HVAC air pressure loss through a dryer vent hood

[guitarboyled]

Hi again guys

I'm trying to figure out the pressure loss through a dryer vent hood. Can't quite find anything in the ASHRAE loss coefficient tables. But I have an old version.

 

[guitarboyled]

Here are pictures

 

[berkshire]

I do not know quite what you are asking. Most dryer hoods have very little loss, as long as the back pressure flapper plate is free to swing.
The greater problem is lint build up. and line loss.

According to Frigidaire (most other makes are likely similar), dryer vent back pressure "MUST NOT exceed 0.75 inches of water column" as tested with an inclined manometer. If the vent system back pressure is less than 0.75 inches of water column, the vent system is acceptable. (Amanda recommends 0.60 inches of water column or less for some of their dryer models.) If a manometer reading is higher, the system is too restrictive and the installation is unacceptable.

Hope this helps, if not come back and re-define your question. As a general rule the actual loss of a louvre or vent hood can only be found by testing.
B.E.

 

[zekeman]

If the louvres exit area is much smaller than the duct area, the total loss is close the the exit velocity loss, or
V^2/2g
head in ft of air.
If your fan curves are given in inches of water then the conversion is
multiply the feet of head by .075*12/62 *530/(T+460)