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EXHIBIT 3-3: FACTORS TO CONSIDER WHEN EVALUATING UNCERTAINTY<br />

OF FLOW MEASUREMENTS USED FOR GHG EMISSION CALCULATIONS<br />

a) Confidence range of the measurement <strong>in</strong>strument<br />

− Manufacturers’ anticipated measurement errors for common flow meters could be used (Table 3-3) if on-site<br />

calibration data are not available<br />

b) Errors associated with “context-specific” factors<br />

Such factors may <strong>in</strong>clude the follow<strong>in</strong>g considerations:<br />

− Are measurement <strong>in</strong>struments <strong>in</strong>stalled accord<strong>in</strong>g to the manufacturer’s requirements?<br />

−<br />

−<br />

Is the measurement <strong>in</strong>strument designed for the medium (<strong>gas</strong>, liquid, solid substance) for which it is be<strong>in</strong>g<br />

used?<br />

If manufacturer’s data are not available, are the <strong>in</strong>struments operated accord<strong>in</strong>g to the general requirements<br />

applicable to that measurement pr<strong>in</strong>ciple?<br />

− Are there any other factors that can have adverse consequences on the <strong>uncerta<strong>in</strong>ty</strong> of the measurement<br />

<strong>in</strong>strument? (i.e., how the measurement <strong>in</strong>strument is used <strong>in</strong> practice).<br />

c) Pressure <strong>and</strong> temperature corrections for <strong>gas</strong> meters<br />

−<br />

Pressure <strong>and</strong> temperature corrections are only applicable to the determ<strong>in</strong>ation of the amount of <strong>gas</strong> <strong>and</strong> not to<br />

the measurement of liquids or solid substances.<br />

− The actual amount of <strong>gas</strong> flow has to be corrected for pressure <strong>and</strong> temperature to the specified st<strong>and</strong>ard<br />

conditions <strong>in</strong> order to avoid major systematic errors.<br />

d) Determ<strong>in</strong>ation of total uncerta<strong>in</strong>ties<br />

−<br />

Individual uncerta<strong>in</strong>ties determ<strong>in</strong>ed <strong>in</strong> a), b), <strong>and</strong> c) above ought to be summed up to determ<strong>in</strong>e the total<br />

<strong>uncerta<strong>in</strong>ty</strong> of the <strong>in</strong>dividual quantity measured.<br />

The discussion above perta<strong>in</strong>s to s<strong>in</strong>gle flow measur<strong>in</strong>g device <strong>uncerta<strong>in</strong>ty</strong>. Additional analyses are<br />

required to convert this <strong>in</strong>dividual measurement <strong>uncerta<strong>in</strong>ty</strong> to an assessment of the <strong>uncerta<strong>in</strong>ty</strong> range of<br />

annual measurements. Detailed guidance on the calculation steps is provided <strong>in</strong> Section 4.<br />

3.3 Uncerta<strong>in</strong>ties of Sampl<strong>in</strong>g <strong>and</strong> Analysis for GHG Emissions<br />

The emission measurement process comprises either direct measurement at the source level of collection<br />

of samples <strong>and</strong> their analysis <strong>in</strong> the laboratory to determ<strong>in</strong>e mass emissions. Sampl<strong>in</strong>g <strong>and</strong> analysis are<br />

part of the same measurement process <strong>and</strong> their comb<strong>in</strong>ed contribution to emissions estimation<br />

<strong>uncerta<strong>in</strong>ty</strong> is obta<strong>in</strong>ed by their comb<strong>in</strong>ed variances, as detailed <strong>in</strong> Section 4.0. Emission measurement<br />

uncerta<strong>in</strong>ties for processes of sampl<strong>in</strong>g <strong>and</strong> analysis depend on r<strong>and</strong>om errors, measurement precision,<br />

<strong>and</strong> systematic errors or bias.<br />

3.3.1 Gaseous Samples Collection <strong>and</strong> H<strong>and</strong>l<strong>in</strong>g<br />

Proper collection <strong>and</strong> h<strong>and</strong>l<strong>in</strong>g of <strong>natural</strong> <strong>gas</strong> samples could have a major impact on the accuracy <strong>and</strong><br />

representativeness of the analytical measurements based on these samples. Analyses of <strong>gas</strong> samples are<br />

used for multiple purposes <strong>and</strong> are applied to a variety of calculations <strong>in</strong>clud<strong>in</strong>g determ<strong>in</strong>ation of heat<strong>in</strong>g<br />

Pilot Version, September 2009 3-13

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