JoeSpareBedroom wrote:
"PipeDown" wrote in message
ink.net...

"JimL" wrote in message
...
On Tue, 25 Jul 2006 16:48:44 GMT, "JoeSpareBedroom"
wrote:

Just after I moved into my (used) home, I had the AC unit cleaned &
checked
over by a company I've been happy with for 22 years. It got a clean bill
of
health. This was in September, though, so there was no really good way to
watch it do its thing for any length of time. I'm finding that on a very
hot
day (92 outside today), the system runs almost constantly to keep the
house
at 76. If I set it at 77, it cycles on for an hour, off for two, and the
house is comfortable. I don't NEED that extra degree, but I'm still
curious:
For a given house, and a particular AC unit, is there usually a point
where
it just won't do more? Or, does this mean that the previous owners didn't
have the right unit installed?

By the way, the attic is vented & insulated perfectly.

Sound like your system is designed perfectly.

The downside is that it can't quite maintain on the hottest days.

The upside is that it keeps the house dry and comfortable with
minimum energy usage.




I agree with the others that it is probably properly designed for a little
less performance than you would like on the very hottest days. You can
probably squeeze more out of it by improving insulation or shading high
heat gain areas of the house. Basically the same things you do to save
heat.

Shading the A/C unit helps, putting silver mylar (emergency blankets from
the camping store) in the windows to reflect sunlight are a couple
inexpensive things you can do quickly and are reversable if they also turn
out to be cosmetically undesireable.

Fortunately, the AC unit's in the shade for the entire day after about 10:00
AM. I've never understood people who say this isn't a factor.


I agree with Edwin that it sounds like something isn't right. The same
system running under conditons where it can maintain 77 with 1 hour on,
2 hours off, shouldn't go to running continuously when it's set to 76.
But on the other hand, for a system to maintain 77 with it 92 outside
and only run 1/3 of the time sounds like the system at that point must
be running OK, as it's not much of a duty cycle.