JET DIFFUSER INSTALLATION!

[tcihvacff1]

Dear All, Greetings of the day!!!
I am dealing with a project where the height is double than normal. Its a showroom.
So we have plan to install a Jet diffuser in the ceiling. Already ducts have being install with a damper in each branch duct. But the sub contractor has cut the duct from bottom to connect the jet diffuser. My worry is that, is it OK if we take a flexible from bottom of branch duct & connect it to the jet diffuser & does a damper & plenum is require at each jet diffuser? I am worried about the Noise level....Please put your comments! Your suggestions are highly appreciated.

 

[Drazen]

you have to calculate ductwork and find out balancing pressure at each branch, than check whether calculated balancing pressure fits within range of balancing dampers.

noise at dampers usually takes place when throttled too much as a result of flaws in calculation which has to be "rectified" by fitters.

 

[tcihvacff1]

Thanx Drazen! I got it but some clarification pls..
Did you mean to check whether the balancing pressure calculated for each branch is coming within the range of VOLUME CONTROL DAMPERS installed at each branch?

 

[Drazen]

tcihvacff1,

i see you could absorb more knowledge on it, but it is not possible to provide the whole picture via tip.

in general, "simple" dampers that i assumed have design characteristic with pressure drop-volume relation. you nozzle also have characteristic which shows pressure drop at your design volume. firstly you should calculate ductwork with nozzle pressure drop, than determine how much balancing is needed on branches. than your branch damper should have exact volume and exact pressure drop, and that is not possible in practice. therefore, you need additional adjustment on nozzle. so you would actually have two dampers in series that will enable you to reach design volume in balanced state.

normally, i am trying to design ductwork, so that pressure imbalance on branches fits the range of nozzle's dampers, so additional branch dampers are needed only where larger imbalance is unavoidable. if your ductwork is designed that way, branch dampers can be used for volume control, but i rarely see that, branch dampers often means that designer did not bother with balancing by sizing at each branch, but specified dampers to take care of it.

after calculating, you should know what is true.

 

[willard3]

You should also come to grips with the fact that ductwork is seldom installed as you designed it unless you are doing the field coordination and are punctilious about correcting shop drawings from the contractor.

 

[317069]

it is ok, don't worry.

 

[tcihvacff1]

Ok!
Thanx to all for your valuable suggestions. Anyways I will proceed hoping for better results.

Drazen! Thanx a lot.