Our home is in the desert, where we cool about 9 months of
the year. When we bought the place, it had two A/C split
systems- a 5 ton and a 3 ton. There were no labels, but a
friend who is familiar with the subdivision and builder told
me that they were built-up no-name units with a SEER or <10
and no TXV. Our electric bill last year for this time of
year was >$500 and the temps were about like this year.
With that in mind, I had a good, reputable A/C company bid
on installing SEER 13 units with TXV's. The price was just
over $9k, installed.
Our home is an "open" design with a second story opening out
to a loft area. It is impossible to keep the cool air
upstairs from flowing over the railing to the downstairs.
Strangely (to me) the 3 ton unit serviced the upstairs and
the 5 ton the downstairs, which is just 25% larger in area.
The A/C company did calculations and measurements, and
told me that a 2-1/2 ton would be just fine for upstairs and
that we did need a 5-ton for the lower level, so I agreed.
The installation was done about two months ago and I was
pleased with the quality of the workmanship I saw. They
even returned on a very hot day to check the Freon levels.
Now for the strange part: The downstairs unit seldom runs
at all. This is what I would expect with the cooled
upstairs air flowing down over the railing. Both intakes
are upstairs- the one for the downstairs is in the ceiling
right over the railing, and the upstairs one is in the
middle of an interior hallway. Our electric bill for the
first really hot month was $250, which naturally includes
all lighting and about 10 hours a day on our pool's pump.
That places it at about $250 less than last year.
The upstairs 2-1/2 ton unit runs about 75% of the time on a
110f day and the upstairs is more comfortable than it was
last year. The downstairs is equally comfortable, which is
a change from last year as well. I am extremely happy with
the results of the switch, but now wonder if there was a
miscalculation on needing the 5-ton unit for the downstairs.
Without knowing the math, from what I've seen so far, a
far smaller unit would probably work just as well, if not
better, because the 5-ton unit goes sometimes 1-2 days
without even running. . . and then runs for under 10 minutes
before switching off.
Maybe, but it is not possible to say from here. Someone really should
have done the numbers and calculations to determine the size needed.
You may want to consider that if the second floor unit fails the other
one should be able to keep you alive until the upstairs unit is repaired, so
there is at least that plus.
I would have thought you would install atleast a 14 seer or greater,
especially cooling 9 months out of the year. I think the 13 and under units
are not being made anymore and you are getting the end run units. You did
not mention how big the house is or when it was built or the insulating
material and construction. A company should be able to do the calculations
for your house and recommend the correct units. As you are in teh desert I
would guess the humidity is not worth worring about as it is probably low.
In the area I live (North Carolina) the units need to be sized to run alot
to take the humidity out of the air in the summer. It will feel much cooler
with a lower humidity than it would with a high humidity.
Most definitely they run at a lower cost than Refrigerated air. However
they do use a lot more water per year which in the desert, can be a real
scarcity. As well, I would not say they work "REALLY" well. They work
but ultimately I have found with mine, the temp will only come down around
15 degrees which makes for a pretty darned hot house at 105 degrees plus.
Humidity plays the biggest role in whether they work well so after a rain,
they don't work worth a darn.
I think 13 SEER are still being manufactured. As I understand it from 3
A/C contractor's, they are still selling off the 10 and 12 Seer units and 13
SEER are the lowest versions still being made. For me a 13 SEER is
probably the best I should go with as we cool for perhaps 4 months of the
year and even then, only during the day.
Yep, you are correct. The 13 is the lowest rating still allowed to be made.
For you that may be the best for the cost vrs the payback. For the fellow
cooling for 9 months and in a very hot area I would think the payback for a
higher seer unit would be much beter.
The cold air is heavier and always flows to the lower levels. By far the
largest heatload is on the top floor and that is where the larger of the
two units should be.
This is merely speculative: I would probably have put a 3-ton system
upstairs and a 2 or 2.5-ton equipped system downstairs depending on how
one prorates the heatloads of the various areas. - udarrell - Darrell
Air Conditioning\'s Affordable Path to the "Human Comfort Zone Goal"
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