Re: [Phys-l] cooling hints

[James Mackey <jmackey@harding.edu>]

The student argument was usually this: Since the unit had to run at full
power longer when the system was totally off than when the level was simply
reduced (which is true) it must use more total energy over the total cycle.
This was is opposition to the fact that the power-time curves showed less
total energy used.  However this was only one of numerous spurious
viewpoints about energy production and consumption that my students
expressed during the class.  It was an interesting experience to teach this
general education class from a physicist's perspective.
James Mackey

On Wed, Aug 24, 2011 at 11:23 PM, John Clement <clement@hal-pc.org> wrote:

> The student misconception probably comes from some concept they alread have
> and are misapplying.  It might be instructive to try to figure out what
> that
> concept might be.  At this moment I can not think of one.
>
> John M. Clement
> Bellaire, TX
>
> > Years ago, during 70s energy crisis (la plus sa change, la
> > meme la chose!) I
> > did a simulation in lab with a variac and a homemade AC box that was
> > connected to a simple immersion heater placed in a an
> > insulated beaker and
> > an uninsulated beaker.  Part of the lab was to compare energy
> > consumption
> > between complete AC turn off and reducing the set point
> > temperature.  A
> > complete cycle was run to simulate a constant AC setting, a
> > temp reduction
> > setting and a complete AC off by starting all runs at a fixed
> > temperature
> > and running through the 3 cycles for fixed times and then
> > returning to the
> > initial temperature.  Invariably, minimum energy consumption for the
> > complete cycle was lowest with the  complete turn off cycle.
> > Probably not
> > terribly applicable to today's units, but students found it very
> > surprising.  Most students believed you used more energy to
> > "catch up" if
> > you turned off the heater.
> > James Mackey
> >
> > On Wed, Aug 24, 2011 at 3:31 PM, John Clement
> > <clement@hal-pc.org> wrote:
> >
> > > I know someone who was working for the Army and in the
> > winter they used to
> > > open the windows to combat the overheating of their work
> > space.  But during
> > > one year when there was a jump in energy prices the Army
> > sealed the windows
> > > shut to prevent this.  Why they didn't just turn down the heat is an
> > > unsolved mystery.  So the employees found they could have comfort by
> > > turning
> > > on the AC.
> > >
> > > John M. Clement
> > > Houston, TX
> > >
> > > > Ah! Bitten by the "Law" of Unintended Consequences.
> > >
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