Watts to Amps calculation

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Old 09-17-07, 10:47 AM
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Watts to Amps calculation

I'm looking at putting a window type ac unit in an insulated pole barn. For it's size I need somewhere between 12000-15000 btu's.

In preparing for the electrical needs I converted 15000 btu's to watts (4393) and then converted watts to Amps and came up with 36.6 Amps at 120 volts. Even a 10000 btu unit computes to over 24 Amps at 120VAC.

In looking at some advertised window ac units, many of these from 10000 and up to 15000 btu state that they can run on a standard 115 volt house circuit(I assume plug in). What assumptions in my calculations are incorrect?
 
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Old 09-17-07, 10:52 AM
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Look for a 240 volt unit. it will run better.

Look at the unit. Each unit will tell you what circuit size it needs.
 
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Old 09-17-07, 11:00 AM
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Originally Posted by racraft View Post
Look for a 240 volt unit. it will run better.

I understand this.

Look at the unit. Each unit will tell you what circuit size it needs.
I'm just trying to understand how some of these larger sized units can run on a 120VAC 20 Amp circuit. Based on the conversion from btu's to watts to amps it doesn't appear possible.
 
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Old 09-17-07, 11:21 AM
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Actually a 10,000 BTU 120v AC runs at 7-8 amps so I think you need to recheck your conversion factor. I'm guessing you are using a factor for direct conversion to heat which is not the same as an AC unit which is actually a pump that just moves heat from one point to another.

The actual power used is what it takes to run the compressor that moves the heat outside and the fan that moves air over the transfer coils.
 
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Old 09-17-07, 11:28 AM
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Originally Posted by ray2047 View Post
I'm guessing you are using a factor for direct conversion to heat which is not the same as an AC unit which is actually a pump that just moves heat from one point to another.

The actual power used is what it takes to run the compressor that moves the heat outside and the fan that moves air over the transfer coils.
That would make sense and I'm sure that is what I was doing. So obviously you can't make electrical assumptions based on the btu capacity of the ac unit which is what I was doing.

Thanks
 
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Old 09-17-07, 05:35 PM
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You are using a conversion factor of 3400 watts per 1000 BTU. This works when trying to estimate the BTU heating value of ELECTRIC HEAT. It is not a proper estimation of the ELECTRIC POWER used to achieve 1000 BTU of cooling.

You can easily find a 10,000 BTU air conditioner running on 120 volts, less than 10 amps.
 
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