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Flow units - Natural Gas

Message 1 of 3
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Flow units - Natural Gas

I am trying to make a *working* natural gas system for MEP. For background info, I am using the Hydronic Supply System Classification. I have come across the issue where the project units are set to GPM, however I want this one system to use CFH. Also, when using the system inspector, I would really like to see my flows in CFH. I don't want to see the rest of the project in CFH because we also use GPM for domestic water flow rates. I know I can directly input CFH as 'xxx CFH' in the flow parameter - but it will simply convert it and tell me the flow in GPM. I can also set the pipe tags to force display CFH as the units so that my drawings read as intended.


For the Target/Source mechanical equipment, I can't pull 'Flow' into a schedule, so I put in a manual conversion to CFH as a shared parameter. This all works well, but for whatever reason, Revit only allows 3 significant digits in my conversion, muddying the water slightly. I want to retain use of Flow as a parameter to display on schedules, so I can count appliances and their demands automatically, as well as include it on plan for the City to look at.


Any suggestions or am I forced to convert back and forth at the equipment and system inspector level?

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Message 2 of 3


AU presentation which includes Natural Gas considerations, albeit somewhat old.

The presenter runs into the same sorts of challenges you're describing, their solution appears to be to make the CFH parameter unitless for readability. No mention of sig fig reduction, but I am curious if that necessarily comes up in pipe sizing - even if a 2" pipe at less than 2 Psi with 0.5" drop can carry 1160 CFH for 100 ft, I'd probably upsize to 2-1/2" when approaching that value just in case additional appliances or deviations in equipment submissions factor in.


Long story short, I don't believe Revit currently intuitively supports gas piping systems (or medical gas, compressed air, vacuum, etc.. specialty pipe systems). You can use the system inspector with a well-connected system, but I'd document the method of workaround if you have intentions on turning this over to a third-party contractor or consultant.

Message 3 of 3

Thanks for the insight. It's a shame that Revit doesn't do this inherently, it's one of the easiest calculations we do. They already do air calculations for HVAC...

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