wattage

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j rae

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would a220v A.C. unit use the same amount of wattage as a 120v unit since
P=IE and wouldn't the 220v unit use 1/2 the amps????
 
Yes. VA & watts are the same. VA = volts x amps. 230 V amps will be 1/2 115V amps.

The 230 volt unit might be a little more efficient (1%) but not enough to make a big difference.
 
Not necessarily. I can have a 120 volt unit rated for 1 BTU, or for 2 BTU, or for 5 BTU, or for 10 BTU (I am making these numbers up). The point is that the power rating for any given unit is whatever the manufacturer wants to try to sell.

Now if you did have two units with the same power rating, and one was 120 volt and the other 240 volt, then the first will draw about double the current as the second. You are right about that part, except that there will be small differences in efficiency and losses.
 
rcwilson said:
Yes. VA & watts are the same.
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Watts and VA can be broken down into the same fundamental units of measure, kilogram-meter squared per second cubed, but they are not the same thing. In a resistive load, their numerical values are the same, and you can essentially equate the two. In a load with inductance (e.g., a motor) or capacitance, the two will have different values, with VA always being a larger number than watts.
 
charlie b said:
Watts and VA can be broken down into the same fundamental units of measure, kilogram-meter squared per second cubed, but they are not the same thing. [/quote]
Oh - I see what you mean.

I had translated that rc was saying that 120V VA was the same as 240V VA and 120V Watts was the same as 240V Watts.

cf
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barbeer said:
IMHO this statement is flawed.
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But for the sake of the issue at hand, it works. The only difference is power factor but when making a comparison regarding supply voltage, one can assume the power factor will be the same, so in effect, W = VA in this relationship.

J Rae (interesting handle by the way)
Power is measured in watts. Watts are watts are watts. If you raise the volts, you lower the amps, but the watts stay the same. We are billed in kWh, not kAh or kVh.
 
j rae said:
would a220v A.C. unit use the same amount of wattage as a 120v unit since
P=IE and wouldn't the 220v unit use 1/2 the amps????
Click to expand...


Not to be picky but if your current comparison is based on a factor of 1/2 then your voltage comparison should also be based on 1/2. Your question would be more accurate if you used 240 volts instead of 220 volts. Since there is no 220/120 volt system the use of 220 volts for this comparison is incorrect.
 
Oh, good grief, Charlie Brown. Is this the start of another 50-page thread?

If BTU per watt is the same for both, the cost of running will be the same.

However, the 240v unit has the potential to be more economical to wire.
 
weressl said:
This thread could have ended with a simple one-post-answer: Yup!
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But that would have been the wrong answer. Let?s take another look at the original question.
j rae said:
would a220v A.C. unit use the same amount of wattage as a 120v unit . . . ?
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Let me put two AC units on a table. One is rated for 220 volts, includes a 3 hp motor, is about 3 feet wide, weighs about 150 pounds, and would take about 2 hours to cool my master bedroom. The other is rated for 120 volts, includes a 1/2 hp motor, is about 18 inches wide, weighs about 40 pounds, and would take about 8 hours to cool my master bedroom. Back to the original question: Do they use the same amount of wattage? I think not.

My point is that the fact that the voltage is different does not tell us that that is the only thing that is different. We have been assuming too much about the intent of the question. This is not a simple matter of, ?if all else were equal,? because there are too many aspects of an air conditioner that could be different from unit to unit. There is no basis for making a simple comparison.

With apologies to the OP, this was not a question that is likely to get you to where you are trying to go. Can you try again to tell us what you want to know?
 
charlie b said:
But that would have been the wrong answer. Let?s take another look at the original question.

Let me put two AC units on a table. One is rated for 220 volts, includes a 3 hp motor, is about 3 feet wide, weighs about 150 pounds, and would take about 2 hours to cool my master bedroom. The other is rated for 120 volts, includes a 1/2 hp motor, is about 18 inches wide, weighs about 40 pounds, and would take about 8 hours to cool my master bedroom. Back to the original question: Do they use the same amount of wattage? I think not.

My point is that the fact that the voltage is different does not tell us that that is the only thing that is different. We have been assuming too much about the intent of the question. This is not a simple matter of, ?if all else were equal,? because there are too many aspects of an air conditioner that could be different from unit to unit. There is no basis for making a simple comparison.

With apologies to the OP, this was not a question that is likely to get you to where you are trying to go. Can you try again to tell us what you want to know?
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Well, I dunno.

Maybe I am just too stopeed to 'assume' that his question was concenring an application and he is just trying to decide what voltage to use, if there is any advantage of using different voltages for the same A-P-P-L-I-C-A-T-I-O-N:-?

The greatest folly of engineers to wait for all the data to come in. That's why they never get anything done......and I can say dat because I is one.......:D
 
weressl said:
The greatest folly of engineers to wait for all the data to come in. That's why they never get anything done......and I can say dat because I is one.......:D
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I disagree with that statment. I get a lot of stuff done because when I don't have all of the necessary information, I A-S-S-U-M-E. :grin:

Of course, I would never actually use that word. It would be an 'educated approximation' or something like that. :)
 
j rae said:
would a220v A.C. unit use the same amount of wattage as a 120v unit since
P=IE and wouldn't the 220v unit use 1/2 the amps????
Click to expand...

I can go along with this in theory but only if you are referring to both units having the same power rating. Just because you buy a 240v instead of a 120v doesn't mean the power will remain the same or change. Now, rewiring the same dual voltage unit then I can see where the answer would be closer to what you suspect.

I wonder. How does wiring a dual voltage unit to 240v vs 120v effect efficiency of the unit? My thinking is that the 240v may exibity better efficiency and possibly use less energy overall but I may be wrong.

Bob
 
I think Larry hit it. Pehaps this is an opportunity for the PE's to argue the finer points of AC theory, but the important thing is what is easier and cheaper to wire.:smile:
 
P=ie

P=ie

Another aspect is to consider the possible overall unbalanced load created at the meter. The energy bill at the end of the month will be higher using 120 Vac loads due to inefficiency of the equipment. (I.e. Line loss compensation) rbj
 
drbond24 said:
I disagree with that statment. I get a lot of stuff done because when I don't have all of the necessary information, I A-S-S-U-M-E. :grin:

Of course, I would never actually use that word. It would be an 'educated approximation' or something like that. :)
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OK, now you are with us.

It was safe to assume that the OP was talking about the same application.:roll: Nu?
 
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