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Is there any difference between POE switches and normal switches when budgeting for cooling capacity for a network closet?

Normally, when I'm thinking about cooling; I can look at the power draw of a device and assume that for every watt I dump into the room; I'll need to figure out some way to get that watt out of the room in cooling.

But, with POE switches, they can draw an enormous amount of power, but that power isn't being consumed all in that room. Some of it is going to power the phones or APs (making cooling those "someone else's problem") and some of it is going to heat up the wires.

The question is, do I treat POE switches as though they draw a little bit more than their non-POE brethren? A lot more? Anyone have hard numbers or hard-learned experience?

chris
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  • Check the switch specs, When we upgraded to POE, the BTU output was in the spec sheets. – Zoredache Feb 15 '11 at 18:29
  • Some vendors don't make the information blindingly easy to find while they always make the power draw obvious. – chris Feb 16 '11 at 13:42

4 Answers4

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Nothing from hard experience, but I would take it as a given that PoE switches draw more current than their regular cousins.

Cisco has some numbers for Catalyst 65xx series equipment. To summarize a 48-port 10/100/1000 board dissipates 443 BTU/Hr and the PoE version of that board puts out 518 BTU/Hr (+17%). To be safe I'd inflate the heat load by 20-25%...

voretaq7
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  • Thanks for the link to hard numbers! The difference between the power draw of a POE+ and non-POE device can be 2x or 3x, and that makes a huge difference in the potential cooling required. – chris Feb 15 '11 at 18:17
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We're facing this exact problem as we're deploying POE switches into our edge in preparation for an eventual VOIP project. We don't know what brand of VOIP we're going with, we just know that in the lifetime of these edge switches we'll need to support POE. In the process we had to upgrade the power outlets in many closets as the POE switches need something other than NEMA-15 plugs.

Yes, do plan on cooling for the rated draw of the switches. This is a non-trivial expense, and we had to do it too. It's a future-proofing thing. If money really is an issue and your VOIP project is well down the road, you can defer the cooling upgrade until there is money for it, but you will have to upgrade your cooling.

chris
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sysadmin1138
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3

Yes there are extra cooling requirements.

POE uses more current, current equals heat - so yes you need more cooling (and power of course, in fact choosing the best PSUs for POE-equipped Cisco Cat 65xx's can be more than a 2 minute decision).

As for how much more cooling, well I always say hope for the best but plan for the worst, look at how much power you COULD pull, multiply it by 3.41 and that's how many BTUs you'll need to clear.

Hope this helps.

Chopper3
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The real question here is "how much" more cooling is required. Cisco and APC have a white paper that addresses this exact issue.

Here is the link: http://www.apcmedia.com/salestools/RMEN-65ZRMF_R0_EN.pdf

But the short answer is, Input rated power in Watts X 0.6 is the heat output load. They also give the same information for UPS heat loads. The UPS rating in Watts X 0.09 BTW, be carefull, a "2200 KVA" UPS might be rated anywhere between 1980 Watts and 1540 Watts.

I'm in the middle of this exact exercise myself, and found this page with my Google search. When I got around to closing the window, I had found a few answers that I think might help.

Cheers,

J Roger Marsh RCDD
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