Turning my garage into a booth

rustover

rustover

Member
Hello guys. Great forum here. My name is Russ and I have two camaro projects that I'm hoping to be able to start working on again soon. I had an addition built onto the garage and I'm wanting to learn to how do body work and paint. I want to be able to do most of the work on my two projects.

This addition was suppose to be dedicated for this type of work. I have almost got it too nice to spray paint inside of it for different reasons, but I'm not going to let it stop me (I hope). The main size of the garage is 20x24 with scissor trusses. The ceiling height is around 12.5ft.

Let me know what you guys think about this: My plan is to pull fresh air from my existing garage into the new garage via an exhaust fan that is installed in the wall. I'm planning on installing two windows in the old garage that I can put filters in. The air would then pass through a filtered wall and into the spraying area, exiting through exhaust filters before the exhaust fan. The fan is a variable speed. I'm also planning on building doors to cover the filters when they are not in use.

The filtered wall will have a total of 15 tacky 20x20 filters:

3 filters on one side of the man door and 12 on the other side which will be directly across from the exhaust fan.

Here are some pics:

filterjpge.jpg


filters1jpg.jpg


filtersjpg.jpg


This is the other side (spraying area). I haven't cut the osb yet where the filters are:

3 filters area between the two white hanging towels:

filter2jpg.jpg


other side where 12 filters will be:

filters3jpg.jpg


Fan

exhaustfanjpg.jpg


exhaustfan1jpg.jpg


Here is the outside of the building:

buildingsidejpg.jpg


The fan has the automatic shutters that open when its operating.

I'm planning on putting plexiglass doors on both sides of the fan control, that way I can cut the fan off when entering/exiting the man door to keep the trash out.

Also this is a weird building. Its built on an angle to flow with my driveway and land layout. I'm thinking about installing a body shop curtain on the beam to isolate the rest of the front of the building.

beamjpg.jpg


Well that's what Ive been working on. Am I crazy, or way off. I have no idea on calculating air movement.

I have not purchased any lights yet. I know I want lights on the wall, just not sure which ones.

Thanks for any advice. Russ
 
How many cfm's is that fan? I had a setup like your doing years ago in my 24 by 24 garage. I just had the fan in one wall and no intake filters. I had a large pet door in the outside entry door. All I would do is turn the fan on and open the pet door flap and paint. Some of my cleanest jobs came out of that setup. Your setup with the intakes should be plenty of intake air. I think I remember my fan being around 3700 cfm's and I can tell you that it didn't move much air. I think that is why it came out so clean. You would have to spray your coat and get out of there.
 
20 x 24 x 12.5 = 6000 cubic feet of air.
In order to change out the air 2 times a minute you will need a 12,000 CFM fan. Your filters will have a "flow rate" which tells you how many CFM per minute they can handle so be sure to include enough filters to handle your total CFM of air flow.
The standard velocity of air in a commercial booth is 100 feet per minute for cross flow and 50 feet per minute for down flow booths.
Most homemade booths are based off the exchange rate rather than feet per minute air velocity since the cost of proper sized fans is very high. My booth has an exchange rate of once per minute and it is not really moving much air. I think the goal is somewhere close to 3 times a minute.
Also having a larger filter bank (intake and exhaust side) will move the air in a large mass from one end to the other and decrease the amount of turbulence and back drafts.
Be sure to put good lighting above and on the sides of the booth. Poor lighting is a real pain when spraying.
 
[QUOTE='68 Coronet R/T;15534]20 x 24 x 12.5 = 6000 cubic feet of air.
In order to change out the air 2 times a minute you will need a 12,000 CFM fan. Your filters will have a "flow rate" which tells you how many CFM per minute they can handle so be sure to include enough filters to handle your total CFM of air flow.
The standard velocity of air in a commercial booth is 100 feet per minute for cross flow and 50 feet per minute for down flow booths.
Most homemade booths are based off the exchange rate rather than feet per minute air velocity since the cost of proper sized fans is very high. My booth has an exchange rate of once per minute and it is not really moving much air. I think the goal is somewhere close to 3 times a minute.
Also having a larger filter bank (intake and exhaust side) will move the air in a large mass from one end to the other and decrease the amount of turbulence and back drafts.
Be sure to put good lighting above and on the sides of the booth. Poor lighting is a real pain when spraying.[/QUOTE]

To help clarify what 100 fpm means. You take the height x width x 100. That equals the number of cfm to move the volume of air in your "booth" 100 feet in 1 minute. 24 x 12.5 x 100 = 30,000 cfm.

My "booth" is 18 x 24 x 10. My 2500 cfm fan is not adequate. 18000 is the magic number for mine, I need lots more air flow .
 
In my experience with the two booths I've made and adjusted over the years is that the slower the air movement the cleaner the job. My fan is a 24" tubeaxial with a 3hp motor and variable freq drive to adjust the speed. Intake filter area is 12 24" by 24" tacky filters. The slower the fan the cleaner the clear. I think my fan wide open moves around 8500-9000 cfm. Most old booths use the old 24" tubeaxial. In my research now it shows most all use a 32" tubeaxial running 12,000+cfm's. I think it has more to do with removing the clear fog for the safety of the operator more than those large cfm's doing a cleaner job.
One problem in my opinion with those large fans lies in the winter. They move so much air that you deplete your building spraying the car and cold air is running over the vehicle. Mine fan will wipeout my shop heat in a minute since I have to open the entry door in order to spray as the fresh air comes from somewhere. I've addressed this issue and it's no longer a problem but not all shops have hot water heat to heat the outside air with a radiator. It's was in the lower 20's yesterday and that type of cold air will wipe your building out and by the time your done with your coat it's cold. I've never had problems that I know of from this but it probably isn't that good to start spraying in 70 degree air and finish in the 50's or less. Usually less if it's an overall. If I clear a hood in my booth it will remove all of the cloud in probably 25 seconds.
 
Thanks for the replies guys. The best I can tell the fan is a 1210-3930 cfm. Its a variable speed fan with an rpm from 500-1650. I emailed the vendor that I purchased the filters from asked about the flow rate. This was their response: TEST AIR FLOW 1,200 CFM, INITIAL RESISTANCE .21" wg (water), FINAL RESISTANCE 1.00" wg. looks like a drop of about .80" wg .FYI Avg Dust Holding Capacity is 183 grams.

Looks like I need a way larger fan.
 
That's usually the case. The large fans are so expensive that us home shop guys usually shoot for a decent compromise. If you can get the air exchange rate to a satisfactory level (like Brad is using) it will save you some money.
Brad, what size is your booth and what would you say your air exchange rate is when running your fan at reduced speed like you do?
 
I have a 24" fan in the back wall of my garage. it pulls more fresh air than I can supply. I turn it on low when I clear. Ya there is a cloud but the job def comes out cleaner.
 
My booth is roughly 14' wide by 24' long by 9' tall with the cathedral ceilings. Basically copied the basic size of standard commercial booth since that is the size of the fan I had. I also roughly copied the intake filter area and exhaust area. I have no idea on the exchange rate. Seems to turn over air pretty good. My old 24' by 24' with the 3700cfm would take minutes to clear the fog where my setup takes less than half a minute. One thing I have learned through trial and error is you can't have to much intake filter area. The more filter area the less the wind tunnel (turbulance) to pick up the crap. That is why the slower speeds slow down the air flow and less crap is kicked up. If I open the front door or would put more filters in the front then I can run the booth wide open with less turbulance. I can stand there and feel the difference. I've done so much hands on research that my cleanest jobs come from lots of intake area with just enough fan to exhaust the fumes at a reasonable rate.
My booth is designed at a semi downdraft with air coming in the front ceiling. The way it is I'm about maxed out for my intake square footage. If I could I would have intakes filters on every square inch of area. (replacing filters often makes a huge number of filters not very cost effective.)
I think the current crop of booths are designed to protect a painter for 8 hours shifts with a lot of air turnover. I think the guy in the garage painting one car a year can get by without that air flow. Just use the right protection equipment, spray, and get out.

Use your fan and see what happens. When I worked in R&D for mechanical parts all the calculations and computer modeling in the world didn't dial the product in right away. My job was to test the parts being designed and I can tell you that you never know what the real world deals you. That is why I don't pay much attention to calculations and such. Sounds ignorant but you learn more with trial and error.
 
That last sentence just sounds awful. Not sure what I wanted to say but not that. I guess use the industry standards as a guideline and go from there. If there was a configuration that worked better and cheaper then they would have already found it.
I think your arrangement will work very well for cleanliness, just not sure how much air turnover until you run it.
I think those lights will work nice. Have you talked with an insurance agent? They might make you use the legit booth lights?

After all my dinking around I wish I would have gone into this thinking the fan's only job is to exhaust fumes. Not produce a clean paint environment. I just never sprayed in a real booth before and I miss understood how it all works. If I could spray without the fan on I would, but I'm not going to put myself into that environment though.
 
Brad, I understood exactly what you meant. I know I personally always over think things. Its just in my nature. I have thought about my garage setup hundreds of times and in the end I always have to remind myself. I am painting in a garage!! I am not in a booth. Stuff is going to get into the paint and I can supply 7000cfm of fresh air to accomodate what my fan can pull. In the winter its even harder. I have a nice heater setup so that usually isnt an issue but still.

Its kind of funny, but the cleanest job I have ever produced in my garage was when it wasnt even set up as a paint booth! I have the door open with 2 box fans and stuff everywhere.
 
Too much air flow is actually bad for a paint job! You want just enough flow to be able to see but not enough to steal away your paint flow. Die-back and others problems are just some of the problems from too much cfm.
 
Sooooo, what is the general consensus on exchange rate? 1 per minute, 1.5 times per minute, once every two minutes?
Personally I think larger filter banks greatly reduce turbulence in the booth by moving a greater mass of air from one end to the other. This would also reduce the velocity of the air while still accommodating a decent exchange rate.
I really would like more thoughts on this since I am planning to redo my booth in the near future.
 
A large filter area slows down the speed of the air entering the booth and makes for less chance that particles will be moved in the airstream-less dirt. Some of the best booths will have diffuser panels in a plenum to evenly distribute the air across a large filter area.
 
Everytime I added more intake filter area the air flow was smoother and paint was cleaner. Didn't matter what the fan speed was either. One of my early brain farts was to lay wire grate in the ceiling plenum and use the blanket style intakes. It took me a couple years but that grate that the blankets laid on was very restrictive and turbulant. Even though I had a large calculated 8' by 8' intake area the mesh in the ceiling was killing me.

A local guy that made his own booth swears his jobs weren't very clean until he could crack open the man door and have it stay there instead of slamming shut. He kept adding intake area until his door idled open. This only makes sense.
 
So for someone building a temporary booth that is between 1200-1500 cubic feet is there a fan or maybe fans that have enough CFM to pull 2 times a minute or 3000 cfm but can also run off of 120v? I looked at Home Depot and none of the 120v fans have any type of CFM rating.
 
20" box fans move about 2500cfm If there are no flow restrictions.

http://www.homedepot.com/p/Lasko-20-in-3-Speed-Box-Fan-3733/100405665

What are the dimensions of your booth? Why I ask is the rule of thumb for a cross flow booth is 100 x sq feet of end wall = cfm
Don't kid yourself that a couple box fans will flow 3-5k of air in this application. To move that much air it takes horsepower, like 5 or more.

I too have painted in my home made garage/spray booth with box fans and also with louvered wall fans.
Best results were with 2- 1/2hp 16" wall fans mounted in a vertical stacked position in the middle of a man door opening.
I mounted them on a piece of cdx and mounted it to the door jam as you would a storm door.
On the opposite end of the garage I had 1 filter, 7'x16' x10 micron.
It was nothing more than Hoffman filter paper stapled to the door jamb of the garage door. None of my other attempts were nearly as good. Hoping my current attempt will work great but it isn't finished yet.
I really think the area of the filters cannot be to big, no matter how big.
My current attempt is going to have 160ft2 of intake filter and 80 ft2 of exhaust filter.

My one concern using non approved items is the switches. They are the most likely arc source. My personal process is to turn fans on before any spraying, and when finished spraying I unplug them - where the extension cord is plugged into an outlet outside of the "booth". I do not switch lights on or off either. Once on they are on until the booth is totally clear of fumes
 
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