Finding operating point for a system with multiple branches

[davidyu2404]

I am trying to locate the operating point for a multi-branch system. For the system curve, should I use a composite curve from all the branches or should I just use the critical path? Thanks!

 

[dbill74]

So long as the most remote outlet has sufficient pressure, everything else will too.

 

[RandomUserName]

Use your best judgement in finding the most restrictive path in your duct-work design (usually - but not always - your longest run). Calculate line by line friction and fitting losses from your unit to the most remote outlet. To confirm you selected the most restrictive run, compare other branches at the node where they connect. Only compare the branch in question from the connection point to its remote outlet to your original guess ... also from the connection point to the remote outlet. If the branch is more restrictive, it now is your new most restrictive path.

This most restrictive path ... everything is is balanced against and in proportion to it.

SMACNA Duct Design Guide has a good example problem in it.

 

[Ziggypump]

This is why you install balancing valves/dampers. The path of greatest resistance should (in theory) allow 100% flow. The path of least resistance will need added resistance to allow 100% flow to reach the greatest distance. If it is unclear on which path has the greatest flow, calculate all of them. The numbers will provide the answer.