Exhaust fan / duct question - DIY Chatroom

vit · 10-19-2009, 01:08 AM

Hi!
I'm building a spraybooth with an exhaust fan for airbrushing.
I've got a booth made with exhaust at the back wall, with air plenum behind and a squirrel cage fan.
I have 2 setups in mind:
1) With a fan attached to the back of the booth/plenum and duct out of the window.
2) With fan mounted on the window with duct between booth/plenum and a fan.

The duct is a 3" diameter flexible duct. Exhaust opening on a fan is 1 1/4" X 2 1/8".
In which setup will I have more fan sucktion power loss?
Setup 2 is much easier for me to make at home...
Any help will be great! Thanks!

fireguy · 10-19-2009, 02:38 AM

Is the sprayed material flammable? Is this commercial usage?
Is the sprayed material going through the motor? Is the motor listed for flammable use? Make up air? What is the CFM of make-up and exhaust air? Is this a listed booth?

vit · 10-19-2009, 12:22 PM

Is the sprayed material flammable? No

Is this commercial usage? No

Is the sprayed material going through the motor? No

Is the motor listed for flammable use? No
Make up air? ????
What is the CFM of make-up and exhaust air? No idea, the fan has no listing on it.

Is this a listed booth? No

So which setup do you think is better?

fireguy · 10-19-2009, 01:22 PM

Quote:

Originally Posted by vit

So which setup do you think is better?

Normally, the systems I work on are designed by an engineer, and we are given both exhaust and intake air requirements, duct sizes, and fan part numbers. And even then, we find problems in moving air.

You can purchase an annemomoter (sp?) which will measure air flow. Mine was less than $200.00 Or you can call a HVAC contractor to measure the air flow. One reason for intake air is to prevent expensive heated or cooled air from being blown outside. The air flow going out shoud be about 80 to 90 % of that brought in for intake air. I am going to assume this is a hobby type of booth, open face. The fan mounted on the wall will be the easiest to install. Is the exhaust duct a ridgid duct and not something like dryer duct? Dryer duct might collapse when the fan is on. And I am supposed to tell you to contact your local building department before any modifications are done.

Yoyizit · 10-19-2009, 05:51 PM

Quote:

Originally Posted by vit

1) With a fan attached to the back of the booth/plenum and duct out of the window.
2) With fan mounted on the window with duct between booth/plenum and a fan.
The duct is a 3" diameter flexible duct. Exhaust opening on a fan is 1 1/4" X 2 1/8".
In which setup will I have more fan sucktion power loss?
Setup 2 is much easier for me to make at home...
Any help will be great! Thanks!

I think #1 will work better because the area of intake is supposed to be 4x the swept area of the blades, but this library book
http://www.amazon.com/Mechanical-Eng...5985475&sr=8-4
is more credible than I am.