Positive Pressure Spray Booth/Room Design question

I am dabbling with "positive pressure" paint room/spray booth.

I am only spraying Waterborne products.

My room is 16x20x 8 it is connected to another part of shop that is heated/air conditioned which is where i would draw the intake air from ...

If I set intake fans (couple of 20 inch box fans with filters ) near the ceiling, and a couple on the other end as exhaust fans near the floor would this be proper placement of the exhaust fans or do i want them at the middle of the wall for exhaust? Other suggestions also welcome.

Attachment 411226

Creative plan that includes a number of good design elements. So-called push-pull systems do help to readily remove contaminants. With the exhaust at ground level (best location in my opinion), no support is needed for the cardboard duct. You may find a need to supplement internal lighting in which case you will need an access port for electrical lines. Longer walls may need additional vertical supports. Of course, ensure the booth doorway is large enough for all your projects.

It would work best when you spray toward the exhaust port. The size makes me think that you would like to get to all surfaces, though. Does it need to be that large? A turntable would be useful to ensure you can always spray downstream.

The best set up will ensure laminar flow, i.e. in one direction from the inlet toward the outlet. I am concerned that the volume of air through the fan set up will cause turbulence which will impede your spray application. Multiple speed box fans would allow flexibility with the total volume. You can use tissue paper attached to surfaces with tape to check the final results. If they flap a lot, you are getting turbulence. You may find that a single fan at low speeds gives the best results.

Higher efficiency filters on the exhaust port may clog fairly quickly which will reduce air volume over time. Less efficient filters, of course, will cause increased build up on your fan blades.

Good luck and keep us posted on your progress.

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Originally Posted by David Utterback

The size makes me think that you would like to get to all surfaces, though. Does it need to be that large? A turntable would be useful to ensure you can always spray downstream.

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David-Thanks for the kind response...First the image I attached was for reference only. This is a "work in progress" project for me... I did a quick mock up with a couple of box fans on the exhaust side so you could get an idea...basically i roll a shelf with the fans on it in front of the door that leads to the outside and close the sliding door against it. Based on your response to me, should i basically do the same on the intake, with the exception of having the fans mounted as high to the ceiling as possible?

The " booth doesn't need to be 16x20 I can certainly pull a tarp down the length of the room and cut off a few feet. I do plan on making a turn table. I am thinking the largest thing i would paint in there would be a dresser.

I am attaching some pics to help make things clearer.

Attachment 411305

^^^This is the intake side. This room is heated, AC etc. My thinking would be to put the box fans on a rolling shelf ( as high as i can )and fit between the doors

Attachment 411306

^^^^^ This is the Door that leads to outside


Attachment 411307

^^^^ Door leading outside with fans on shelf in doorway

Will your booth be built inside the room you show or be the room itself? Will it be used frequently or only as needed? Exhausting conditioned air can be expensive and put demands on your hvac system beyond its capacity. The dimensions and flow rate make me think the room volume may be exchanged in a short time which means the booth quickly would contain mostly outside air.

A further thought - premium filtration of the inlet air would reduce the need for higher efficiency of the exhaust air filtration.

Quote:

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Originally Posted by David Utterback

Will your booth be built inside the room you show or be the room itself? Will it be used frequently or only as needed? Exhausting conditioned air can be expensive and put demands on your hvac system beyond its capacity. The dimensions and flow rate make me think the room volume may be exchanged in a short time which means the booth quickly would contain mostly outside air.

A further thought - premium filtration of the inlet air would reduce the need for higher efficiency of the exhaust air filtration.

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It will be the room itself. Used only as needed. Please clarify "premium filtration"? Is this simply a furnace filter with a higher MERV rating?

Should i use two intake fans since i have two exhaust fans? I also have some old furnace blower motors avail. I do like the box fan fans concept as they are lighter and quieter :-)

"Premium" does not refer to anything in particular. Your own search should lead you to the proper filtration to limit the particulate penetration you have in mind.

Box fans are inexpensive and the typical 3-speed will permit experimentation. You will need a little higher input volume than exhaust if you wish to achieve positive pressure. I do not know that this is necessary but would help limit infiltration through cracks. However, higher efficiency filtration on the inlet than the exhaust would likely mean that you would have lower input than output which would reduce pressure inside the room, all other factors being equal. You could adjust tis with small baffles on the exhaust.

The set up you show does not show the ground level exhaust. I doubt this is a problem since there does not appear to be much risk for entrainment of exhaust air.

Hope this helps.