Btu Factors (Heating Values) can be converted from Dry (natural gas not containing a significant amount of water) to Saturated (natural gas containing water) using the following formulas or conversion factors shown in Table 3. The .25636 factor used in the formulas and in the calculation of the table conversion factors is the vapor pressure of water at 60 degrees Fahrenheit as published in GPA Standard 2172-96.

General Rule: A Btu is a Btu regardless of whether the gas is Dry or Saturated.  Since water vapor will not burn or combust, natural gas of a given composition will contain fewer Btu per Cf if it is Saturated than it would contain if it were Dry.  Consequently, the Btu Factor for Saturated gas is less than the Btu Factor for the same gas if it were Dry.

Formulas:

Btu/Cf-Sat divided by (1 minus (.25636 divided by Pb) = Btu/Cf-Dry

Btu/Cf-Dry times (1 minus (.25636 divided by Pb) = Btu/Cf-Sat

Calculation Examples:

1000 Btu/Cf-Sat @14.65 divided by (1 minus (.25636 divided by 14.65) = 1018 Btu/Cf-Dry @14.65

1000 Btu/Cf-Sat @14.65 divided by .982501 = 1018 Btu/Cf-Dry @14.65

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Last updated on March 27, 2002