# Which AC Unit Uses Less Power?

I have 2 window units:
1. an 18,000btu 220V 2. a 10,000btu 110V
I remember reading somewhere that, while obviously bigger & more powerful, the 18K unit is cheaper to run because it's 220V. This is counter-intuitive but does anyone know?
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Look at the amp rating. That will tell you the total amps used.

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New units are much more efficient than old. and no two different brands are the same, for new units go by the printed rating on eficiency.
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Most likely the bigger unit will be cheaper to run. Even if it uses less amps, the power consumption will be higher because the voltage is higher. Power is volts times amps times power factor. The power factor applies to loads with motors, like the compressor and fan motors. The power factor should be between 0.9 and 0.95 for both units. so all you need for comparison is the volts times amps for both units. Ideally, you should measure that whle the units are running, not go to the nameplate. The amp rating is the maxmum amps, not the normal running amps. My heat pump is rated 12.0 amps, but normally draws about 6 to 8 amps when running.
That said, if your load is 1-1/2 tons, you will need the bigger unit to cool the space. If the bigger unit is more efficient (Hgher EER) it could be cheaper to operate than two smaller units.
Stretch
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Dick wrote:

A question that sounds easy, but is complex.
Let's start with your question about using less power. If you mean how much total electrical power (and cost) it uses per minute while it is in cooling mode, you will need to check the number of amps and multiply the 220V (likely 240V) times to and then compare them.
Of course this does not really help since one will be producing more cooling than the other. Generally the larger units are more efficient using less total electricity to produce the same amount of benefit and thereby often run less long so over a 24 hour period they may use less total electricity.
While it is often true that a 240V unit will be more efficient than a 120V unit it is not always the case. New units should carry a SER number, higher is better. The SER number tells you how efficient a unit is at in test situations and fairly compares units using different voltages.
Finally it is not all about cooling. Humidity control is also important. Have a unit that is too large can short cycle and not be able to remove enough moisture from the air to be comfortable.
--
Joseph Meehan

Dia duit
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Very simply put, a 220V unit does not use less electricity than a 110V unit. It does run more efficiently though than a 110V, which in turn saves you electricity.
When you pay your electric bill, you pay for watts. The electric company couldn't care less how much volts or amps you use. It's watts they are interested in. So now lets compare apples to apples for a second. Lets say you have 2 identical 10,000 BTU A/C's. One is 110V rated at 10 amps, while the other is 220V rated at 5 amps ( as a rule of electricity if you double the voltage , the current will decrease by half). Now as the other poster stated. Watts=V*A. So both units in theory use 1.1KW. But because the 110V unit uses 10 amps, there is more of a voltage drop across the electrical wires from the breaker panel to the A/C. Resulting in reduced voltage at the outlet, which makes the A/C run less efficient. But the 220V unit only uses half the amps, resulting in less voltage drop, less heat across wires, more efficient. So to answer your question, the 18,000 BTU in all likelyhood does use more electricity than the 10,000 BTU because it is a bigger unit, not because it is a 220V unit.
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Then you seem confused. "Power per minute" is meaningless, like "miles per hour per hour."

As in "electrical energy," ie kilowatt-hours, ie kilowatts X hours of use.

Not much, I ween.

No. That's power, the rate of energy usage. We pay for energy usage, ie power times time, like total miles traveled, vs miles per hour.

A Btu is a measure of energy. Heat power is measured in Btu per hour. Power is the rate of energy useage over time.

Times the power factor, eg 0.8 for a small motor or 0.4 for an old undercounter fluorescent light.

IME, real numbers would show a miniscule efficiency difference.
Nick
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wrote:

I vote for the lower BTU unit every time. But that is assuming that the EER is approximately the same for the two units. Always shop for and buy the highest EER you can find.
My window units are about 11.0 EER. Normally, the cheapo units are 9.5 EER.
220 units might be a couple of percent less power at the most. Not that much of a difference.
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This is Turtle.
In No way is a 16k window unit cheaper to run than a 10K window unit, Period !
If you had a 16k btu window unit and another 16K btu window unit and all were the same but one was a 110 volt unit and the other was a 220 volt unit. there will be NO cost difference between running either one. The ideal of a difference is a Myth of the electric world.
TURTLE
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