[Beowulf] Re: "hobbyists"

Robert G. Brown rgb at phy.duke.edu
Wed Jun 25 13:09:28 EDT 2008


On Wed, 25 Jun 2008, Vincent Diepeveen wrote:

> When i just walked previous week into a shop and my sister was interested in 
> a new washing machine,
> i pointed her to the fact that the thing she was interested in, was eating 
> 3.8 kW, versus the 100 euro more expensive
> thing next to it was eating 1.14 kW. It is something that only very few will 
> notice.

Hey V.

But that's not the important question; only a factor to it.  The
important question is how much energy total is used, not the rate used,
and that may depend on lots of things.  If you have to wash your clothes
twice (or several times as long) to get them as clean (lower power means
lower SOMETHING -- less agitation, less heating of the water, smaller
capacity so you have to run more loads) then you have to factor in power
times TIME, really the system time, your own time, and the energy and
monetary cost of doubling the wear on your clothes.

> It is easy to cheaply produce equipment that eats more power than equipment 
> of competitors, that is the fundamental problem.

And it is equally easy to produce an "energy saving" product that saves
energy by not working as well, or at all.  I'm not really arguing, by
the way -- only pointing out that you should look beyond JUST the energy
RATE of draw and make sure that the product will actually perform just
as well and still save total energy and do what you need it to do.  It
isn't always easy to do that, and it goes beyond just looking at the
power consumption rate.  Lower power could translate into "wearing
slightly dirty clothes all the time" or it could translate into "getting
a load that is just as large of just as many clothes just as clean --
but saving 2.5 KW every hour you use it."

Then to REALLY do the CBA -- once you've established that it is all
things being equal comparison -- you have to count the expected number
of hours of operation over the duty cycle of the machine -- if you use
it (say) three hours a week, that's around 150 hours a year, times ten
years is 1500 hours.  At a generous dime a KW-hour, that's a savings of
maybe 350 Euros over ten years at a cost of an extra $100 now.  Not bad,
but not spectacular, either.  If you use it more than 3 hours a week
(and it draws the 2.5+ KW power differential for all of that time, which
I doubt unless it is heating the water, in which case you have a variety
of alternative solutions because heating water to a given temperature
can't be done more or less efficiently, really) then you might save
more.

To put it another way, if it really is talking about PEAK draw, not
CONTINUOUS draw -- a 3.5 KW washer couldn't even be plugged in over here
and 3.5 KW is a huge draw for any appliance that doesn't heat water --
you might not save anything at all beyond the fact that you don't need a
special circuit to run it on.

If it IS heating water, then you need to be very careful.  It takes a
certain number of joules to heat water, period.  Most washers let you
choose to run a cold water wash, or select any degree of warmth.  In the
US they tend to get hot water from a hot water heater that delivers it
for the whole house (so they only need a few hundred watts to run,
enough to run the washer motor and a pump).

If there is a power differential but they heat the same amount of water
to the same temperature, they use the same amount of energy to do it
(within a hair) period.  They probably use very similar -- and much
lower -- amounts of power to do the actual washing, or use higher power
for spins and so on for brief periods of time.  In this case there is
almost certainly NO marginal cost advantage in the lower power unit
except the need for cheaper receptacles to plug it into, and there might
even be a total energy loss.  Yet by putting a big notice on the
machine, they can fool people into spending an extra hundred Euros.  I'd
ask lots of questions of the salespeople and fully understand the energy
budget of the machine, not just the peak draw, before concluding that it
is more or less "green".

So this sort of CBA is a very good idea, but it has to be carefully
done.  It's miles per gallon that matters, not gallons per minute, so to
speak.  Amount of work done per delivered/purchased joule, not number of
joules per second drawn to do possibly differential amounts of work with
possibly differential quality in possibly differential amounts of time.

    rgb

--

>
> Vincent - speaking for himself
>
> On Jun 25, 2008, at 8:43 AM, Jon Aquilina wrote:
>
>> how much does a sugar glass window cost now that sugar and other things are 
>> being used for bio fuels?
>> 
>> On Wed, Jun 25, 2008 at 12:20 AM, Mark Hahn <hahn at mcmaster.ca> wrote:
>> 
>> More specifically for HPC, linux seems designed for the desktop, and
>> for small memory machines.
>> 
>> the only justice I can see in that is that there hasn't been all that much 
>> effort to get bigpages widely/easily used.  in particular, I don't
>> see that scheduler or general memory-management issues in linux are
>> particularly biased for desktop or against HPC.
>> 
>> 
>> That's funny, because I've heard people get scared that it was the complete
>> opposite. That Linux was driven by Big Iron, and that no one cared about
>> the "little desktop guy" (Con Kolivas is an interesting history example).
>> 
>> Con didn't play the game right - you have to have the right combination of 
>> social engineering (especially timing and proactive response) and good tech
>> kungfoo.  kernel people are biased towards a certain aesthetic that doesn't
>> punish big-picture redesigns from scratch, but _does_ punish solutions in 
>> search of a problem.
>> 
>> so the question is, if you had a magic wand, what would you change in the 
>> kernel (or perhaps libc or other support libs, etc)?  most of the things I 
>> can think of are not clear-cut.  I'd like to be able to give better info 
>> from perf counters to our users (but I don't think Linux is really in the 
>> way).  I suspect we lose some performance due to jitter
>> injected by the OS (and/or our own monitoring) and would like to improve,
>> but again, it's hard to blame Linux.  I'd love to have better options for 
>> cluster-aware filesystems.  kernel-assisted network shared memory?
>> 
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>> 
>> -- 
>> Jonathan Aquilina
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-- 
Robert G. Brown                            Phone(cell): 1-919-280-8443
Duke University Physics Dept, Box 90305
Durham, N.C. 27708-0305
Web: http://www.phy.duke.edu/~rgb
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