Static Loss in AHU Downturn Discharge Plenum

[BronYrAur]

I'm trying to estimate the static loss in an air handler discharge downturn plenum. I have a 54,000 CFM air handling unit. Air discharges from the supply fans, goes through a sound trap segment and then into a downturn discharge plenum. The plenum dimensions are 222" long x 31" wide x 89" tall. My duct opening at the bottom of the plunum is 206" x 21". There are no turning veins.

I am trying to determine static loss in order to see if adding turning veins is worth while. Any ideas on how to do the calcualtion?

 

[AbbyNormal]

Would usually be counted as part of the internal loss of a packaged unit.

On a blow through furnace type of unit, I used to allow about 0.1" for the downturn plenum.

You may also be experiencing a 'non ducted loss', used to allow outlet velocity times 1.25 for forward curved wheels, and velocity head times 0.65 for the BAF wheels.

Download tranes info on MCC air handlers, they usually publish their data based on a straight run of three wheel diameters before any turns on discharge. They show how to correct for the turbulence on a turn on the fan discharge as well. Get a good half inch extra to allow for with a turn on discharge sometimes, especially when the air is over 2000 FPM coming out of the discharge.

Sometime little plug fans are nice.

Take the "V" out of HVAC and you are left with a HAC(k) job.

 

[AbbyNormal]

"used to allow outlet velocity HEAD times 1.25 for forward curved, outlet velocity head times 0.65 for airfoil"

Take the "V" out of HVAC and you are left with a HAC(k) job.

 

[atlas06]

I'd throw in an additional 0.5" for bad workmanship. Consider some serious leakage as well, have a good ductwork spec and please don't allow duct tape!!