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Re: [Phys-l] cooling hints




On 2011, Aug 24, , at 20:42, James Mackey wrote:

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


The maligned conceptual text discusses this in some detail. I'm curious. Did James ask for an explanation? Afterwards I'd try using data collection and integrating to show why catch up is a small compared to the the energy lost by continuous use of the heater of chiller. Preceding this, one has a Newton's cooling law experiment -- for the more advanced one separates radiation, transmission and convection.

bc