Server room A/C

[Dieselboy]

we have a wall unit in the server room that is fine when it's working, but sometimes it stops actively cooling the air.

Have have some quotes for a new unit and one option is a ceiling cassette like what you find in office floors. My problem with the ceiling cassette is that I must have cool air blowing around the front of the racks to be sucked through and exhausting hot air out the back, which will rise and be drawn in to the AC cycle.
I looked in to the cassettes cool air flow and it seems they normally blow out all four sides, with options to use three of the sides. I have a feeling a ceiling cassette type unit would be much more capable of keeping the room at a stable temperature.

I've never seen this type of unit installed in a comms room though. Has anyone seen this type of setup? Does anyone advise against it?

If we set cool air to blow out 3 or 2 of the sides then it should be fine.

[deanwebb]

I agree on limiting the blowing... what's the exhaust fan like?

[Dieselboy]

Not sure I get the question

We have a 5108 Cisco server chassis, that blows.


SANs and UCS C servers and other things. But I've installed everything so the exhaust is on the opposite side of the current wall mounted system.

Basically I have two goals:
1. I want cool air available at the front of the rack
2. I want to prevent cool air being blown onto the back of the rack, as this will restrict the hot air leaving the equipment.

[deanwebb]

There should be an exhaust fan to draw out the hot air from the back of the rack, to create that airflow.

Put it this way: if you fart in that room, does the smell linger? If so, you do not have good circulation. If you eat a big bowl of beans and go in there and let one rip and there's nary a whiff of the evil deed, then you have proper circulation in there.

The fart test does not lie.

[Dieselboy]

hahahaha I'll have a gas-inducing lunch and do some tests...

The front and rear of the racks are fully metal mesh. So the air comes straight through the rack both front and back when the doors are closed. The sides are solid. The top also has gaps but mainly the air comes out the back.

The room is about the size of a kids bedroom. There's 2 racks with the side of one rack pushed up against the wall, and the 2nd rack pushed up against the side of the first. there's ample space in front and behind the racks.

There's no outside ventilation, really. The room is sort of sealed when the room door is closed. If I fart in there, it's just going to cycle round and round the room. Is the fart test a really good idea in such a small enclosed environment?

[deanwebb]

If it hangs in the air, you don't have a good heat exchange, and that means the cooling unit has to work that much harder, and that means much higher energy bills.

The flatulence test sounds outlandish or like something you tell the junior admins to mess with their heads, but it's for reals.

Having good exhaust will make sure that there's good air exchange. Air exchange will keep the air circulating, so that you don't have heat zones build up that can damage gear, even if the front half is cool.

[Dieselboy]

Thanks mate.

There really isn't a place you can stand in, in the room, that you wouldn't be blown on by either exhausted or cool air. I'd say the air in that room is quite turbulent. The only place where this is minimised is the very side of the rack, where I've put a carpet tile down so I can sit on it if I'm in there . But even then, you get blown on by the cool AC a little bit.

I'll do some more investigation based on your below and see if it can be improved, still. Thanks