I'm trying to figure out how much cooling capacity we need
for our small machine room. The numbers I'm getting seem
absurdly high, so I thought I'd run it past the denizens of
this newsgroup and see if anyone has any suggestions.
The room is 9 ft. x 17 ft. x 10 ft. high. There's no drop
ceiling or raised floor. Two vents from the house A/C
discharge into the room, and there's a return vent venting
into the drop ceiling in the hallway. It's not a designed
machine room per se; it's more of a big closet that we're
using to hold our racks.
There are 4 long flourescent bulbs in the room, which I
suspect don't add much to the heat load.
We've got two racks of hardware, a couple of small desktops
and a CRT monitor. One of the racks is about 2/3 full of
various pieces of network hardware -- PoE switches, switches,
minihubs, CSU/DSU, and a couple of breadbox PCs that are our
The other rack is pretty much full of servers, most of which
are 1U servers whose power load is 560W and whose specs claim
a BTU rating of 2750 (which seems a bit high, but that's what
the specs say).
When we were relying on just the house A/C vents to cool the
room, it was always very warm in front of the racks, and
downright hot in back of them. When the temperature behind
the racks hit 100 deg. F and the HDD temperature monitor I
was running on one of the desktops hit 54 deg. C, I decided
it was time to do something about the problem. I called Spot
Coolers and described the situation, and they suggested a
1.5-ton MovinCool unit, which we agreed to. We ran 12-inch
flexible plastic ducting from the cooler to the return vent.
The unit managed to get the temperature in the room
(according to its thermometer) down to around 74 degrees, and
the temperature behind the racks got down to around 80. Then
we turned on a few more servers, and now the room temperature
is hovering around 79 and the behind the racks it's up to
around 90. I find it hard to believe that the few servers we
turned on made that big of a difference, so I suspect that
there are other environmental differences going on, although
I'm not sure what they could be.
Since we would ideally like to keep the room around 68
degrees, clearly the 1.5-ton unit isn't big enough. The
question is, how much capacity do we need?
I took an inventory of all the hardware in the room and
recorded from each item's specifications the BTU if given or
the wattage * 3.5 (a metric I found in several places on-line)
otherwise. When I totaled everything, I got 75,103 BTU, or
6.3 tons. I find it extremely hard to believe that less than
two full racks of hardware can generate that much heat, but
perhaps I'm hearkening back in the days when most servers only
had one CPU :-).
I guess the question I need sanity-checked by the experts here
is, can two racks of hardware reasonably generate that much
heat? If so, and we want to leave open the possibility of
adding a third rack of hardware to the room, it seems to me
that we're going to have to get a 10-ton unit. Are there even
10-ton coolers that'll fit in a small machine room?
Thanks for any help and advice you can provide.
Help stop the genocide in Darfur!
Click to see the full signature.