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How does Make-Up air work in the winter?

11/16/22       
Matt Meadows

We're dealing with a lot more issues with drawing a negative air pressure in our building this fall/winter than previous years because we've added more spray booth and flatline sprayers. It's such that it's affecting the CFM of nearly everything.

Thankfully we're not above the Mason-Dixon so our winter temps aren't too bad, but we have many days that never leave the upper 30s, low 40's in the coldest months.

How can we effectively bring in a large amount of air into our building to accommodate all these machines and yet not have a frozen crew working the shop floor? Diesel and propane costs are outrageous right now.

We're considering installing more natural gas furnaces, but the issue we're running into is that the negative air pressure is already tripping off our current gas furnace because the furnace heat flue cannot draw enough air from the building to get a clean burn. The flue pipe has to exhaust out of the building for safety, which puts the whole burner right in the middle of the pressure differential. We'd have to install the furnace outside the building somehow to make that work and that's not an option unfortunately, structurally.

11/16/22       #2: How does Make-Up air work in the wi ...
shenendoah

Dedicated air make up systems which can or will supply air to booths/flatline systems year round - and heat when you need it. Contact your booth sales people. You can get real fancy - read expensive - or a more simple system that will at least allow you to have a positive air flow and also regulate heat intake as needed. Your booth people can identify exactly how much cfm of air intake you need.

11/16/22       #3: How does Make-Up air work in the wi ...
herb johnson

first question...do all the booths run at the same time
second question.....does that flat line machine run at the same time as they booths.

these are very important to start off with because if yes, you can really have a pretty simple system oh, one last one, any idea if you are soon ready to add additional booths.

now, some of the more difficult things to consider and a lot depends on a few things, your relationship with fire dept and their knowledge of codes, your insurance people, and the transfer eff. of your spray eqpt as this can be complex depending on your locality.

national codes are pretty much written so at the end it ends with "up to the person who has local jurisdiction", so who could that be in your locality, a single person or muitiple inputs???

then we can really muddy the water with lel of the spray booth area, , lower explosive limit" which equates to how many fpm per sq ft of frontal area do you need to prevent the "lel" of the atomosphere.

where i am going with these paragraphs is one of the simplest things you can do to save "valuable and expensive" heated plant is to add a vfd , a variable frequency drive to you spray booth. most not all because there is a lot of junk booths being mfg'd state and not really looking for argument at a range of between 100-125fpm exhaust. so if you ten wide x10 high booth,, height and width, working dimensions not overall, except in d/draft booth, would have exhaust air amounts do the math 10k-12.5k cfm.

so in a perfect world, you breeze thru, no hassles anywhere get a single speed unit and use the vfd's to balance the room.

your flatline machine will have the cfm on the drawings. total up the output, add ten percent safety factory and my guess in todays times 10-16 weeks a put an airmake up into next years budget unless you can find something used.

sorry, missed one point, the air make up works like a gas home heater on steriods wich was your headline question. to give an idea of how many btu cfm you need for ur plant,.......btu's = cfm x 1.08 x 70

70 is the temperature rise from zero but air makeups have thermostat's that typically work like a house jobby.

for budgetary purposes i would figure about 2.00 a cfm. if your scenario is more involved leave a note on here. at minimum get vfd's asap. a no brainer in your situation. fwiw.imho.,

good luck.....herb j

11/16/22       #4: How does Make-Up air work in the wi ...
herb johnson

forgot one thing, not being harsh, i assumed you know what a variable frequency drive is so a real brief primer........

it works like a rheostat knob/dimmer switch on a light fixture,

push a down arrow speed of fan slows, push an up arrow, speed goes up.......

if you have single phase, you need to double the size of the vfd, three phase no need

11/16/22       #5: How does Make-Up air work in the wi ...
Leo G Member

Sealed combustion chamber system with the intake an exhaust outside which makes the system isolated from the inside.

11/16/22       #6: How does Make-Up air work in the wi ...
RichC

Seems you need an engineer that understands industrial factory air flow. Does your dust collector vent outside too? That means you are back drafting in it too. Good chance you are back flowing sewer gas from your bathroom if that much back flow comes from the furnaces. Best guess is that your booth fans are grossly oversized.

11/17/22       #7: How does Make-Up air work in the wi ...
shenendoah

Hi Matt,
All have presented valuable insight and information. Maybe in warmer times ya'll keep the shop doors open so positive air flow is never an issue.
Well, with all your growth and upgrades ( congratulations! ) it has become an issue when all doors are closed during the cooler times no matter what your this and that configuration or whether or not there is operating equipment simultaneously competing for and starving for sufficient air supply.
If you ring up your booth/ spray systems supplier(s), they will, if not able to service/answer your questions, they will be able to direct you to a company that can answer/ solve your questions and issues.
Been there more than once. Good luck.

11/17/22       #8: How does Make-Up air work in the wi ...
herb johnson

actually if you can do math and have mechanical contractor hvac contractor, you can handle most everything yourself. it is all very basic math as outlined above. the more hands you involve the more the cost. just my two cents. especially if you tend to run most of your booths and flat lines at the same time. a simple single speed air make up unit with booth mounted vfd's is as simple as it gets......

12/19/22       #9: How does Make-Up air work in the wi ...
Scott

Some great information provided. There is only one way to supply a spray booth if you also require heat, that is a make up air unit. Like Herb mentioned you need to match your intake to all the cfm that your booth or booth’s or spray line are removing. These systems are not cheap. Generally they are also the only thing that will be approved by your insurance company and building/fire codes. If you are in a really hot climate you can just draw air from the exterior with a filter bank. You also need the right size of opening for that.
These systems need to be designed by a mechanical engineer. After they are installed they are balanced to create a perfect flow with no turbulence.


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