ASHRAE Duct Pressure Loss

[Joe111222]

I have a duct 600x600 by about 15m long with 6 branches each at 600x300.

According to ASHRAE calculations, at 3200 l/s the main duct has a pressure loss of 1Pa and the branch itself (500 l/s) has a pressure loss of 63Pa.

This is the first branch and the 63Pa is higher than the full index run (to the end of the 15m 600x600 duct and last grille).

Do I change things to make the branch the main index run or ignore the 63Pa and keep the main index run as being to the last grille?

 

[berkshire]

The total of the branches on your duct are bigger than the main duct by a factor of three.
How are you going to balance and regulate this duct?
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[Joe111222]

Each branch has approx 500mm of duct and then the grille.

Branches will likely have VCD's or possibly stream splitter dampers.

 

[KiwiMace]

The index run is the run with the highest pressure drop. In a duct run with similar branch geometry this ends up being the last branch but it is not necessarily the case.

 

[willard3]

Find someone where you work who knows about ductwork.

You're not going to learn this on a web forum.

 

[berkshire]

With the type of duct you have described, you are either going to need sugar scoops in the main run, or you are going to have to throttle the branches enough to turn the main run into a plenum.

I think you need to seriously look at, either the size of the main run, and or the size of the branches. Or as Kiwi says you are going to find all of your air at the last register.
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor