Cooling Server Closet - No A/C Is Possible

Question

We're moving into a new office in an old building in London (that's England :) and are walling off a 2m x 1.3m area where the router & telephone equipment currently terminates to use as a server closet. The closet will contain:

• 2 24-port switches
• 1 router
• 1 VSDL modem
• 1 Dell desktop
• 1 4-bay NAS
• 1 HP micro-server
• 1 UPS
• Miscellaneous minor telephony boxes.

There is no central A/C in the office and there never will be. We can install ducting to the outside quite easily - it's only a couple of metres to the windows, which face a courtyard.

My question is whether installing an extractor fan with ducting to the window should be sufficient for cooling? Would an intake fan and intake duct (from the window, too) be required? We don't want to leave a gap in the closet door as that'll let noise out into the office. If we don't have to put a portable A/C unit into the closet, that'd be perfect.

The office has about 12 people; London is temperate, average maximum in August is 31 Celsius, 25 Celsius is more typical. The same equipment runs fine in our current office (same building as new office, also no A/C) but it isn't in an enclosed space.

I can see us putting say one Dell 2950 tower server into the closet, but no more than that. So, sustained power consumption in the closet would currently be about 800w (I'm guessing); possibly in the future 2kw.

The closet will have a ceiling and no windows and be well-insulated. We don't care if the equipment runs hot, so long as it runs and we don't hear it.

Solution 1

Well, let's work this out;

• 2 x 24 port switches (say Cisco 3750-E's) can output 344 BTU/hr each so that's 688 in total
• 1 x router (say a Cisco 2921) can output 1260 BTU/hr
• 1 x VDSL modem (say a Draytek Vigor 2750) can output 120 BTU/hr
• 1 x Desktop (say a Dell Optiplex 790, with monitor switched off) can output 850 BTU/hr
• 1 x 4-Bay NAS (say a Netgear ReadyNAS Ultra 4 with 4 x 2TB disks) can output ~600 BTU/hr
• 1 x HP Microserver can output 511 BTU/hr
• 1 x UPS (say an APC Smart-UPS 2200VA that can handle the ~1.2Kw you may be drawing) can output 275 BTU/hr

That's 4300 BTU/hr.

You've got 5.2 cubic metres of space (minus the items inside it), so not including natural heat loss you're going to have to install a minimum 29cm fan with a 900 cubic metre per hour rating with 29cm conduit all the way to the room if you don't want to hit 42 degrees C (the lowest recommended highest temp of the kit listed above) from a nominal of 20C in 17 minutes.

Basically get an external A/C unit that can scrub 5k BTU/hr ok - a fan's going to literally and figuratively suck :)

Solution 2

Get a small split system AC unit, like the Mitsubishi MSY series (no affiliation, used them before and like them). They're very small, quiet, reliable, and reasonably affordable. Two pipes will have to be run outside (roof or similar), they're small (3/4" and 1/4" roughly). The unit will cost around $2000 USD, and less than half that again for installation (depends on the specifics but it could be much cheaper).

Solution 3

When keeping things absolutely quiet is the top priority over keeping your equipment in good working shape, and the proper housing of equipment can't be considered, I'd strongly look at outsourcing your server needs or running fiber/high speed connections to a proper data center or facility.

Otherwise you risk looking at costing more in periodically replacing equipment than it would have cost to properly protect it in the first place.

It will be nearly impossible for someone to tell you it'll be just fine with a general statement of "it's usually this temp in the city each year," etc. because what about airflow? What about what your office mates insist on setting the thermostat in the office, and that temp flows into the closet? What about processor load on your switch and servers?

Even with a server of XYZ specs, the temp it runs at differs based on airflow through a rack, through the room, and what load we place on the power supplies/processor/hard disks. In other words, we wouldn't know until it's in the room running in real-world conditions. And you're describing a situation where you can easily find yourself overheating equipment because someone doesn't like the humming noise from the room.

Solution 4

Unfortunately, the realities of thermodynamics are crashing full speed into your environment. If the closet isn't big enough to absorb and radiate out the heat, then you need to mechanically get rid of it. There are, in fact, some experimental data centers that do simply cycle exterior air without additional cooling, though they tend to be in rather temperate and dry climates. London, however, is not exactly known for its low-humidity and mountain fresh air.

What you really need to do is install an air conditioning unit for that room. There are lots of solutions out there. The one I have the most experience with is the Mitsubishi Mr Slim line. We've used them to great effect in exactly the same situation you're finding yourself in.

Solution 5

The 2950 is a 2u rack server, I'm wondering if you are meaning the 2900?

I've run both of these at home in a room (converted garage) with no a/c or ventilation and they both warmed the room noticably after a few hours of usage.

For a production envoironment, I would have to suggest a/c, even if it is tricky - think about an unexpectedly hot summer day.... (Really for a production envoironment you should also have a backup a/c unit). The poweredge rack mount units are really designed to be in a data centre with decent cooling.

As an absolute minimum, seperate intake/extract fans, although it's not unknown for summer to hit 37/38°C in London, and there could be localised hotspots being slightly higher.

I believe there is an overheat threshold of around 65°C on some device in those servers (you may wish to verify the exact temp yourself), and 40°C air will not cool them down at all well compared to nice air conditioned air (the 9G servers also had FB-DIMM's which can run pretty hot, SAS drives if fitted also add a fair bit of heat compared to SATA).

If you really are not allowed to install a/c, I would suggest a decent envoironmental monitor which can send you a SMS message in case of problems, and settle on your callout rate to attend site out of hours due to thermal issues. Once this price is settled, suddenly the cost of a/c may not seem so bad.

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Comments

[Kcmamu]

Why the downvote? I can see why the proposed idea isn't liked, but that doesn't make it a bad question! +1 to counteract the needless down vote.

[Zineb Farhat]

Thanks, Bryan. Yes, this may seem a silly question for those who have lots of experience with server-rooms, but for small offices with small budgets, this is an actual problem, so please don't think I'm trying to waste anyone's time. The answers below are really, really helpful!

[user1364702]

I wouldn't say you're wasting time or anything like that (although it would be nice to know why it was downvoted...) From the framing of the question, you're being told by TPTB that silence is of utmost importance. So you're in a bad place...do you want reliable equipment and data storage/switching, or do you want to risk inconveniencing some people? They need to let you do your job and keep them able to do their jobs. Right now they're compromising this and making your life harder.

[Kcmamu]

@JamesCo, on the contrary, I don't think it's a silly question at all, I think its a good question, I've been to many customers with similar set ups. I'm just surprised that another serverfault user decided to down vote your question, which I can only assume was because they didn't like your proposed idea of not using A/C. You certainly aren't wasting anyone's time, we frequent this site to help each other out after all!

[Zineb Farhat]

Hi Bart, the DC VM is backed up to the NAS, offsite to disk and offshore to Paris. It's running on a whitebox ESXi server 'cause the Dell 2900 we had was too loud. It's only a DC for this office, so not mission-critical, but you're right: it shows we don't have the (human) resources to always get things 'right', but that's another topic ;)

[user1364702]

Have your office people considered noise-canceling headphones if they have a problem with white noise?

[Zineb Farhat]

The programmers can wear noise-cancelling headphones all day because no one talks to us, but for the rest a low background noise-level is worth seeking. In a quiet office people talk more quietly, which is something ours could do with...

[Thomas Eding]

Use ice. And lots of it.

[James Moore]

People and silence are FAR more important than extending the life of the equipment. Suggesting headphones as a solution is just bizarre.

[Adam Davis]

Keep in mind that this is simply your current setup. It's quite likely that equipment will be added to it over the next few years, and installing AC later is going to be significantly more painful than simply doing it right during the initial buildout.

[Rob Moir]

My experience of bosses that tell you that silence (or cost or sticking with "crazy joe's place of cheap PCs" brand of home brew servers because the boss went to school with crazy joe or whatever) is more important than using the right gear will suddenly change their minds when a disaster strikes and not only decide that not only should the right gear should have been used all along, but that its your fault it wasn't for not framing that in language they can understand.

[Zineb Farhat]

An oil bath is too ambitious for our small office, and some stuff (e.g. the telephony) is bolted to the wall. If we vent at the bottom of the closet then it means venting from the general office-space, which we want to avoid as it'll mean noise escaping. Thanks for the answer!

[Zineb Farhat]

That's a good idea for outsourcing any server needs. Our Dell desktop serves as a local domain controller (running in a VM) which is the only essential onsite server. We can install ducting for extraction and intake to the window - it seems a stupid question, but both are necessary, if the closet is otherwise air-tight?

[SmallClanger]

+1 for this. I use a split Mitsubishi system in our comms room and it's as good as silent next to the hum of the servers themselves. They're also rated for a 24-hour duty cycle, something that you might not be able to say for a typical extractor fan or combined unit.

[Zineb Farhat]

That's a fantastic answer (though not what I wanted to hear! :) - thanks for taking the time to analyse the problem.

[Chopper3]

"Top Geek! The most effectual Top Geek! Who's intellectual, close friends get to call him T.G., providing it's with dignity" :)

[Piotr Kula]

Really technical answer and really this guy should be installing this for you. But i suspect getting a fan with temperature regulated speed (and 1 or 2 sensors in the cabinet) with possibly alarm will be good. Because UK is mostly cool during the year try to intake air from outside, via a HEPA filter to remove dust particles. Disposed air should go outside too as it can cause office sickness because of the dryness of the air, but its not necessary. Remember air flow should be cold intake on bottom, warm outlet on top. We have run similar ones in Manchester without AC.. no probs.

[Chopper3]

From near Manc myself, in fact if this was there you'd need to put a heater in the room for all but two days a year to stop the fans from icing up :)

[Dan Is Fiddling By Firelight]

Could you add the formulas you used to calculate the rate of temperature rise without ventilation, and how you calculated the fan size needed to maintain the temperature within the hardware limits.

[mgjk]

Those are maximums. If you're consuming 800W of power, you're not going to produce more than 800W of heat. 2700BTU. By my rough calculation, you'd need to exchange 223cu m/hour of air to keep the rise at 10 degrees Celsius. With those numbers, it's roughly a medium sized kitchen range fan (running perfectly with a very short hose!), and there would certainly need to be an equivalent intake fan to keep the air supply going. 100% agreed that A/C is necessary to futureproof, but if they're not going over 800W, they'll be okay with fans. Please correct me if I'm wrong(!)

[Chopper3]

I did go off maximums certainly

[安辰 anchen]

Great answer, I've seen similar setups where all the equipment is in such a closet. Also, A split A/C unit doesn't require the window to be open and doesn't leave a 23cm tube going out the window.

[nickgrim]

Two fans at the top of the closet, and run ducting from the suck-cold-air-in one down to floor level?

[Deepak Mourya]

+1 I know a lot of smaller companies do this not only due issues with space, but because they usually move their offices a lot more than larger companies. Needinig to move and set-up your servers everytime you move is more trouble than it's worth.

[Chopper3]

@DanNeely - to be fair, after I worked out those basics (no shortcutting that I'm afraid) I put it into a Computational Fluid Dynamics package designed for data centres and it did the rest - can't take full credit for it.

[warren]

@Chopper3 - is that CFD package available to the general public, or a commercial app?

[Chopper3]

It's a very spendy one we bought sorry - we have LOTS of very big data centres so it comes in handy every so often, no harm abusing it for SF users though :)

[Tim Brigham]

Damn... Nice answer chopper3. Wish I had that kind of know how available to me when I was dealing with these kinds of situations.

[Jon]

Oh, and to address noise, it's not that bad. I spend time in the room without hearing protection and can still hear myself think/talk just fine. We've got an office that shares a wall with the "server room" (with next to no sound proofing) and you can hear a faint fan noise, nothing major though.

[sarnold]

Pity you hit the 200-point rep cap some 41 votes ago, this one's good.

[Chopper3]

I'll get by but thanks for caring

[juwi]

+1 for not taking the credit about how you got to your first (already awesome) answer @Chopper3. You totally should take credit for it ;-)

[gWaldo]

@Chopper3, Dropping Science!

[Ben Voigt]

Why do you want a fan at the bottom? If you dump cold air in on top, it will naturally sink.

[Lucas Kauffman]

yes but you will suck out some of it as well, it's just better to suck in cold air or have a hole in the bottom than another hole in the ceiling.