Re: [Phys-l] Air Conditioner Sizing (was Another Try)

[Brian Whatcott <betwys1@sbcglobal.net>]

At 05:02 PM 8/26/2006, Edmiston, Mike wrote:
> ...
> I am cooling about 3000 sq ft in northwest Ohio with less than 2 tons.
> ... I am using
> window AC units ...I have four 6000-BTU units.  At 12,000 BTU per
> ton, that means I have exactly 2 tons.  However, I only run two units
> (one upstairs and one downstairs) unless the temperature gets over 85 F
> oustide.  Today it is about 90 F and quite humid, so I have all four
> running.

///

> The science building at Bluffton University just had its 28-year-old AC
> unit replaced.  A 25-ton compressor was replaced with a two-stage unit
> consisting of a 10-ton compressor and a 15-ton compressor.  For most of
> the summer we have been running the 10-ton only and continuously.  It is
> cooling fine and keeps the humidity much lower than when we ran the
> previous 25-ton that cycled on and off.  Only on a few days when the
> outside temp went above 95 F did the 15-ton stage kick in.  We're saving
> electricity and keeping drier with the two-stage unit.
>
>
> Michael D. Edmiston, Ph.D.


Here's another way of thinking about sizing air handlers.
An AC unit tends to have equation like this:
tons of ice equivalent = volume to be cooled
 times
maximum temperature drop from ambient desired.

If one can be happy with less drop from ambient, then
the tons of ice required drops, or the volume to be cooled
 can be greater.

I notice that domestic air units tend to top out at about
23 degF drop hereabouts. At 97 degrees outside,
 the house was holding 75 degrees for a while, though
 I prefer it a little cooler.
It looks like one ton gives Ed a 10 degree drop at home,
which seems respectable. But perhaps he can handle
indoor temperatures higher than 75 degrees?



Brian Whatcott    Altus OK    Eureka!