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Re: [Phys-l] cooling hints



One of the things which seems to be missing in the experiment is the presence of other masses which absorb and release thermal energy (like pieces of furniture, carpet, etc.) It would be interesting for you to add a block of wood and a rock and maybe a piece of metal to the beakers and run the experiment. Homes and office buildings are not empty boxes, but contain masses which absorb and release non-instantaneously and at different rates. If you are trying to cool a house with lots of furniture, you have to cool the furniture as well as the air. This fact might contribute, sub-consciously, to the student's perception of which cycle is better.

Bill Nettles

-----Original Message-----
From: phys-l-bounces@carnot.physics.buffalo.edu [mailto:phys-l-
bounces@carnot.physics.buffalo.edu] On Behalf Of James Mackey
Sent: Wednesday, August 24, 2011 10:42 PM
To: Forum for Physics Educators
Subject: Re: [Phys-l] cooling hints

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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Forum for Physics Educators
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_______________________________________________
Forum for Physics Educators
Phys-l@carnot.physics.buffalo.edu
https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l