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Posted by on July 29, 2005, 7:31 pm
I am looking afor a new central AC. I live in Florida so efficiency is
important. I looked at Tranes, and found that the 4 1/2 ton unit I
looked at was rated at a 14 SEER, yet the specs stated it drew 27.5
amps for the compressor, an amp or so for the compressor fan, and 7
amps for the air handler blower (full speed). Now 4 1/2 tons is 54000
BTU's per hour, and the power draw is (27.5+1+7)amps X 220V, or 7800
watts. This would seem to me to give a SEER of 6.9. This is less than
half of the stated SEER of 14. Can anyone explain this? I looked at
the ARI website and this seems to be the case for every manufacturer.
If I buy a buy a 14 SEER 54000 BTU/hour AC, I would expect it to draw
54000/14 watts, or 3850 watts. Can anyone explain this? Neither the
Trane dealer or distributor could answer this. Thank you in advance.
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Posted by SQLit on July 29, 2005, 1:03 pm
>
> I am looking afor a new central AC. I live in Florida so efficiency is
> important. I looked at Tranes, and found that the 4 1/2 ton unit I
> looked at was rated at a 14 SEER, yet the specs stated it drew 27.5
> amps for the compressor, an amp or so for the compressor fan, and 7
> amps for the air handler blower (full speed). Now 4 1/2 tons is 54000
> BTU's per hour, and the power draw is (27.5+1+7)amps X 220V, or 7800
> watts. This would seem to me to give a SEER of 6.9. This is less than
> half of the stated SEER of 14. Can anyone explain this? I looked at
> the ARI website and this seems to be the case for every manufacturer.
> If I buy a buy a 14 SEER 54000 BTU/hour AC, I would expect it to draw
> 54000/14 watts, or 3850 watts. Can anyone explain this? Neither the
> Trane dealer or distributor could answer this. Thank you in advance.
>
Depending on the unit the inside fan is probably 120v. Especially if it is a
VFD.
7 amps is pretty high for a 240v motor. My American Standard with a VFD
never drew full load amps. My American Standard 5 ton 12 seer said it
stated 28 amps, ( older model ) I never measured more than 23 amps usually
it was 19 or 20.
Also you should be using 240v not 220. Calculations are done (usually) on
nominal voltage.
Have you measured the draw?
www.advancedenergy.org/buildings/knowledge_library/heating_and_cooling/seer_
facts_bulletin.pdf
The installer is the one who makes the job. Not that your installer did a
bad job.
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Posted by Slumlord on July 29, 2005, 4:29 pm
SEER ratings are done at specific Dry bulb & Wet bulb temps for both the
exterior and interior.
Interior Temps: 80 F Dy bulb, 67 F Wet Bulb
Exterior TEmps: 82 F dry bulb, 65 F Wet bulb
High SEER system see can see a faster degradation in efficiency than
lower SEER systems as it gets hot outside. ASHRAE recommended a better
system for testing efficiency, where a perforance range is calculated
over a range of indoor and outdoor conidtions. So far, the Feds have
ignored this advice. As a result, using the SEER rating to estimate
what your operating costs will be, will not give you an answer close to
what you really get!
melbjer@hotmail.com wrote:
> I am looking afor a new central AC. I live in Florida so efficiency is
> important. I looked at Tranes, and found that the 4 1/2 ton unit I
> looked at was rated at a 14 SEER, yet the specs stated it drew 27.5
> amps for the compressor, an amp or so for the compressor fan, and 7
> amps for the air handler blower (full speed). Now 4 1/2 tons is 54000
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Posted by Slumlord on July 29, 2005, 4:33 pm
I should also mention that the quality of power coming into your home
will affect the efficiency. During the summer, the voltage going into
your home could drop as much as 5%, raising the amp draw. Also, if
there are a lot of inductive (motors) or capacitive (flourescent lights)
on the grid you draw power from, the power factor could be off. Since
simple amp meters don't read power factor, you may not be measuring what
the true power draw of your A/C system is.
melbjer@hotmail.com wrote:
> I am looking afor a new central AC. I live in Florida so efficiency is
> important. I looked at Tranes, and found that the 4 1/2 ton unit I
> looked at was rated at a 14 SEER, yet the specs stated it drew 27.5
>
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Posted by on July 29, 2005, 4:57 pm
>I should also mention that the quality of power coming into your home
>will affect the efficiency. During the summer, the voltage going into
>your home could drop as much as 5%, raising the amp draw. Also, if
>there are a lot of inductive (motors) or capacitive (flourescent lights)
>on the grid you draw power from, the power factor could be off. Since
>simple amp meters don't read power factor, you may not be measuring what
>the true power draw of your A/C system is.
This is moot, since household kWh meters only charge for real power.
Nick
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