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seer rating doesn't match power draw melbjer 07-29-2005
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Posted by on July 31, 2005, 4:01 am



>...the convention of saying BTU when BTUH is meant has set in and will be
>difficult to purge from the language.

It's Btu/h, ie Btus per hour. BTUH would be Btus times time...

Should we discard our ACs when they run out of Btus? :-)

Nick



Radiant Heat 468x60
Posted by ~^Johnny^~ on July 31, 2005, 1:39 am


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On 31 Jul 2005 04:01:14 -0400, nicksanspam@ece.villanova.edu wrote:

>It's Btu/h, ie Btus per hour.

Yes.

>BTUH would be Btus times time...

Well... a BTU is a BTU per hour for an hour,
making it a BTU per hour hour.
So, what you are saying is a BTUH is a btu per hour hour hour.
Since "per hour" and "times hour" cancel out,
a BTU per hour hour hour equals a BTU per hour.
Therefore, BTU/hr == BTUH. :-)


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--
-john
wide-open at throttle dot info


Posted by RP on August 1, 2005, 12:49 am




nicksanspam@ece.villanova.edu wrote:

>
>
>>...the convention of saying BTU when BTUH is meant has set in and will be
>>difficult to purge from the language.
>
> It's Btu/h, ie Btus per hour. BTUH would be Btus times time...

In a mathematical formula yes, but as an abbreviation of language BTUH
is read btu per hour :) It's yet another case of dumb-ass convention ;)

hvacrmedic


>
> Should we discard our ACs when they run out of Btus? :-)
>
> Nick
>



Posted by Rick Matthews on July 30, 2005, 10:43 am


Carolina Breeze HVAC wrote on 7/30/2005 7:24 AM:
>
> Reduces load for starters.
>
> Amps mean nothing of great importance here..you can have a 16SEER unit
> pulling 50 amps and its still 16SEER.
>
> Bottom line, for every watt used, how many BTUs are being removed?

Exactly.

Elaborating on this answer, for lights, power is watts times
amps. This is still true *instantaneously* for everything,
but for motors the current and voltage or not in phase.
These means that part of each cycle voltage and current are of the
same sign, resulting in positive power consumption, just like lights.

But for the rest of the cycle,they are of opposite sign, so that
the power is negative. In other words, the motor is actually returning
power to the power company for this portion of the cycle.

You only care about the average power consumed over an entire
cycle, which for a motor running at full speed is considerably
less than the rms current times rms voltage.

--
Rick Matthews matthews@wfu.edu
Department of Physics http://www.wfu.edu/~matthews
Wake Forest University 336-758-5340 (Voice)
Winston-Salem, NC 27109-7507 336-758-6142 (FAX)
USA


Posted by Pop on July 30, 2005, 3:38 pm



> On Fri, 29 Jul 2005 19:31:43 GMT, 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
>>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.
>>
>
>
> You are wrong to assume that amps are indirectly
> proportional to
> SEER.

That's correct: The SEER is calculated to include the
phase shifts etc. introduced by the loads, which is why
direct calculations such as the OP used won't wash.
In addition, nameplates & labelling isn't always
accurate. It's often stated to be even higher than the
actual draw, just to account for the possible
variations in the production of multiple units. So
they use a max number on the plates and for the saftey
agencies. Plate numbers are only for sizing wiring to
the unit.
If it has a SEER rating, and a safety label (UL,
CSA, CE, et al), which is a requirement, then the
numbers are correct.

HTH

Pop




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