I'm an engineer that frequently sizes natural gas piping systems. I typically use the longest length method and the sizing tables in the IFGC Chapter 4. Recently I've been putting together a spreadsheet to help expedite sizing, and thought I would use the high-pressure gas equation to calculate the sizing.
As far as I can tell, all my assumptions are identical to the table: smooth Schedule 40 pipe, 1 psi drop from 2 psig inlet to 1 psig outlet.
I can't seem to use the tables to "check" the equations, per se, because the results come out so different. Most concerning, when I change it to Undiluted Propane and plug in those equation factors, the results are much, much further off. I've double and triple checked the math, read the appendices for additional assumptions, but I've come to my wits end.
To provide an example of the stark contrast:
For Undiluted Propane, at 2psig with 1 psig pressure drop, Schedule 40 pipe, 200 ft. length, through 2" diameter pipe.
Sizing Table 402.4(27) gives a capacity of 12,300 MBH.
However, with those same assumptions, the High-Pressure gas equation (Equation 4-2) gives a capacity (input rate) of 4,580 MBH.
That is a huge difference and a cause for concern. What am I missing here? My instinct tells me I've made a math error but I can only check so many times.
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