Pressure Loss Coefficient - Tee 1

[bautec]

I have looked into the minor loss coefficient of ASHRAE booklet (miss pages), unfortunately I couldn't find anything on an open chamber pressure loss (see attached drawing).

Only one fan would operate at one time and the flow will diverge into two. I understand that to analyze the pressure losses in the two bends and in the chamber, you cannot treat them as only 2 elbows because the flow isn't directed and split into two streams smoothly by ducts.

Anyone has any idea to approach this pressure loss analysis?

 

[HVACBoston]

I think the area downstream of the fans might be classified as a plenum. If there's no real directional flow, but only pressure, then use the unducted performance of the fan. ASHRAE pyramidal diffuser with a wall could be used, with high L/D.
Then the ducts are treated as a Plenum to rectangular contraction (ASHRAE SR1-1)
Anything else means you are trying to model a bullhead tee, which isn't good news.

 

[bautec]

Thanks HVACBoston
I agree with you that the open chamber shall be treated as a plenum and SR1-1 coefficient can be used for the loss from the chamber to the narrow passages.

But I can't find anything on duct---> plenum in my ASHRAE copy. Would ER4-1 be a close one?

Can it be treated as a sudden enlargement? I suspect not because the flow would not be in one direction when it enters the chamber and become turbulent.

http://www.pressure-drop.com/Online-Calculator/pda/0301.html