Recirculating Paint Both?

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PostPosted: Sun Dec 20, 2020 8:28 pm
I am in the early stage of thinking about building a paint both. Probably a semi down draft as a full down draft makes the concrete work more complicated. Probably 14x24x9.

But my biggest concern right now is heat, keeping the both warm. I am in northern Wisconsin and most of my painting will be done in the winter because that is when I have time, so below freezing outside. I hate the thought putting in a big enough furnace to heat incoming air.

This will be attached to my 56x88 shop that is heated to 65 degrees. But if I just stuck the air out of the shop it will cool it down. So I am wondering if anyone has ever had the exhaust from the both dump back into the shop so you are just recirculating the heated air of the shop. I am OK with some odor and fumes coming back into the shop but definitely don't want paint itself covering the shop. Also don't know if their are any flammability concerns. Do they make a good enough exhaust filter to get rid of everything?

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PostPosted: Mon Dec 21, 2020 12:24 am
So this is something I have researched a few times over the history of our furniture restoration company and just keep coming back to this..... you or I are neither scientists nor finishing chemists. With automotive coatings we especially have a rather dangerous component that in my opinion MUST leave the building....ISOCYANATES. Even though you may remove overspray and smells you just don't know if all those ISOS are gone. Add to that the fact that even when done spraying the car is still flashing them off for quite some time. I have seen both small portable collision station air recyclers and even large whole building spray booth recyclers. Most of these have at least 4 stages of filtration. The large building units still require at least 25% new air be added to the mix. I think the problem is that in a home made system you would need activated charcoal to grab the ISOS and would have no idea when that media became fully saturated. And.....flammability is another messy subject as well. If a system is efficient enough to catch enough emissions then you are literally storing flammable materials.
What we came up with to deal with this somewhat in furniture refinishing was to have our booth located in our finish room which has a sealed infra-red tube heater. In this way the objects are warm and stay warm even when the air is being exhausted. The fact that the unit is also warming the concrete slab also gives us faster recovery of air temps. as well.
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PostPosted: Mon Dec 21, 2020 1:53 am
Can you use a crossflow or counterflow HVAC heat exchanger for the incoming and outgoing air? Lose the isocyanates but keep most of the heat.



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PostPosted: Mon Dec 21, 2020 10:19 am
JBinMD wrote:Can you use a crossflow or counterflow HVAC heat exchanger for the incoming and outgoing air? Lose the isocyanates but keep most of the heat.


I had thought of that. Just not sure how big of unit it would take with the amount of air exchanges you need if it would be efficient or not. I have not started calculating the air needs yet.



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PostPosted: Tue Jan 12, 2021 1:06 am
Hi Mopar_Mudder,

Something that I just finished up with for my shop is a radiant heated floor. I used PEX tubing after insulating the footings and below the final slab, I then installed the PEX and poured a concrete floor for a radiant floor heating system. The tubing is real cheap on line for 100' rolls. I am all electric at my place, so I'm using a tankless hot water heater and a circulating pump to move the water. It is amazing how warm the shop is. :happy:

I suggest that you look into it, I assume you are building the booth from scratch since you say concrete work. I did the tubing and insulation a few years ago when I built the shop and I'm just getting to the heating this winter, boy is it worth the cost of doing it. Consider doing just the tubing if your on a budget, you won't regret it when you do get it all done.

Anyway, just another idea to consider in the cold North.

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PostPosted: Tue Jan 12, 2021 4:52 am
Mopar_Mudder wrote: I am wondering if anyone has ever had the exhaust from the both dump back into the shop so you are just recirculating the heated air of the shop.


This is even more dangerous than positive pressure booths - feeding a mix of air that is both flammable and highly poisonous back into your shop is maybe the silliest thing you could do.

Professional booths have at least 2 air circulation settings. Firstly exhaust where the nasties are sucked out the outlet and into a flue to go outside. This is the ONLY thing to do with these dangerous fumes. The second option is a recirculation mode where the air in the booth is sucked out the outlet but then fed back into the inlet, usually via a heater which is capable of getting the booth to around 60C. This is 'baking' and only needed for 20-30 minutes to harden the clear.

If you design your setup to do similar you'll lose warm air while you're actually painting, but that isn't long at all.

I'm still debating a home booth setup myself. I looked at the activated carbon but it can become saturated very quickly and isn't cheap. At the moment I'm leaning towards a water wash type arrangement which I'm pretty sure I can achieve with modified high capacity evaporative air coolers. They're quiet, they move lots of air (8000m3/hour) and not overly expensive(under $500AUD each), so 2 would do.
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PostPosted: Tue Jan 12, 2021 9:49 pm
Mrfixit_PDX wrote:Hi Mopar_Mudder,

Something that I just finished up with for my shop is a radiant heated floor. I used PEX tubing after insulating the footings and below the final slab, I then installed the PEX and poured a concrete floor for a radiant floor heating system. The tubing is real cheap on line for 100' rolls. I am all electric at my place, so I'm using a tankless hot water heater and a circulating pump to move the water. It is amazing how warm the shop is. :happy:

I suggest that you look into it, I assume you are building the booth from scratch since you say concrete work. I did the tubing and insulation a few years ago when I built the shop and I'm just getting to the heating this winter, boy is it worth the cost of doing it. Consider doing just the tubing if your on a budget, you won't regret it when you do get it all done.

Anyway, just another idea to consider in the cold North.

TX
Mr fixit_PDX
Chris :)


I already have in floor in my entire 56x88 shop and yes it is nice. Not really practical for a paint both as it can be slow to recover when all the heat is sucked out of the room in short order.

Right now my thought is exhaust to out side and run the make up air through a water to air exchanger as it comes in to heat it up. Water would be heated off my existing boiler. Not sure on the size of exchanger that would be needed though, might not be feasible with the CFM needed.



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PostPosted: Tue Jan 12, 2021 9:50 pm
NFT5 wrote:
Mopar_Mudder wrote: I am wondering if anyone has ever had the exhaust from the both dump back into the shop so you are just recirculating the heated air of the shop.


This is even more dangerous than positive pressure booths - feeding a mix of air that is both flammable and highly poisonous back into your shop is maybe the silliest thing you could do.

Professional booths have at least 2 air circulation settings. Firstly exhaust where the nasties are sucked out the outlet and into a flue to go outside. This is the ONLY thing to do with these dangerous fumes. The second option is a recirculation mode where the air in the booth is sucked out the outlet but then fed back into the inlet, usually via a heater which is capable of getting the booth to around 60C. This is 'baking' and only needed for 20-30 minutes to harden the clear.

If you design your setup to do similar you'll lose warm air while you're actually painting, but that isn't long at all.

I'm still debating a home booth setup myself. I looked at the activated carbon but it can become saturated very quickly and isn't cheap. At the moment I'm leaning towards a water wash type arrangement which I'm pretty sure I can achieve with modified high capacity evaporative air coolers. They're quiet, they move lots of air (8000m3/hour) and not overly expensive(under $500AUD each), so 2 would do.


I figured it was going to be a bad or really expensive idea, just wanted to through it out and see what people are doing in cold climates for make up air.



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PostPosted: Thu Jan 14, 2021 11:16 am
Forced air heating would be the best option in my opinion.
You could supplement your heat with Natural gas furnace if its available ? or Propane yes Propane is more expensive but you'd only be using it when needed to supplement when running a Paint booth.

Recycling the heat into a heat ex changer while it may sound like a great Idea just wouldn't be very efficient my opinion Not enough heat energy to make a great deal of difference and it would be expensive as well.

Its a Physics thing, The available energy in room air and the amount of energy or work it takes to raise 1 gal of water 1 degree in a certain amount of time.
Or the Amount of energy or work it would take to raise the outside air 1 degree in a Air to air heat ex-changer. It takes a certain amount of energy to do either.
Add to it the efficiency's of or lack of efficiency of the heat ex changers being used.


You could use a Huge Carbon filter and just filter and recycle all your exhaust back into the shop but how long it would last ? and how effective it would be at removing Isocyanates and How expensive it would be to purchase and replace? It would be totally cost prohibitive in my opinion.
Especially in light of current governmental restrictions on Painting now and current plans by OSHA and others, It would not surprise me at all that the sale of and application of all automotive finishes be done by Licensed professionals only in the next few years.

Just like Guns They cant get a restriction on Guns sales so they restrict Ammunition sales. They will do same for Painting by restricting the sale of paint to Licensed shops and painters who have already been inspected to have certain equipment and BS Training.
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PostPosted: Thu Jan 14, 2021 1:07 pm
Doright wrote:Recycling the heat into a heat ex changer while it may sound like a great Idea just wouldn't be very efficient my opinion Not enough heat energy to make a great deal of difference and it would be expensive as well.

Its a Physics thing, The available energy in room air and the amount of energy or work it takes to raise 1 gal of water 1 degree in a certain amount of time.
Or the Amount of energy or work it would take to raise the outside air 1 degree in a Air to air heat ex-changer. It takes a certain amount of energy to do either.
Add to it the efficiency's of or lack of efficiency of the heat ex changers being used.


To be clear I was not talking about a air to air exchanger but a water to air exchanger, basically a car radiator. Run water from my boiler through the radiator at say 140 degrees to warm the incoming air.
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