Roof Top Classified Air Conditioners
Roof Top Classified Air Conditioners
(OP)
We have an explosive (class 1 Div 2) building that has to be air-conditioned. The air-conditioning units will be placed on the roof.
The problem is that the air conditioning unit will suck the explosive gas from inside the building, and so the roof top air-conditioning unit should also be classified.
I have been searching but am unable to find classified roof-top air conditioning unit. What should be done in this situation? Suggestions will be appreciated...
The problem is that the air conditioning unit will suck the explosive gas from inside the building, and so the roof top air-conditioning unit should also be classified.
I have been searching but am unable to find classified roof-top air conditioning unit. What should be done in this situation? Suggestions will be appreciated...






RE: Roof Top Classified Air Conditioners
RE: Roof Top Classified Air Conditioners
A chiller circulating cold water through the air handling units may work also.
Bill
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"Why not the best?"
Jimmy Carter
RE: Roof Top Classified Air Conditioners
My main question now is whether we really need explosion proof air conditioner or not. The code says that only 5 feet around the equipment should be classified. Do we really need the explosion proof air conditioning units (on the top of roof), or is it overly conservative? Please let me know comments.
RE: Roof Top Classified Air Conditioners
RE: Roof Top Classified Air Conditioners
RE: Roof Top Classified Air Conditioners
RE: Roof Top Classified Air Conditioners
RE: Roof Top Classified Air Conditioners
RE: Roof Top Classified Air Conditioners
RE: Roof Top Classified Air Conditioners
Is it correct?
RE: Roof Top Classified Air Conditioners
Section 513.3(D)is somewhat complementary.
From 513.3(B), the hangar area is always Division 2 up to 18" above the floor ventilated or not.
In any case, ventilation of the overall hangar can only help. The Division 2 envelope is only 18" above the floor and 5' from the aircraft power plants and fuel tanks [513.3(C)]. As long as the air supply source is outside the envelope ('you gotta draw the line somewhere') you can ignore the area classification for the HVAC.
RE: Roof Top Classified Air Conditioners
I am not saying that you are wrong; just I am looking for more clear explanation.
RE: Roof Top Classified Air Conditioners
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If we learn from our mistakes I'm getting a great education!
RE: Roof Top Classified Air Conditioners
RE: Roof Top Classified Air Conditioners
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If we learn from our mistakes I'm getting a great education!
RE: Roof Top Classified Air Conditioners
RE: Roof Top Classified Air Conditioners
RE: Roof Top Classified Air Conditioners
My concern is that the classification suggested in NEC is only for non-air-conditioned hangars. But in our case we have an air-conditioned hangar. So the entire hangar from floor to ceiling should be classified (instead of only 18" above the floor). Is it correct?
RE: Roof Top Classified Air Conditioners
RE: Roof Top Classified Air Conditioners
In other words, the roof top air-conditioner will suck the explosive gas from hangar, and will make it cool and then throw back into the hangar.
The explosive gas will be displaced in every cycle, and will keep moving throughout the hangar. So the whole hangar should be classified??
RE: Roof Top Classified Air Conditioners
RE: Roof Top Classified Air Conditioners
Back in my days at Boeing, I was assigned to 'clean up' the design of a prototype automated tester for aircraft electrical power systems. Basically, it does a functional test of the electrical generating and distribution system on each airplane under construction. One component of this wheel mounted collection of equipment was an electrical load bank, consisting of 60 kW of resistive elements (exposed heating coils), contactors and a big fan. The people (not very bright) who built the prototype ATE mounted the load bank with its air intake at the bottom within 18" of the ground. And since there was the possibility that this unit could be used on the flight line, or in a hangar with fueled aircraft, this was a big problem.
My solution (after checking with our fire dept. and safety people) was to flip the load bank upside down. So it sucked in fresh air at the top (6' above ground) and blew it out at the bottom).
RE: Roof Top Classified Air Conditioners
RE: Roof Top Classified Air Conditioners
Subsection 515.3(B) does. That's why I said to ignore the title. From a "grammar" standpoint, read the sentence without the parenthetic clause - and note the parenthetic clause would not change the hangar floor's status.
Ordinarily, the area below 18" isn't volitile either - that's fundamentally what Division 2 means. See Section 500.5(B)(2); especially Subsections (1)&(2).
RE: Roof Top Classified Air Conditioners
Does this also apply to both air-conditioned and non-air-conditioned hangars?
RE: Roof Top Classified Air Conditioners
RE: Roof Top Classified Air Conditioners
In the absence of air conditioning, the explosive gases will be present only up to 18" from floor level.
My whole point is that the air conditioning will "force" the explosive gases to move. And so the whole building, from floor to ceiling, will become explosive (instead of only up to 18")
RE: Roof Top Classified Air Conditioners
I don't believe I'll waste any more time on this. See Section NEC 90.3(C)
RE: Roof Top Classified Air Conditioners