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Re: [Phys-l] cooling hints



Obviously this is not true in the limit of turning it off for a long time
say a month.

It would not appear to be correct if you assume that the air conditioner has
a fixed efficiency for pumping thermal energy. Actually if you just turn up
the temperature the rate of heating is decreased as the temperature
differential between the inside and outside is decreased so the AC doesn't
have to work as hard and you save energy.

But if the AC changes efficiency then the equation is a bit different. One
would think its efficiency might go up as the inside T increases, but that
is probably a small effect. In either case an increase in efficiency at
higher T would help save energy.

This same question asked about heating plants is unequivaly that it is more
efficient to turn it off when you are out than just turning the thermostat
down. But heating technicians will often repeat the old wives tale that it
is more efficient to turn down the thermostat than to turn off the heat
totally. The main disadvantage is that you may come home to an
uncomfortable house unless the AC or heat go on a little before you arrive.
Also the changes in humidity or temperature extremes might be damaging to
some of the contents of your home.

So I would say it is probably nonsense.

Maybe they just want to sell you more energy. Or perhaps they would prefer
that everyone has their energy demand moderately spaced over a period of
time. If everyone turned off their AC when going to work and then turned it
on at 5PM the load on the electrical network would be enormous and might
necessitate brown outs or rolling black outs.

Then again they might not really know, and are just repeating an old wives
tale!!! I would be tempted to write a letter or response to the article
saying that this in not physically possible. But the article may have been
an infomercial.

John M. Clement
Houston, TX



In a recent newspaper article about energy efficiency, an
energy company
spokesperson said
"If you actually turn your air conditioner off for periods of
time, the
amount of energy it will use as it tries to "catch up" and
make the house cool
again is more than if it comes on periodically throughout the day."
Am I missing something practical here or is this statement as
wet as the
condensation from the air conditioner?