**Q753. How do I use Equation C-2b to calculate the annual average high heating value (HHV) of my fuel if the rule requires sampling less frequently than monthly?**

**A753.**

Example 1: Natural gas fuel is sampled semiannually and the results for the first and second semiannual periods are 1,020 Btu/scf and 980 Btu/scf, respectively, and the respective semiannual fuel quantities are 1,000 scf and 2,500 scf. You would calculate the annual average HHV using Equation C-2b as follows: You use the HHV and fuel quantity values that represent the less frequent sampling period (i.e. quarterly, semiannually) in place of the monthly values that are normally used in Equation C-2b. Two examples are provided below.

(HHV)annual = [((1,020 Btu/scf) x (1,000 scf) + (980 Btu/scf) x (2,500 scf))/3,500 scf] = 991 Btu/scf

Example 2: Everything is the same as in Example 1 except that you missed sampling during the first semiannual period. In this situation, the missing data procedures would apply. Per 98.35(b)(1), you would substitute, for the missing value, the arithmetic average of the quality-assured values of the HHV immediately preceding and immediately following the missing data incident. If the HHV was 1,000 Btu/scf for the second semiannual period during the prior year and the HHV for the second semiannual period during the current year Is 980 Btu/scf, the substitute HHV used for the first semiannual period of the current year would be the arithmetic average of 1,000 Btu/scf and 980 Btu/scf, or 990 Btu/scf. You would then calculate the annual average HHV using Equation C-2b as follows:

(HHV)annual = [((990 Btu/scf) x (1,000 scf) + (980 Btu/scf) x (2,500 scf))/3,500 scf] = 983 Btu/scf

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