Make up air heater for spray booth

Greg_40

Thanks for the replies. My apologies for not offering enough information.

This spray booth is 10' x 10' x 8' in height. Airflow through it needs to be approximately +/- 4,000 cfm. Spray application is done mechanically through a computerized spray system, so no personnel are inside the booth during applications. The wood products travel on a moving belt with about 30-35 seconds cycle time from entering the booth to leaving it. At the entry and exit of the belt are openings in the booth approximately 4' wide by 10" in height.

I like the idea of recycling the air. They have filters in line currently to capture particles before the air leaves the building. By the way, whatever products are inside the airflow and inside the booth need to be of explosion-proof rating. This limits options.

Greg_40

Can someone on the Wall help me with this customer's needs? We have a customer with a small furniture manufacturing business. In their new spray finish booth, they need to maintain 6o°F air for the laquer & varnish finishes to set properly. Wood products are fed into the booth via moving belt and remain in the spray booth for up to 35 seconds per belt travel time.

We used Wrightsoft to determine that a 246,000 Btu heat output is needed. They do not have gas or oil for a fuel source, but electricity. They are considering a wood fired boiler to utilize their smallest scrap pieces that cannot be used elsewhere in the manufacturing processes. What I am needing is a heat exchanger (radiator of sorts) to give us this Btu output. Then, I will need to know the efficiency of transfer so we can size an appropriate boiler or series of boilers. Design temp is typically 5°, but lows of 0° are not unusual. That said, the air is currently drawn through an adjacent conditioned shop area. They are considering using outside air, through filters to keep a dust-free environment and not tax the heat source of the adjacent room(s).

Any suggestions where to start looking? Thanks!

Mike T., Swampeast MO

How large is this spray booth for a "small" furniture manufacturing business? 246,000 btu/hr is a LOT of heat. Did you compute based on 100% fresh makeup air?

Are people doing the spraying as the pieces pass by on the moving belt or is it automated?

jp_2

recycle air

why can't you filter and recycle air? change the filters daily? or an air to air heat excharger? air scrubber?

seems 246,000 btus per hour is going to cost more than the furniture?

Brad White

What is

the airflow rate and outside air design temperature?

Cost and type of energy is one thing. Harnessing it and controlling it is another.

If you can get that information to me I have something to work with, just to double check if nothing else.

Another thought to mitigate energy use is, can you draw make-up (excess ventilation) air from other parts of the building? Air that has already been heated. An appreciable percentage of this will mitigate the load greatly and not have the same temperature swings as when heating it up from outdoor conditions. Ed is right, an air to air heat exchanger (not at this process due to spray mist but elsewhere) might be essential.

Brad

EBEBRATT-Ed

If they are exhausting air as they must be then you are bringing outside air weather they know it or not. I would suggest an air-air heat exchanger to use for exhaust and intake-then heat the airstream with a hw coil.

ED

Greg_40

The operating time will vary from 1 to 3 hours per day at varying intervals. Fuel readily available is electricity at approx. $0.06/Kwh and wood scraps for a future wood-fired boiler. An air exchanger idea has been basically scrapped as adequate filtration is a problem. One cannot permit a heat exchanger to become coated with spray products- it would be damaged at worst case and lose efficiency at best.

Brad White_9

The non-use of a HEX

in the spray-mist environment is understood, Greg, we both agree. That is not what I was suggesting, but did suggest taking air from other parts of the building, excess air elsewhere in the plant, if any.

As one example, by code here in MA, we can take 50% of a kitchen's make-up air requirement from the dining area which keeps the energy costs low. Also this air originally supplied to the dining area is where the HEX would be applied, just to complete the analogy to your project.

EDIT: I did see the CFM requirements posted above, and OD Temp.

The other part is control. Electricity is fantastically controllable with an SCR controller; infinite and responsive. A good thing.

Weezbo

it depends on the heating strategy of the rest of the building

turning large fans off and on wrecks havoc with the exhaust stream of "Unit heater" forced air ...it would be prudent to watch the process as there are the occasional idiosyncratic behaviour patterns or day to day standard operating procedures as it were , that are Real Eye openers ...

Douglas Hicks

In most jurisdictions, a spray booth must have some kind of fire suppression system protecting the booth, plenum and duct. Additionally, the exhaust air and intake air need to be shut off when the suppression system activates. The fuel supply needs to shut off, fuel gas, electric or whatever the fuel source. The suppression system will have micro-switches installed to trip contactors or shunt trip breakers. If you use fuel gas, I reccommend mechanical gas valves, not electric gas valves. Each time your customer gets a power bump, the electric gas valve will shut off and the pilots will need to be relit.

Fire guy

Weezbo

Mixed air box off adedicated boiler...

that way you can add supplemental heat to the area when the drying fan is shut down.

an automated ceiling heat wall might be a good idea. outside air thru the mixed air box thru the heat curtain filtration of outside air and shop area exhaust air ahead of the heat curtain on varialble speed would probably "waste" as little as possible. Fire Dampers would be required..and what do they currently have for exhaust air filtration in the paint booth?


i read a post or two further down... one thing is the type of chemicals and paints there are operation that do not use certain chemicals instead they go "natural"

then that dove tails into the Fire suppression aspect...and Storage of haz chemicals and flamable ...

you have some ideas however there is way more to the deal than slamming in 250K btu's of some sort and calling it good. Take Brad up on his offer...trust me on this one.

Empire_2

Asking 1 logical question:

Besides the flammability of the products used, Why in such a small booth is there a required 4ooocfm required. I would think that only a positive pressure easily controlled with MUA and well filtered equipment to achieve whatever designed conditions inside the booth. Picture a Lab in Pharmaceutical applications....Although most of their products are not pron to the flammability aspect, they still need Clean, uncontaminated air to allow the product to come out flaw and contaminant free. Usually at a Pos. pressure in the environment or lab.

Mike T.

Michael Welch

Suggestion

Greg
I used to install spray paint booths and conveyor systems for automated spray applications. I am not sure where you are located but you might want to get in touch with Bates Finishing Suply in Littleton Massachusetts. They can help desing the proper air makeup system for a spray application. They service pretty much the entire New England area we Installed equipment for them all over the place.

Greg_40

Michael,

Thanks for the resource. As for some of the other quesions and comments: I only know what the owner has told me regarding cfm requirements of his spray system- he needs 'X' CFM per sq ft of opening to the booth, therefore, he determined the CFM. I understand the supression needs- not our area of concern with this project, but thanks for the head's up. I see a real big Btu hog here, but they do not want to continue stealing air from the production areas of their building for a number of reasons. I will keep researching for a suitable make up air heater for this applicaion. Thanks for the other suggestions, also, it gives some options to condiser in designing the heating unit.

tim smith

wood boiler w/ backup oil burner

I seem to remember seeing a wood burning boiler w/ backup oil or gas burner. Maybe this coupled with a water to air heat exchanger and 100% makeup air might work?? Tim. Another makeup air/paint booth mfr we have worked on many times is Devilbiss. Good product used mostly in body shop work for down draft paint booths. Might be a good resource also.

Kevin_52

makeup air

www.renewaire.com

Marty

already made

http://www.rezspec.com/

Reznor makes a ton of make up air units. Have seen electric ones. Some also for humidity control which may be a concern depending on your location. If this area is only used for short periods of time and if below freezing weather is common I would be concerned about any water based heating setup.

hr

Do your math on the wood boiler, also

scrap wood pieces offer very little heat especially when burned at a 20- 40% efficiency.

Wood furnace manufactures are hard pressed to provide BTU output numbers with such a wide variety of wood types, quality and moisture content.

hot rod

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Greg_40

Hot Rod, that was my concern also, but these folks are trying to make lemonade out of their lemons. The have a large amount of small scrap lumber that gets burned for disposal already. They thought it would be a good energy source. Adding an anitfreeze reduces the heat exchange eve more. If we could get a high degree of filtration, recycling the air would be grand, so there would be minimal pre-heating needed.