RE: DATACENTER: AC and colo sizing question.

[Ken Woods <kwoods@verio.net>]

All further proof that you don't give a shit about return air temp.

You should keep the temp under the floor constant, and control above floor
(ie, in the space) temp with perf placement.




On Wed, 16 Feb 2000, Christopher E. Brown wrote:

> On 16 Feb 2000, Sean Donelan wrote:
> 
> > On Mon, 14 February 2000, "Christopher E. Brown" wrote:
> > > 
> > > I would say 65F rather than 75F, with an absmax of 70F.
> > 
> > Most modern electronic equipment can operate in a "nominal"
> > office environment.  Unfortunately, you rarely find this
> > environment outside of textbooks.  There is also telco/NEBS
> > equipment which can handle greater environmental extremes, and
> > computer room equipment which can handle less environmental
> > extremes.  But if you have one of the later, you usually know
> > the specific requirements you have to meet.
> 
> 	There is this.  I will admit that my hardware (Biped V1.5)
> finds anything over 70F troublesome, and 65F preferred.
> 
> > I've found 72F (+/- 3F) will satisify nearly 100% of electronic
> > equipment commonly found in computer rooms.  Even the most
> > temperamental pieces of electronic equipment have a maximum
> > recommended temperature no lower than 77F (25C).  Note: all
> > measurements taken at the equipment air inlet, not at the CRAC.
> 
> 	Yes, I tend to assume given a usual lack of control over when
> gets stuffed into racks not under my direct control that input air for
> at least some of the devices will be 5 - 10 F over room temp (the
> other reason for a 65F base point).
> 
> > > The equipment is designed to operate with a max intake air
> > > temp of X with Y CFM flow.  You must maintain an input air temp well
> > > below the devices rated max, and prevent obstructions to the airflow.
> > > 
> > > This means paying attention to where devices exhaust to, and
> > > keeping said exhaust from the intake for other devices.
> > 
> > Yep, a rack is its own mini-climate.  The temperature can vary tens of
> > degrees from the bottom to the top.  Injecting super-cooled air into
> > the bottom, hoping it won't be heated too much by the time it reaches
> > the top isn't the best method.  But rack design seems to be a lost
> > art.  In the "old days" (i.e. 10 years ago) there were specialists at
> > all the mini and mainframe companies which took great care planning
> > cabinet layouts.  In today's world of Do-It-Yourself server assembly,
> > the goal seems to be cram as many ascend maxes into a 84" rack as
> > possible with no thought.
> 
> 
> 	Yep, it would be a wonderful world if this all was planned
> out, all devices with matching air intakes/exhausts in a rack with air
> channels designed for it, and a nice sub floor chilled air supply.
> Unfort for me I have never seen this happen with todays DIY setups.
> Always end up with some silly thing without enough fans picking up
> 80F air and not being happy.  One of the fun issues is PC based
> servers.  Great, you can get alot of bang for the buck, this does not
> mean you can take generic low end hardware, slap it together without
> planning and expect to be happy (this seems to be the common case
> though).  No in chassis air flow or volume planning, and you end up
> with alot of systems that go TU if at full load and the intake temp
> passes 80F. :(
> 
> ---
> As folks might have suspected, not much survives except roaches, 
> and they don't carry large enough packets fast enough...
>         --About the Internet and nuclear war.
> 
> 

-- 
Ken Woods
kwoods@verio.net