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air conditioner electricity useage


J Jensen

Jan 1, 1970
I have written below some questions that I posted yesterday to, sci.physics, and sci.engr.heat-vent-ac
(name of the thread is "more fun with air conditioning" if you care)

#3 and #4 are probably the only ones relevant to this group, but I thought
I might as well cut and paste the whole list:


In regards to the recent posting I saw about running the a/c or opening the
windows, I would like to list several statements that people have made to
me about air conditioning. The location is Texas, where the temperature
is about 75 F at night and 100 F at the hottest part of the day.

1. Keeping the a/c cooling the house all day uses less electricity than
turning it off and then back on in the evening or when you return from
a vacation.

2. Running the a/c a few degrees colder at night cools the big cement slab
that the house is built on, and thus saves electricity during the day
(the a/c is set back to normal living temperature during the day).

2b. If the temperature inside the house reaches 78 F at 10 AM on both days
with the a/c set colder the previous night, and also when it was just
set normally the previous night, then that proves setting it colder made
no difference.

3. The a/c uses less current at night ( you measure it with an ammeter as
it is running ).

4. The a/c uses less current if you spray the outside unit with the garden
hose and then measure it with the ammeter.

5. Shading the outside unit (compressor and condenser) does not reduce
electricity costs [Assume shade does not block air flow].

6. If you have high ceilings and ceiling fans, it is more energy efficient
to leave the fans running at low speed all the time to pull down hot air
and get it to circulate through the a/c system.

7. It isn't worthwhile to check on the amount of Freon (or whatever) that is
in the system -- all that matters is measuring the temperature of the
cold air coming out (say 62 F) and the outside temperature or maybe the
attic temperature.