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I'm trying to cool a little server farm in my rented apartment that consumes around 5kW of electricity. The insulation of the building is crap and there is no central heating so during the winter it kept the apartment at a pretty nice 18C.

Now that summer is coming though, things are heating up. All I have for ventilation is a few 20cm diameter holes that go straight outside, none of the windows open.

I've tried a few fans already, one was a bathroom fan that exactly fits the hole, it turned out to be rather noisy and doesn't really move a lot of air.

Another is a generic floor fan, the blades have a ~40cm diameter, I put a cardboard shroud around it to enclose around the hole as best as I could. That slowed down the fan quite significantly due to increased resistance but it still moves way more air than the bathroom fan and makes way less noise.

Now I've been looking at centrifugal fans online, apparently they should be better at dealing with high flow resistance but are also reported to have higher energy consumption and noise.

Do you guys think I would get better efficiency in regards to air flow/power consumption with a centrifugal fan or an even bigger axial fan?

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  • if you go centrifuge, go as big as possible, and use a motor speed control. large blades move more air at a lower rpm and are thus quieter. I would pull in with a huge squirrel cage that maxes out that 20cm, and push out all other openings with positive pressure alone, no other fans. You can get away with that because cages can handle high pressure; for a smaller fan to increase the amount pushed out naturally would require high RPM and noise, so there's no need to bother.
    – dandavis
    Commented May 9, 2018 at 4:30

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A centrifugal fan should be able to push maybe 300-500 CFM through that hole, it will be fairly noisy and will probably draw 200-300 Watts depending on the size. Maybe something in the 1/6-1/4 HP range. However fans generally don’t do much when they are taking in relatively warm air to begin with. A fan will help a bit but if it gets hot where you are drawing the air from it probably will not be satisfactory. Usually a server room using that much power would be cooled by refrigeration.

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    time for a watercooling loop that has the radiator outside then...
    – ratchet freak
    Commented May 8, 2018 at 8:16

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