J Jensen wrote:
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.

Maybe, it really depends on many many factors. It would be best to
measure the specific application.


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).

See above, it might.


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.

Big if. If it does it really means your measurements/test is not valid.
College Physics 101 will tell you that if your test is accurate and all
factors are considered, there must be a difference, even if it is small.
Soft of the butterfly effect.


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

I believe that is generally true, assuming it is cooler at night.


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

Same as above, but you may end up damaging your condenser unit.


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

This is an example of inadequate measurement. There is a difference but
it is so small that it is difficult to measure. See 2b.


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.

Only if it is you goal to cool the ceiling.


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.

Worthwhile for what?


--Jeff

--
Joseph E. Meehan

26 + 6 = 1 It's Irish Math