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Background: The server I'm configuring needs to be able to work at altitudes up to 10,000 feet.

Are there any rules of thumb or guidelines on how much faster fans have to spin at altitude (due to lower air density) to provide adequate cooling? Or if I know that my server's fans are going at 50% at sea level, what % will they be running at 10,000 feet?

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4 Answers 4

up vote 4 down vote accepted

Are you talking 10,000 feet in a pressurized airplane, or in the raw environment?

If you mean in a pressurized airplane this is a moot point. Normally those environments stay pressurized at a level "below" 8000 feet.

If you mean the raw environment You're talking about roughly a 4.6psi decrease from sea level (-32%) - but bear in mind that you'll also be in a substantially colder environment (about 2 degrees (C) cooler for every 1000 feet). The decrease in volume of air moved by the fans should be compensated for by the temperature drop.

Of more serious concern should be ensuring that all components (hard drives, etc.) are rated to operate at that altitude - having your server die because there's not enough air to build an "air cushion" for the hard drive heads could ruin your whole day.
At one time it was pretty common for equipment to list a maximum operating altitude (which was usually 10,000 feet) - you may want to check with your vendors.

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Thanks, I meant in the raw environment. –  eglaser Apr 21 '11 at 19:13

10,000 feet is nothing extraordinary, just over 3,000 meters. Lots of cities in Peru are above that level and don't have any higher reliability issue about fans. I've done some work at twice that altitude and I would be surprised if there was an issue even there.

Just be sure that the fans operation is controlled by component's actual temperature and not by RPM tables.

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See http://www.comairrotron.com/high_altitude_cooling.shtml for more information on air density/altitude calculations, however many motherboards have a PID controller built-in that modulates the speed of the DC fan motors to maintain CPU temperature, automatically. If your motherboard doesn't include this, I'd wonder if you're using the right one for such a sophisticated application, but there are third-party PC mods that also have a temperature controller that drive chassis fans, typically for the desktop form-factor (e.g. http://www.newegg.com/Store/SubCategory.aspx?SubCategory=11&name=Controller-Panels)

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You don't need to make any special accommodations for the server directly; but any ancillary cooling systems need to be sized properly for the conditions. If it's just a server or two, nothing special needed. If it's even a small data center, be sure to contract HVAC people who know the differences.

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+1 for HVAC concerns -- If you're building a facility you probably won't want to pressurize the datacenter back to sea level, so it's important that the cooling system be appropriate to the density of the local air. 10,000 feet is high enough that special considerations could be necessary. –  voretaq7 Apr 21 '11 at 19:05

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