[Seattle-SAGE] Server room build questions

Jeff Silverman jeff at commercialventvac.com
Wed Apr 27 20:57:24 PDT 2005


Scott McDermott wrote:

>Paul English wrote:
>  
>
>>So on to the questions:
>>Given a commercial office space, does a roof-mounted AC make the most 
>>sense?
>>    
>>
>
>We have ours in the computer room, but I wouldn't make this call off handed.
>There's a lot of variables that'll affect what makes the most sense for your
>environment, including what local building codes require. I would definitely
>talk to a good air conditioning company to help you with this (for my 2
>cents I'll recommend Pacific Air, they have some very good people and I've
>been very happy with them.)
>  
>
At the EE department, we had 100% redundant air handlers in the computer 
room, so that either unit could go down without a problem.  The air 
handlers connect to a common chilled water circuit which went to a 
chiller on the roof.  The system works well

>  
>
>>What are people's feelings on raised floors vs. tiles/anti-static carpet? 
>>I'm very opposed to running network/kvm cables under floors (give me a 
>>ladder rack any day), but raised floors can be handy for routing AC to the 
>>front of the racks and running fat trip-causing power cables. 
>>    
>>
>
>I say ditch the raised floors. Since cold air falls, (presuming the rest of
>the space allows the option), you can have vents in the ceiling in front
>your racks and you'll do fine. And adding raised floors to a space that
>doesn't already have raised floors will certainly not be worth it!
>  
>
I agree - raised floors are outmoded.

>  
>
>>How much AC should I spec - get the maximum capacity 20 rack's worth now, 
>>or get a lesser amount now and plan to upgrade? 
>>    
>>
>
>Figure out how many BTU your equipment generates per hour and feed it to
>your AC company, letting them know your projected growth and let them help
>you make an intelligent decision.
>  
>
According to the UNIX units program,  each kilowatt of power going in 
generates 3412 BTUs/hr of heat.  Each kilowatt requires .28 Tons of 
cooling.  A trivia note: in the units program, a ton of refrigeration is 
a tonref.

>  
>
>>Should I spec out a backup AC? Or just plan on shutting down all of the 
>>non-critical systems in the event of an AC failure. 
>>    
>>
>
>Will your non-critical systems shut themselves down if the AC goes at at
>2am? Will your computer room be 110 degrees when someone finally shows up to
>the office? Will the non-critical systems have weathered it without a hitch
>and the critical systems failed horribly leaving you to discover that your
>backups aren't quite as good as you thought? (Not that I'm bitter...)
>Seriously, though, this is more of a cost/benefit issue, and will depend on
>how many tons of cooling you need and how much money/space you want to
>devote to it. We have a backup cooling system now, and we also have a
>netbotz monitoring the environment that starts paging people if it gets
>warm. That said, if you have a good quality AC system, you probably won't
>have any issues. (The one we had fail did not fail in this category.)
>  
>
Probably, you should set up your non-critical machines to shutdown 
automatically if the internal temperature reaches a certain point.  I 
don't know how to do that, but I know it can be done.

>>How much power should I spec? On this one I'm fairly sure that I should 
>>probably spec the full 20 rack's worth (200A?) and just get the breaker 
>>panel put into the room with circuits sufficient for 6 racks. 
>>    
>>
A rule of thumb: each rack has 42 Us.  If you have 42 1 U servers, each 
drawing a couple of amps, then that is 84 Amps/rack.  If you have 6 
racks, then you need 504 Amps, so the 500 Amp estimate is probably 
pretty close.

>
>I really like the APC ISX system, myself. In fact, I can't recommend it
>highly enough, myself. (Though I'm told you should stay away from the
>managed power strips that let you remotely power equipment off. I have no
>experience with those units myself, but have heard complaints about them
>from at least two people, though one said the problems seem to be fixed with
>the newer units.)
>
>You can buy the ISX for your needs today, and grow it over time with
>additional modules to increase capacity and runtime. It's not necessarily
>the cheapest solution up front, but it'll certainly be cheaper than buying
>everything you need for the future now. I also think it has more life in it
>than your usual UPS system. Mark Machkatel at AC Power in Redmond has worked
>with several SSG people before (some with requirements that make yours and
>mine trivial) and can help you with this part of your datacenter.
>
>  
>
>>What are the considerations for a backup generator vs large (Liebert?) 
>>UPS? I'm leaning towards an auto-start generator right now, with small 
>>rack-mount UPSen on the 24/7 critical systems. 
>>    
>>
>
>You should have a UPS on all your systems, even if it's only for short
>runtime. That'll protect your equipment while the generator kicks in. Either
>that or a really large UPS. That's sort of a balance you have to find
>between cost, hassle, and how many power outages the area your in has.
>
>  
>
>>Do we bother with a fancy dry fire supression system? Seems like a major 
>>PITA and would take a big chunk out of the budget for everything else. 
>>    
>>
>
>I recommend against the dry suppression systems. Look into fine mist water
>systems. I can't say how they compare in price to dry systems, but they are
>not a hazard to humans and will do less damage to your computer systems. All
>you'll need to do is dry your systems out and fire (ha!) them back up. With
>the dry systems you'll actually have to have your systems cleaned...
>
>  
>
I recommend against a CO2 system - they are lethal.  If one of those 
systems goes into alarm, you have a few seconds before the CO2 
concentration will knock you out and kill you.  Halon is better if you 
can get it (chlorofluorocarbons are bad for the Ozone layer).


Jeff



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