On Wednesday, July 19, 2006 7:56:34 AM UTC-4, Robert Gammon wrote:
CJT wrote:
JimL wrote:

On Mon, 17 Jul 2006 22:10:51 GMT, CJT wrote:


JimL wrote:


On 16 Jul 2006 22:13:23 -0700, "glynndaddy"
wrote:



Is there a general rule-of-thumb for how long an air conditioner
should
run and how long it should stay off? I realize this probably depends
on a variety of variables, but is there a rule-of-thumb. I've
searched
quite a bit and can not seem to find an answer.

If it helps, my house is 1 story, 2400 sq ft. I have the thermostat
set at 78. It is 85 degrees outside, humidy 72%.

Right now, my a/c stays on for 8 - 10 minutes and goes off for 7 - 9
minutes.

Thanks for your help.


yeah, what darrel said plus, my thermastat has a 1 or 2 degree
differential setting. The 2 setting makes it run longer between
cycles.

This time of year, in the hottest part of the day, a well designed
system should be running just about all the time.



No matter how hot it is, it can get hotter. I would say a well
designed
system should be running _most_ of the time; you never want to run out
of reserve. If it's at a 50-60% duty cycle, it'll be effective
removing
the humidity.


No,No. You DO want to run out of reserve. A well designed
system should
fall behind on the hottest day of the decade. It won't be able to
keep up. Your thermostat will be set at 78 but the temp will creep up
to 80, 81, 82...... etc.


With global warming, the next summer it'll be 90, 91, 92 ...

I know from BITTER experience that you do NOT want a AC system that runs
from 10:00am to 10:00pm. Power bill DOUBLES. House is livable, but
uncomfortable, especially when guests are over.

50% duty cycle, but no more than once an hour, certainly no more than
once every 30 minutes. Any faster cycling than this is dangerous for
the compressor.

Says who? If an AC cycling more than once every 30 mins
was "dangerous", there would be a lot of broken AC's out there.




A house that is 'adequately' plugged against air leaks, and has
'adequate' insulation should not have a duty cycle of greater than 50%
and really should have a duty cycle of under 25%.

Really? Even on one of the hottest days of the year?


Air leak plugs are
the new hot button, now that most new homes have at least R38 in the
ceiling and R24 in the walls, Course if we do manage to plug those
uncontrolled air leaks, then the house accumulates odors (cooking, body
odor - human and pets, solvents, cleaning fluids, paint, plastics......)
and we must then install a controlled ventilator.