meirman wrote:

In alt.home.repair on Sat, 12 Jul 2003 18:47:57 -0400 "HeatMan"
posted:


"Joseph Meehan" wrote in message
. ..


Because it is more than 78º in side and to keep it there it needs to
run. You could open up windows and run a fan to get it below 78º but that
would let in so much moisture, the A/C would run longer to get rid of that
extra moisture than it now runs to keep it down to 78º.


Actually, that's not completely correct.

If the homeowner has a combination thermostat/humidistat that will turn on
the A/C to lower humidity, you make an excellent point. In other words,
most current Tstats have no way to measure the %RH in the house.

Otherwise, the Tstat is just reading the heat level in the house.



Yes, but I think it is harder, that is, takes longer, takes the
removal of more heat, to cool humid air than to cool dry air. I can't
explain this well -- the boundary between water and ice might be more
explainable -- but somewhere in the cooling process one has to cool
the water vapor until it condenses into water itself again. Obviously
it's not 212 degrees Fahrenheit in the house, but there is still some
temperature where the humidity condenses into water, and it takes a
lot of cooling to do that.

One would think one could just cool the air and leave the humidity
high, but the laws of physics and the AC won't let that happen. The
maximum amount of water in the air is lower when the air is cooler.
So when the air gets cooler, some water has to condense out. But in
the process of cooling that water vapor from X degrees as a gas to the
same temperature, X degrees as a liquid, the gas gives up a lot of
heat, heat that has to be removed by the AC.

The one big question this leaves is: Is the relative humidity inside a
a room with AC always 100% (or near there). I don't understand why it
wouldn't be, but by personal experience I don't think it is that high.
It doesn't seem humid but maybe that is just because it is cool.
Does anyone know I think the humidistat means that the AC will run even when it is
below the set temperature, until the humidity is at the desired level.
But iiuc, it does this by cooling the air some more and driving out
the water. Maybe there is some arrangement of the cooling coils that
reduces humidity more efficiently than it lowers temp. Does anyone
know? Meirman


It's time to get some straight scoop on latent heat removal. To save NG
space read pages. - Darrell

--
Air Conditioning - Latent Heat Removal -
http://www.udarrell.com/air-conditio...tent-heat.html