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Adamb 08-17-2006 11:50 PM

Data Center - Air Speed at 1m & 1.8m

Im wondering if anyone knows what the recommond air speed should be in data centers at 1m & 1.8m? At floor level the air speed is generaly at 2.00 meter per a second.

At our data center we have good air flow at lower heights but as soon as you start moving your way up the the air speed drops a great deal. So much so that there is no air flow.

We are in the middle of a data center refurb with 2 new air cons getting installed shortly.


KenB 08-18-2006 12:48 AM

I've never heard of anyone managing data center air speed -- but that doesn't mean nobody does it!

In my experience, the key factors are static pressure and cfm. Depending on who you talk to, you'll need 120-150 cfm per kW of rack load. If you're not supplying that through the subfloor, you'll have hot air recirculating around or over your racks -- a process I call "rebreathing" -- probably to the intakes of systems mounted higher in the rack. Another ineteresting problem is that racks near the air handlers get less air, due to the Bernoulli effect.

You can hire someone to survey your data center and make recommendations about how to cool hot spots and improve airflow to your servers. If you can't find anyone in the Advertising section, let me know and I can recommend a few.

Adamb 08-18-2006 01:05 AM

I should of pointed out that i am from Australia.

Thanks for your help KenB, i will take it on board

Adamb 08-25-2006 09:35 PM

I just thought there would of been some sort of recommendation of how fast the air should be coming out of the floor to reach the servers at the top of the racks...Or am i just talking rubbish?

Maybe someone knows the recommended temp at certain levels of a rack?

Adamb 08-29-2006 04:54 AM

Found this website -

They recommend airflow to be 3 - 4meters (10 to 13 feet)per a second. Any thoughts on this?

RDM 11-16-2006 03:28 PM

I've been looking into this myself recently and found that if you have an air flow of 0.8m/s at the top of your rack at the cold isle side, this should make a cold air curtain which in turn prevents the hot air returning into the servers.
Another point which is more important is that if your crac unit distributes say 18,500 m3 per hour of air, you should have enough perforated tiles that equal this amount. Therefore if you are using 350m3 p/h tiles, you require 50 of them in the room. This relieves the overpressure under the floor making your Crac units more efficent and giving you more balanced airflow throughout your racks.

Mad_Reilly 11-18-2006 03:18 PM

There has been alot of discussion about this issue especially with the increase in rack power densities. Trends have been shifting from typical 20t CRAC blowing air either undrfloor or blowing up to "above isle cooling" and even cool rack solutions. To address your problem(s) though, is this an adverage reading across your facility or is it just in one specific area? Where you are getting this reading, how are the racks pouplated? I agree, racks closer to the air unit recieve , sometimes, less air than racks father out. Obvously, you facility must be getting denser (rack quantity / w per sq ft - sorry meter mate) thus the upgrade. You could have a simple soultion such as adding additional units or it cold be a more complex one. Check out your power loading across your PDU's and compair it with your temp / air movement reading. You can change readings just by rack placement. Just some quick ideas, we do case studies like this all the time. There's alot of good information and white papers on this subject. Good luck

Adamb 01-03-2007 06:06 AM

Thanks for your replies guys. At the moment we are slowly replacing our 25 year old crac units with new 100kw stulz units. We have installed 3 and there is from memory another 6 or so to go.

We have noticed a drop in temperatures around the room and also an increase in velocity.

Also what air vents do you guys use? At one site we use grills and are about 1/3 the size of a tile.

Our other site which we rent they use floor tiles which is covered in little wholes to allow air to come up.

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