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Re: [Phys-l] cooling hints



That doesn't sound right. Refrigerators can lower the temperature from the
70s or higher to below freezing, and they work the same way an AC does.
Actually the vents in our houst put out much colder air than the temperature
we wish, so obviously it is producing a much colder temperature than a 15
degree difference. On the really hot days, the indoor temperature is more
than 20 degrees different from the outside. The waste water coming out of
the AC is quite cold. Thirty years ago I know Houston houses could be
cooled more than 15 degrees below outside ambient. Without AC Houston would
probably be abandoned.

The cooling power depends on the capacity of the AC, and it is possible to
get one that will chill your house below what would be comfortable, but
usually that is not optimal. On the Gulf Coast one wants the moisture
removal, so you want an AC that stays on for a long enough time to do this.
One that is too powerful will cool too quickly and you get a cold clammy
home.

I suspect that the 15 degree difference is what was achieved in the average
home with little insulation. I also suspect that the temperature of the
inside and outside coils is determined by the design of the AC and has only
a small dependence on the ambient temperature. As long as the outside
ambient is significantly lower than the outside coil temperature the AC
should be able to maintain a very low indoor temperature in a perfectly
insulated sealed home.

I am pretty sure that even back then you could get a greater temperature
differential if you just paid for a larger AC unit. Most repair people tend
to tell you what the manuals say regardless of whether it is correct or not.
Advertising can also be totally incorrect. For example I saw a tag on a
lamp that claimed that its 60W halogen bulb saved you energy compared to a
lamp with a conventional 60W bulb. What were they thinking? Since the 6
inch fiberglass insulation has a better R value than the 4 inch insulation
people have been told to install the 6 inch in the 4 inch space. But
squishing it just reduces the R value to the same as the 4 inch. I am sure
we all have similar common misconceptions to report.

John M. Clement
Houston, TX



In regards to a/c cooling -- may have changed a bit but many,
many years ago
when I was married to my son's father, he was an a/c repair
person for part
of his working life. He would always tell me that and a/c
can lower the
inside temp about 15 degrees and that is all. So, if it is
103 degrees out,
like we had this summer (NOT heat index, plain, ordinary
pre-meteorologists
temperature), you will be lucky to have your house cool at 88
degrees. Of
course, a lot depends on insulation, sun through the windows,
children/pets
running in and out, etc.
Holly Priestley

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