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#127998 - 05/10/02 02:09 PM Window air conditioner  
Frank Cinker  Offline
Member
Joined: Jul 2001
Posts: 311
Pennsylvania
15,000 BTU, 115 volt air conditioner. What is the formula to convert to amps?

Frank

[This message has been edited by Frank Cinker (edited 05-11-2002).]


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#127999 - 05/10/02 04:01 PM Re: Window air conditioner  
pauluk  Offline
Member
Joined: Aug 2001
Posts: 7,520
Norfolk, England
Frank,

The conversion factor is 1kW = 3413 BTU/hr.

Thus 15,000 / 3413 = 4395 watts

Calc. current = 4395/120 = 36.625 amps.

Actual current will be higher of course, depending upon the efficiency and power fsctor of the A/C unit in question.


#128000 - 05/10/02 04:17 PM Re: Window air conditioner  
Bill Addiss  Offline
Member
Joined: Oct 2000
Posts: 3,875
NY, USA
Paul,

(That doesn't even sound close)

Bill


#128001 - 05/10/02 09:38 PM Re: Window air conditioner  
pauluk  Offline
Member
Joined: Aug 2001
Posts: 7,520
Norfolk, England
Quite right Bill, I've just looked at a catalog and seen a 1-ton (12000 BTU) A/C unit that draws 11.5 amps @ 120V. Oops!

I just took the straight watts-to-BTU/hr conversion which would be valid for HEATING, but not for A/C. We don't have much need for A/C over here, so I guess I just wasn't thinking hard enough -- Sorry folks.

According to my data, you put an EER (Energy Efficiency Rating) on your A/C units, which works out as BTU/hr (of COOLING power) divided by input wattage.

So electrical power would be BTU / EER.

Obviously the exact figure would then depend upon the EER, but from the listings I have somewhere around 9 to 10 seems to be typical for a 15,000 BTU unit. That would result in a current of around 12.5 to 14A @ 120V, plus a little for power factor.

Sound better?


[This message has been edited by pauluk (edited 05-10-2002).]


#128002 - 05/11/02 07:06 AM Re: Window air conditioner  
Frank Cinker  Offline
Member
Joined: Jul 2001
Posts: 311
Pennsylvania
Please post foumula you used to obtain amps. Just the simplified version, excluding efficiency and power factor. For example, if the only information you had on a window air conditioner was 15,000 BTU, 115 volts.
I'm aware all you have to do is look at the nameplate. I just want to learn a very basic formula to convert BTU to amps for air conditioner units.

I divided the BTUH (4395) / 3.4 to get 1292 and then divided by 115 volts to get 11.23amps. Am I even close??

[This message has been edited by Frank Cinker (edited 05-11-2002).]


#128003 - 05/11/02 10:33 AM Re: Window air conditioner  
pauluk  Offline
Member
Joined: Aug 2001
Posts: 7,520
Norfolk, England
Hmm, slightly new territory for me here; as I said we don't get involved with A/C much over here.

If the EER of the unit is not available, I would guess you would just have to resort to an estimate of a typical value to get a rough idea of the current.

I did a Google search on keywords "air condition efficiency," and came up with several links which seem to agree that around 10 is a reasonably good EER on modern A/C units.

If we plug that into the formula, it becomes (ignoring p.f.):

Amps = (BTU / 10) / voltage

That will simplify down to:

Amps = BTU / 1200 (for a 120V unit), or

Amps = BTU / 2400 (for a 240V unit)

Would any A/C experts agree with these figures?


#128004 - 05/11/02 12:59 PM Re: Window air conditioner  
Frank Cinker  Offline
Member
Joined: Jul 2001
Posts: 311
Pennsylvania
Paul,

Thank you for reply. If we stay with my original example: Window air conditioner: 15,000 BTU, 115 volts. How would you apply your formula to get amps? Also, what does EER mean? One more question....What is the average power factor for a window air conditioner?

[This message has been edited by Frank Cinker (edited 05-11-2002).]

[This message has been edited by Frank Cinker (edited 05-11-2002).]


#128005 - 05/12/02 11:11 AM Re: Window air conditioner  
pauluk  Offline
Member
Joined: Aug 2001
Posts: 7,520
Norfolk, England
I've seen EER listed as both Energy Efficiency Rating and Energy Efficiency Ratio, although they amount to the same thing.

Assuming the EER of 10, your original figures would then be:

Current = 15000 BTU / 1200 = 12.5 amps.

But keep in mind that that figure is based on my quick search showing that 10 is a reasonably good EER.

I'm not sure what the average p.f. would be on these units, although I would guess that they're capacitor-corrected to keep it as high as possible.

There must be some of you other guys with experience of these units. Anyone???


#128006 - 05/12/02 11:20 AM Re: Window air conditioner  
Frank Cinker  Offline
Member
Joined: Jul 2001
Posts: 311
Pennsylvania
Paul,

I appreciate you staying with me on this. Little by little I'll gain more knowledge on the subject. I wonder if the EER is around 10 if that indicates 100% power factor.

Frank


[This message has been edited by Frank Cinker (edited 05-12-2002).]


#128007 - 05/12/02 04:56 PM Re: Window air conditioner  
pauluk  Offline
Member
Joined: Aug 2001
Posts: 7,520
Norfolk, England
It's more knowledge for me as well. As I said, we don't have much A/C in this land of cool weather and warm beer, hence my initial goof of just converting BTUs to watts as though it was for heating.

The EER won't represent the power factor of the system, just the efficiency with which the electrical power is converted to cooling power. Some of the links I found show some super-efficient A/C units with an EER of 12 or more.

I have a couple of U.S. catalogs here with A/C units in them. I'll see if I can find any with enough data to work out the p.f.


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