the two reactants (one spreadsheet per
reactant).  The third and fourth provide background on the reaction and
ensure that the masses will actually balance.  A facility wouldn't need
the third spreadsheet to calculate the error for an actual process
because the relevant values would be measured rather than calculated.

To see how the first two spreadsheets work, spreadsheet users should
refer to the equations in the proposed regulatory text whose numbers
appear in the heading of each group of columns.  In general, the
equations appear in the sheet in the order that a facility would solve
them to calculate its emissions.  Within each equation, the columns on
the left side are the inputs, and the last column is the output.  The
values that are calculated using the mass-balance equations (and error
propagation equations) appear in purple.  (Since the spreadsheet is just
a model, it also calculates some of the input values that appear in
black, but they would be measured in an actual process.)  The
calculations proceed from left to right and down.  The outputs of some
equations are used as the inputs for the next, both for the emissions
calculation and for the error calculation.  

The values for the percentages of products and by-products in various
streams are hypothetical.  Users of the spreadsheet can adjust these,
but they should take care to ensure that they are accounting for all
masses and flows (e.g., make sure the percentages of the by-product
going to the various process streams don't add up to more than 100%).   

One important note: the spreadsheet uses the example of HCFC-22 with
HFC-23 as the by-product because this is a widely known reaction.  The
workbook calculates both HCFC-22 emissions (the product) and HFC-23
emissions (the by-product).  However, HCFC-22 production is actually
covered by subpart O rather than subpart L, and only the HFC-23
emissions, not the HCFC-22 emissions, are covered by subpart O.
Nevertheless, the basic math and logic should be the same for the
processes covered by subpart L.

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