[K12OSN] electricity use

[Tim Frichtel]

I've gone through two office & server room remodeling projects where I 
worked with the engineers.  A couple of things to keep in mind - per the 
US National Electric Code, the continuous load on a 20A circuit 
shouldn't exceed 80% (16A) and you do need to allow for load surges when 
you start equipment. The engineers typically allowed for several PCs per 
circuit, so I don't understand what Dell is telling your school. 

Do you know if your room has dedicated circuits or does it share with 
other classrooms?

My experience is a typical PC usually doesn't draw as much as the power 
supply is rated at - maybe 150W during routine use. The stickers on 
equipment are conservative and allow for maxing out a PC - fast CPU, 
high-end graphics card, extra drives, memory etc.

An old PC with the hard drive, CD, floppy etc disconnected will use a 
lot less power than a "fat" PC.  For instance, an old Dell P3 I use with 
LTSP only draws 43W when running as a thin client.  Coupled with an LCD 
monitor, you are looking at roughly 90W per station.   I've had great 
success with HP's thin clients - base models ($200) work great with 
LTSP, and draw around 18W when running.

You should be able run the lab on LTSP with less power (and heat and 
noise) than you have today with 20 full PCs, even taking into account a 
decent server, UPS and network switch.

Estimate with old PC thin clients:
1 Server &  LCD monitor - _maybe_ 300W (no redundant power supply)
20 old PCs, with CD, HD etc disconnected (45 W each) with LCDs (45W ea) 
- 1800W
Network switch - less than 100W
Lab total = 2200W (18A)

Estimate with new thin clients:
1 Server & LCD monitor - _maybe_ 300W
20 thin clients (20W each) with LCDs (45W ea) - 1300W
Network switch - less than 100W
Lab Total =1700W.  (14A)

The estimates don't factor in the power needs of a UPS for your server 
or allow for anything else to be plugged in, but you get the idea.  CRT 
monitors and not having the budget for thin clients hurts the equation, 
but if the school has some money for new PCs, you can get 5+ thin 
clients for the cost of a nice new PC.

Tim


Brad Thomas wrote:
> I am a social studies teacher and I've been building a lab in my classroom
> of old, discarded computers over the last two years (I was up to 20). I
> have been using small distros like DSL (DamnSmallLinux) to make them work,
> but was planning to switch to a k12ltsp setup before the end of the year.
> However, my principal just sent an e-mail last week instructing me to
> remove all but 6 of the computers from my room implying that they were
> using too much electricity. I just got back from a school planning council
> meeting where she and an assistant principal said that they called Dell
> (we buy all our new fat machines from Dell) and Dell said there should
> only be one computer per 20 amp circuit (which translates into one per
> room I think). As far as I can tell (using a Watts Up meter) one
> computer-and-monitor use a little more than 1 amp of power, so I don't get
> this. Can anyone out there give me some guidelines they go by? Or steer me
> to a good site? How much planning goes into ensuring proper electrical
> flow into your k12ltsp labs?
>
> Brad
>
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