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Spray Booth Intake Size6/30
I am trying to find a calculation or whatever other method is used to figure out how to size the intake openings for a booth.
I have a Colmet 12 x 8 booth running a 30" 12,000 cfm fan on a VFD. We just had a room built around it that measures 12 x 15 x 13 feet not including the actual booth dimension. The booth itself to the filter wall is 12 x 7 x 8. So we are looking at 3,012 cubic feet within the room all together.
I'm trying to figure out how large of an opening I need for intake air that will give me 100fpm flow. At the same time, I'm trying to figure out the best placement of the filters on the back wall across from the spray filters. The booth is 8 feet tall and my cross facing wall (from the booth) is 13 feet tall.
I was planning to put the intake filters higher up so that I create a dead space on the back wall for drying. And to also pull cleaner air through the intake filters. My concern with this is that all of the air is going to be exhausted through the top of the spray booth filters and not down lower (mid level to floor level) where I will be spraying parts.
Or is it better to space the filters out over the entire back wall with multiple individual openings for a more even cross flow? (I started reading about turbulent air and all that which has me thinking to much and confusing myself now).
The obvious problem with having intake filters placed say 2 - 6' off the floor would be that I have no dead space to put freshly sprayed parts. They would also be right in front of intake filters (that don't stop everything from coming through) and I would get debris all over my finish.
I'll post photos of the room soon.
where does the intake air come from?
I'm in NY right next to NJ. So yes, it will get cold in the winter.
The intake wall is situated right next to an 8 foot bay door. The thinking was that we would intake clean air right from that door rather than pull intake air across the entire wood/metal shop before it enters the booth.
We did look into a makeup air unit. We are 5 months into business and quite frankly dropping $25,000 on a unit and installation isn't in the cards. I wish.
I'm in NY too.
It's going to suck for sure when winter is here. The shops I worked in before starting my own business worked in the same manner. Basically, you crank your heat up and heat the shop and spray as much as you can before that temperature drops to 50. Then you have to stop and reheat the shop and continue. It's a total pain in the ass and slows you down, but we always managed to get it done. I'm just going to have to get it done. We have multiple heaters throughout the shop so it heats up the whole 3500sq ft shop fairly quickly (about 10 to 15 minutes) from 50degrees to 65. The fan is also on a VFD so in the winter time I'm planning to slow it down while I spray to try and gain as much spray time as possible.
We built the room to the size we did because it is also going to be a drying room, scuffing room, mixing room. I wanted to keep freshly sprayed parts away from any dust that is in the air (as much as possible). Sometimes the cabinetry boxes and panels are big or if we are doing a table or finishing trim lengths.
Perfect examples: I'm building a 13 ft one piece table right now that will need to be finished and kept in a dust free area until it's dust dry. The next job after that is going to be finishing 5,800 sour patch kids candy displays. We need to be able to load 30 or so of these things into the room in rows and just crank through them. I wanted to be able to contain the mess and again, keep saw dust and metal dust away from them.
Alright, I made some calls and was given the answer.
I need to have at least the same area for inlet air as I have for the exhaust so that I don't have too much negative pressure. And also so I don't put extra wear on the fan. maybe a slight amount of negative pressure.
As far as orientation on the back wall I'm still thinking it over. I can either put a big panel up there similar to how the booth filter bank is set up. Or I was thinking what if I space them out and spread them around? I realize this would create dead zones between each inlet, but won't all of the air streams just flow together anyway once they get closer to the exhaust wall?
I guess my thinking is that way I will have a spread of filters starting from near the ceiling and working down to about 6' from the floor. This would give me my dead space for freshly coated parts sitting 3 feet below that. And I'm hoping the air flow would be spread out better by the time it reaches the exhaust wall rather than it taking the path of least resistance if I just put all the filters in a big bank up top. I'm imagining there would be more air moving at the top of the spray booth than the bottom if I did it that way.
I've built both sanding rooms (for surfboards) and spray rooms. You need "more" air available than just a 30" intake that would match your exhaust. That'll be a disaster. Your door/jamb opening looks to be 6-7ft wide x 8ft high. So roughly 50sqft. I'd put a well sealed sliding door with at least 25sqft (more the merrier) of easily replaceable filters so you get a nice clean gentle draw. What you're describing now will lead to lots of swirling air. The less restriction on available air the better.
I was planning to put the filter bank in the back wall directly across from the booth face. Not in the doors. I wasn't trying to say the inlet will be the same size as the fan (30"). I was meaning to say my inlet is going to at the least, match the full filter bank square footage. On my booth that is about 70 sq ft. The full filter face is 7 x 10 (I think, or close to it).
The door opening is 8' x 8' that I am framing out with 2" angle iron that will have a heavy gasket applied to it. One door will have an overlapping piece of 3" steel with a gasket that overlays onto the other door to seal off the center seam.
Does that sound okay?
Well you actually only have 2340cuft total using your dimensions. Which will empty out in about 5seconds. If you enclose the booth from the top and sides of the booth to the walls you'll evacuate the air even faster. That's a lot of turbulence. I hope your fan is variable speed. Otherwise I would make your filtered intake area as big as possible. Your whole back wall should be open/filtered in addition to the door. I personally like explosion proof variable speed belt driven fans. #1 they're way quieter and can move plenty of air.
cheers and good luck
the more intake filters you have the less the velocity goiung thru each one
i like to have about fifty percent more intake air filters than exhaust, the filters are cheap, maybe 2 buck a throw, just my two cents
Thank you Bart and Herb,
I was going to start at 10% more area than my exhaust to get a feel of how fast the air was moving in the room. If it was too turbulent then I'll open up more wall and put in more inlets.
I am buying the filter material from a company called Chemco Mfg. Has anyone tried their AFR-1 or their Diffusion media filters? The AFR-1 stops particles down to 10 microns and the diffusion media stops particles down to 5 microns and has an adhesive to keep particles from letting loose. Having never used either one and I'm sure there is a decent cost difference, I'm wondering if I'm even going to notice the reward in the finish.