Calculation of converging bullhead tee

[KZ001]

Hi,

How do I calculate the pressure loss of a converging bullhead tee in a return duct system. The tee has dimensions 23"x23" for the main duct and the branch. Thank you!

 

[Drazen]

..by finding fitting loss in ASHRAE Duct Fitting Database

 

[KZ001]

The pressure loss for a converging bullhead tee is not listed in the SMACNA "HVAC Systems Duct Design" or the ASHRAE Fundamentals.

 

[RossABQ]

Could be because it's a bad practice?

 

[SAK9]

If it has already been installed,measure it.If not do not do it!

 

[kacarrol]

I had someone ask the same question around the office here the other day. This is the best I could find:

https://www.google.ca/url?sa=t&rct=...d=3&cad=rja&uact=8&ved=0CDEQFjAC&url=https://

http://www.captiveaire.com/MANUALS/...yZMnp4_Q88tIzUw_IJpaA2w&bvm=bv.71778758,d.cGU

But I have no idea where they are citing those tables from.

For our system (it was designed by an inexperienced engineer) we will be changing the layout. But I thought I'd provide the reference anyway.

 

[Drazen]

calculation is based on those tables, and if you cannot find anything that resembles your case, you are outside usual calculation procedures.

you can either order cfd analysis from some faculty that would possibly cost as much as your total investment cost. the other way is, as sak said, to measure it if it's already installed.

there are ways to make guesstimate, but it remains guesstimate. you can sum loss of "normal" tee and reduction, and double it to take into account additional swirling caused by many direction change.

 

[Wilbur55]

Not a standard term, AFAIK, but it is descriptive: "trainwreck tee."
Illustrated and discouraged in the second post here for a water system:

http://www.poolforum.com/pf2/showthread.php/14444-Pump-Problems

 

[KZ001]

Thank you everyone! kacarrol, I have the same document but the source is unknown and I am not sure if I reliable. Thanks again!