Cooling Server Closet - No A/C Is Possible

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.