Lo-tech A/C for a computer server room
DaveInCalgary
| Posted in Construction Techniques on
I want to provide A/C for a 4000 cubic foot computer server room. We considered several automated systems that look very effective and reliable.The problem is finding installers who can do the work now, as we need the system yesterday. The computers are already running, and when summer hits, an A/C failure would be devastating.
I am now considering a more low-tech approach: putting in two or three redundant ducted household A/C units. My thought is the units will be simpler to install service by HVAC people with less specialized training.
Any idea where I can find out more about following this approach?
Replies
First thing to do is to figure out how much cooling you need based on the total wattage consumed in the room (including lighting, any ventillating fans, etc). Add this need to the basic cooling needed for the structure, a la Manual J. Figure out what combination of units would handle the load, with sufficient redundancy.
Next, does any of the equipment need special ducting? Do you need cold air under a raised floor? If you have very much of that you should probably get a specialist.
Otherwise, it should be a "relatively simple" job of getting even air distribution through the room, and arranging appropriate redundancy. For instance, if you have four units it would probably be best to divide the room in half and have two units serve each half. Each unit has it own supply ductwork (though shared return ductwork may work out). Each pair has two thermostats (or a single double-setting thermostat), one set 3-4 degrees above the other. From time to time swap thermostat settings to even out the wear on the units. In each area at least one fan should be set to run continuously.
One point to worry about is humidity. With ACs running continuously the humidity could get too low, requiring auxilliary humidification. Oversizing the units to a degree will help prevent this, but you need to be careful not to go too far in the other direction. (This is an area where that fancy automated system may have some advantages.)
"One point to worry about is humidity. With ACs running continuously the humidity could get too low, requiring auxilliary humidification"
Dan,
It's a computer room. Why would you want to ADD humidity?
Quantum materiae materietur marmota monax si marmota monax materiam possit materiari?
Static electricityRebuilding my home in Cypress, CA
Also a CRX fanatic!
Precisely.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
It's a computer room. Why would you want to ADD humidity?
Dunno, but the old Amdahl air-cooled units required that you supplied air at 50º and 15-20% RH. While very nice for the humern beans on the raised floor, as air exiting the units was 72-75º; it did make for a mechanical wrinkle in getting the hvac people to monitor RH on the raised floor input side (or down the manifold, for flex systems).
Electrical things produce quanta of ozone based on a whole bunch of things I rely on EEs to tell me about when I need to know. The ozone, and the effects of air cooling modify moisture content in funky ways that the merlins in ME & EE are far far better oriented in the lachemic mysteries of such things. I'm only just smart enough to know to ask in advance.Occupational hazard of my occupation not being around (sorry Bubba)
You may also need to connect the HVAC to the fire supression system, if you have one, so that if the system activates, it shuts down the HVAC so you don't dilute the supression gas with fresh air and start the fire back up.
Yeah, in any event, the system should be set up to shut down the fans if a fire is detected.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
If you don't want to pay for a Liebert or something similar, try a ductless split. But you might not like the price.
This is something you really want to get right the first time. Figure out the cost of downtime, a Liebert might look real cheap.
4000 cubic foot... is not a big room... 20 x 25 w/8ft ceiling... ?
pretty sure i'd look into mini splits/ductless without the heat generated from equipment... you are only looking at needing 12000 btu's i don't know the heat generated from the equipment...
I'd look at 2 maybe 3 1.5ton mini split units you can get em on ebay for about $800ea... (or less) precharged with linesets... only require a 2" hole in the wall i don't see why one wouldn't do what you need... with a second set up on a magnetic contactor controlled by a thermostat set to kick on if temps got above 77degress or somewhere close... you could even have a 3rd set to kick on if temps got to 80...
a local research hospital has this kind of set up where they keep the rats... after they all got killed by heat and wiped out years of research & testing
p
Thanks everybody for your advice so far. The heat in the room is coming from three server racks. There has never been a need for heat. Last summer under a smaller computer load, we had a 12000 BTU portable A/C unit running non-stop, and we only managed to keep the temperature down to 22C (72F) and now there's probably twice as much computer equipment as last year.If there any more ideas out there about sourcing information on this, please share. I'm an electrician by trade, but somehow I think I'm the one one who'll be stuck doing the installation. That's part of why I'm trying it simple.I want it to be set up so as soon as you "plug it in" it's energized, so to speak, i.e., no manual starting required. I'm thinking it will be two or three simple ducted set-ups, controlled by thermostats, and energized via timer-controlled disconnects. Then they'll switch off duty, and back each other up in case of failure.Thanks again for all your advice
It will be connected to a BMS system, but that's further down the road. Fire supression right now is limited to a halon extinguisher, but when the BMS goes in, the A/C control will be interconnected with the alarm system.
Check with SAIT. Maybe some students could do the hookup on a couple of splits?
Well, it's good you're the sparky, since you can figure out a control system. Unfortunately, it's hard to find the pieces of a small relay control system that will go together nice without a lot of hand work.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
We have an engineer to source the BMS stuff. I was pushing for an Allen-Bradley SLK500, because my experience is mostly industrial, but they're going with a product that is more "computery".
We used this wall unit for our server room. It was a very easy retro-fit.
http://www.fujitsugeneral.com/wallmounted.htm