RE: DATACENTER: Datacenter HVAC requirements

[Deepak Jain <deepak@ai.net>]

20A or 30A (whatever you are breaker'ing for) is an outside limit per
rack. In my understanding, 1 watt ~= 3.4 BTU/hr is iff your convert 100%
of the line energy to heat (impossible). Therefore, if you take your
complete breakered amperage, multiply by voltage, then again by 3.5,
adding a generous margin for the actual square footage and absorbing heat
from people and the outside (doors, windows, etc) and the amount genreated
by lights (if they aren't on the same panel).  You should have an outside
number on the maximum heat generation. 

However, you can subtract things like the A/C's power as in many cases, 
the BTU output is net the heat generated by the equipment in the premise. 

Simple rule of physics is that you can't generate more heat than you are 
putting in (as electrical energy).

-Deepak.

On Mon, 14 Jun 1999, Gregory Trubetskoy wrote:

> 
> I would not recommend relying on rules of thumb such as 20A per rack. The
> equipment out there is getting denser and denser, and with those 2U server
> chassis that everyone makes these days, I can see a rack drawing over 30A.
> Don't underestimate a loaded cisco 7505, they too can draw a lot of power
> when loaded.
> 
> A more accurate estimate can be made by actually looking at what equipment
> you'll be placing there. If you underestimate, upgrading later on is not
> always an option and will certainly cost more than doing it right from the
> start. 
> 
> Grisha
> 
> On Mon, 14 Jun 1999, Metcalf, Andrew (ATL) wrote:
> 
> >  We have about total 15 full racks of equipment (we are at about 15Kva (out
> > of 70) on the UPS now) and a 20 ton cooling unit and everything is fine...I
> > have about 20 more racks to fill...looking at the MRTG of the temp sensor
> > there is no fluxuation (temp or humidity) and it stays in the temp range I
> > told it too....so i don't think i'm even close to stressing it.
> > I don't have any formulas...but thats whats happening in the data center
> > here.
> > 
> > andrew
> > 
> > -----Original Message-----
> > From: Robert Szarka
> > To: datacenter@shorty.com
> > Sent: 6/14/99 10:47 PM
> > Subject: Re: DATACENTER: Datacenter HVAC requirements
> > 
> > At 07:36 PM 6/14/99 , Mark Smith wrote:
> > >
> > >Ok, so if I look in my cool little master converter program it tells me
> > >that 1 watt = 3.4120962 BTU/hr. So my questions is how much cooling do
> > 
> > Actually, the rule of thumb I've seen is 1 watt = 3.5-3.7 BTU/hr.
> > 
> > >I need for my datacenter? Is it as simple as:
> > >
> > ># racks * 20 amps a rack * 3.4120962 / 12,000 (BTUs in a ton) = tons of
> > >HVAC required?
> > 
> > But an amp isn't a watt!  It's been a couple of years, but I think since
> > Ohm's Law gives P = I x E (power = current x voltage), and assuming 120
> > volts, you get something on the order of 2.4 kva if the circuit were
> > fully
> > loaded.  So if your hypothetical rack on a 20 amp circuit were
> > generating
> > 2.2 kva you'd need something on the order of .7 tons of cooling per
> > rack.
> > Now, I am definitely *not* the HVAC guy (or the electrical engineer)
> > here,
> > so that could be way off, but that's how it looks to me.
> > 
> > Of course, a quick peek says my server room is sucking up only a little
> > over a kilowatt right now, so if you have more routers than hard drives
> > in
> > that rack, I'd guess you'd be overbuying cooling quite a bit.  Given the
> > weather, that doesn't seem like a bad thing, but...  :)
> > 
> > 
> > -- 
> > 
> > Robert Szarka
> > Managing Partner, Operations
> > DownCity, LLC
> > +1 860 823 3000
> > 
> 
>