[OP]
Member
Our shop is all in floor heat, so we deal with building pressure issues. We had a crazy thought, that if we could recirculate the exhaust fan air from our spray room through some filters and back into the shop, that we could save some heat. Besides the heat and air pressure, we would consider AC in the shop to keep humidity levels down in the summer. Has anyone done this or have opinions about this?
Contributor
How are you going to remove the VOCs that are in the exhaust air? If you use only water borne finishes the still have small amounts of VOCs in them and the exhaust air might cause humidity issues. Theoretically, you could run the exhaust through a really good filter bank & then a heat recovery exchanger, but that would be $$$$$$$$.
Even up here in the frozen north, I've only seen shops exhaust the air & use a make up air unit to replace it.
Moderator
It may or may not be possible and Frank's comments are important. This is a complex engineering question that has to be answered by HVAC and other experts...and if you are a commercial operations, OSHA is also part of the equation along with local jurisdictions.
--
The most expensive tool is the one you buy "cheaply" and often...
Contributor
I think you would be best isolating the spray room totally from the shop. That way you have two spaces to deal with. They are certainly two different environments. I assume that the radiant was not laid out to allow this zoning based upon the floor plan. I think by the time you recirc the spray room air you will have some whopper $ air filters and with what you are putting through them the replacement would be frequent. Not knowing location and size of the space(s) also make it difficult to advise. Does the radiant do a good job on the heat side? I doubt that the AHJ, fire dept and insurance company would look at your idea favorably.
Contributor
Would an air-to-air heat exchanger have value in your application? I know nothing about compliance, however.
Contributor
I looked into this a little bit when planning my shop (and quickly gave up on the idea). There are commercial recirculating spray booths available but I know nothing about them other than they exist and look like they are mostly for larger installations and look $$$$. But searching for recirculating paint spray booth will get you some links as to what is involved.
--I had my patience tested. I'm negative--
Contributor
do you need to heat the shop? You say you have floor heat. Do you use it? Do you live in Antarctica and heat year round or a more temperate climate and heat only some part of the year? yet another question that including location would help answer. Why do you not have location in your signature?
Summer in the desert no need to keep the heat in the spray room So I do not worry about it here in summer.
Bill D.
Last edited by Bill Dufour; 02-22-2020 at 11:54 PM.
[OP]
Member
Location is in Minnesota cold winters and humid summers, 8500 sq. Ft. Shop, all in floor heat with wood boiler. Our booth is a 18'x18' room in the corner of the shop. 24" fan for exhaust. We were thinking a type of mesh filter screen to grab the larger particles that would go on the inside of the room in front of the fan, then the fan, then charcoal filters, then duct work to bring it back into the shop and possibly like your average furnace filter on the duct outlets. I know Crazy idea.....
Contributor
A unit of sufficient size might be prohibitively expensive, but a heat recovery (or ERV for humidity control as well) ventilator is probably the right general direction. It would allow you to exhaust the contaminated air but still recover ~80% of the heat content.
Contributor
If you want to fab up something get a couple of car radiators or water coils and a circulating pump install one radiator/coil in the exhaust air duct and the other radiator/coil in the makeup air duct. Pipe the two together top of exhaust to bottom of makeup air , top of makeup air to pump to bottom of exhaust. Fill with antifreeze water mix or food grade glycol , wire pump to run when exhaust fan is running. Bigger the radiators/coils the more heat recovered, don't circulate the water too fast use a ball valve to regulate flow also to hold amps down to allowed amp draw per motor nameplate Can be done as inexpensive or as costly as you want to spend.Originally Posted by kyle jarnot
Contributor
The shop I used to work for recently installed an open front recirculating booth about 14' wide x 10'deep x 10'high. Filtered air comes in at the top front of the booth and forms an "air curtain" keeping out dusty ambient shop air, then exits through particulate filters and activated carbon filters. About 10% of the airflow is exhausted outdoors and the rest recirculated. I don't think there is a heater involved, whatever makeup heat is needed comes from the surrounding shop environment. The carbon filters have to be refilled periodically, but the overall heat demand is far less than prior. I believe the installed cost was in the upper 5 figures. So your idea isn't crazy, but the engineering and gear to do it right won't come cheap.
Member
To avoid condensing VOCs on the inner surfaces of the a2a heat exchanger, it would need to be professionally designed & specified for the delta temperature range, flow rate, and the properties of the VOCs and other finishing vapors. Otherwise, the VOCs and residual finish would end up coating the exchanger and reducing its ability to exchange exhaust heat into the replacement air.
Andy - Arlington TX
Contributor
Recirculating brings some air quality issues. How about an inexpensive way to minimize the operating cost?
Careful control of the exhaust volume can help. While spraying you may want to move even more than your 24" fan does now but after spraying a much lower flow is probably appropriate as the material cures.
Close capture of contaminants is also key. This is difficult when spraying but you may be able to do something during cure.
A lot depends on what finish you are spraying and how often and shop occupancy. Also regulations, standards and sensitivity may be challenges.
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