Sub-floor Cooling

Hi all,
We have a number of DCS, PLC, etc. cabinets in a rack room with a computer floor and cables coming from below. It has been suggested that we duct all
the air conditioning into the sub-floor, using it as one great plenum, and then letting it flow upward through the equipment and out at the top. It seems that this would direct the coolest air exactly where it would be needed most.
Have any of you tried this or heard of it? Is this a good idea or is there a hidden catch that will make us regret it?
Walter.
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Out the top, then where?
If you were in the USA, you'd need to study Article 645 of the National Electrical Code, which covers your specific case.
Among other things, it requires that the air conditioning system be dedicated _only_ to the computer equipment, that the room be isolated, fire- wise and ventilation- wise, from the remainder of the building, and that your power wiring must be pretty completely jacketed in metal.
I.e., absent countermeasures required by the Code, the ventilation system provides a forced draft to any developing fire, common nonmetallic insulation constitutes fuel that also produces toxic smoke, and there's no shortage of heat sources from any single point of failure in an electrical power distribution system. All points of the fire triad are present or one mistake away.
Yes, it's been done. It's a good idea, from a cooling perspective. From other perspectives, a little caution would be appropriate. Check the Canadian equivalent of the NEC. Better, hire someone who knows it chapter and verse.
-Mike-
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all
there
Walter, to add to what Mike wrote - I have heard of this but never seen it used. The main problem is the likelyhood of stuffing every component in every rack in the room in the event of smoke in the sub-floor (usually drawn in from elsewhere in the room/building).
Computer room installations I have been involved with (data centers for two of the major banks here - don't ask - we got involved for reliability reasons ;-) use *individual* fire-rated sub-floor ducts to each rack from an package A/C unit sitting in the corner, and a VESDA system sensor installed at the top of each rack to shut rack ventilation down fast at the tinest whiff of smoke...
I hope this helps, Cameron:-)
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Fire protection gas extinguishing system may also be ducted this way.

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Yep - but it's usually piped separately into the bottom of each cabinet, because if a smoke sensor detects nasty things happening in only one rack, you don't want to flood everything else in the room with Halon or FM200 or something equally expensive and nasty.
The other thing I forgot to mention is that you might like to have individual power isolation on your rack cabinets so that you only lose the smoking one - not the entire room. The most common way to do this ("No Smoking" signs don't cut it - cabinets can't read! ;-) is to feed power to the cabinets via a Static Switch and drive the switch's Enable input from the fire panel/VESDA system zone output relay... but that is Big$ to do properly and may be overkill for your application.
Cameron:-)
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