Ventilation requirements for automotive repair garages

[96ultra]

I can't seem to find the ACH requirements for a tractor trailer repair facility in NJ. The shop volume is 260,000 cft. The floor area is 3,260 sqft. Fuel will not be dispensed. I recall seeing somewhere that the "recommended" number of ACH is 20-30, which works out to be roughly 130,000 cfm at 30 ACH. Assuming 12 exhaust fans, each would have to exhaust 11,000 CFM. This would present some serious heating and cooling problems for the make up air. Would these run all the time the shop is occupied, or be controlled in some way? Any ideas would be appreciated.

Bill
Engineering Professionals, Inc.

 

[chicopee]

The company that I once worked for had somewhere around 20 equipment maintenance bays and at each bay there was infrared suspended unvented gas heater which you'll find in Grainger catalogs. These heaters were for the comfort of the mechanics and not for the intended purpose of heating equipment. Additionally we had ceiling fans recirculating the unvented heater PoC. Due to the fact that the bays were opened and closed somewhat frequently, there was no one in the shop ever complaining of headaches or sick from PoC. In the event additional heat was required, we had two waste oil burners strategically located in the shop. Also we had flexible metallic connectors to vent the exhaust from the trucks and heavy equipment when testing engines. If you intend to follow the same setup mentioned above, two things that you'll need from the manufacturers since Grainger catalogs may not be adequate, are the fan angular position charts for the infrared heaters and the ceiling fan performance curves or data for varying elevation. Do that before you purchase the equipment. That's the route that I recommend which also worked well for one of our spray painting bay (E25,000 sq ft), heavy steel manufacturing bays (E. 150,000sqft plus) and our precast concrete bays (E100,000 sq ft).

 

[berkshire]

The main thing here is to get the exhaust out of the shop by direct ventilation using slip on exhaust ducts. It gets very cold in NJ and mechanics will be reluctant to open doors unless they absolutely have to. If you have engines running in the shop you will get some heating effect from the radiator rejected heat. In the summer of course when it is 90* you will have the doors open.
B.E.

You are judged not by what you know, but by what you can do.

 

[DrRTU]

Is your volume of ft2 incorrect? This results in an average 80’ tall structure – this will create other challenges with a small foot print.
Will the space require air conditioning for mechanic comfort?
Utilize source tailpipe capture. This can be difficult due to high exhaust or dual on tractors and low exhaust locations on straight trucks. Rails or hose reels are the best. Utilize 300 to 400 cfm per inlet but base upon fuel/engine size. Utility set with VFD driven on main pressure. Harvey rail.
Check local IMC for exhaust requirement. It will run between .75 to 1.5 cfm/ft2 for exhaust. For tractor repair in bays, I would do 2 cfm/ft2 to avoid issues and account for future fuel changes (natural gas). Operate general exhaust in zones based upon CO /NOx/H. Floating stuff is bad with diesel. You may be required to do ½ of general exhaust as low (6”aff) capture. Utilize a minimum .05 cfm/ft2 continuous – we do .10 with breaker on 24/7 to flush out space. Size direct fired MAU based upon total exhaust flow and operate based upon CO/NOx/H.
Utilize low intensity IR for space heating at service bays. 80/20 direct fired can be cheaper but at lower comfort. You will have to do the math on a machine or machines required. We have utilized both vacuum and positive pressure IR and both have worked well. I like gas unit heaters at overhead doors when utilizing IR for mechanic heating.
For air-conditioned facilities 15 and 20 ton RTUs with concentric packages seem to be the sweet spot. You will lose cooling with the CO/NOx/H & MAU is running but it works out.
Evaluate waste oil for floor heating or radiant floors.
I am located in Chicago so the loads should be similar.

 

[trashcanman]

The 2006 International Mechanical Code says to use 1.5 cfm outside air/sq.ft. for repair garage. -Chapter 4, ventilation. In this case, outside air = 3260 x 1.5 = 4890 cfm.
The local code authority may want more though.

Always check to see what the code says before doing a bunch of searching.

 

[96ultra]

I found out from the DCA in NJ that the requirements for a shop like this is 0.75CFM/sqft of floor area. It was tucked away in the IMC under "Storage" of all places.
BTW the volume was incorrect. My bad. That's what happens when you rush. Duh!

Thanks to all for feedback. Maybe I can return the favor some day.

Bill
Engineering Professionals, Inc.