Dave Lyon wrote:
In your case, your current AC units are spending a fair amount of time
and energy ($$) pulling water OUT of the air.


Are you saying that the act of drawing the moisture out of the air uses more
energy? I was under the assumption that dehumidifying the air was just a
nice byproduct of running your AC unit.

Taking the water out of the air costs cost 540 BTU's per pound, same as
the heat needed to change water to vapor. So, it takes energy to squeeze
the water out. The reason the AC unit pulls the water out is that once
the coil temp gets down to the dewpoint temp, all the "cold" below that
temp goes into dropping the dewpoint. So if the coil temp could be as
low as 38 degrees and the dewpoint is say 60 degrees, your ouput air
will never get below 60 degrees until you pull some moisture out.



If I understand what you are saying, a room at 90 deg will be cooled quicker
and easier by an AC unit if the humidity in that room is low than it would
if the humidity was high?

Exactly right. A 1 ton (12kbtu/h) AC that puts out a gallon of water per
hour is spending 4320 (ie (8*540 )or 1/3 of the cooling capaity to pull
water out. Only 2/3rds left to cool.

Another factoid for your luncheon enjoyment: Your comfort level is much
more a factor of the dewpoint than the relative humidity. It really
comes down to how effective your sweat function is working. At 10F or
20f dewpoint (desert air), any sweat is immediatly evaporated. At 70F
dewpoint, the whole sweat thing doesn't work well (difference between
98F body temp and the dewpoint). Most people feel dewpoint in the 60's
to be "fairly humid" and starting to get uncomfortable. 50's is "nice",
40's is "dry"

What all that says is that pulling the dewpoint down WITHOUT changing
the temp will FEEL cooler. So keep the door closed!!!

Cheers.