10K BTU Window Unit

acehJune 13, 2011

I noticed that the default temperature setting when you first plug in this unit is 72 degrees. My curiosity got the best of me so I went out to the meter and counted the revolutions per minute it would make at this setting. To my surprise it makes fewer revolutions per minuite at 72 degree setting than it does a 75, 76 or 78 degrees settings.

How can it use less electricity when it's using more cooling power?

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dadoes

I don't think you're understanding how the machine uses power.

It pulls the same amount of power at all times when the compressor is running, regardless of what is the temperature setpoint. The compressor (cooling pump) is either on or off. As an example, say it uses 850 watts of power when running. It (the compressor) is either running and pulling 850 watts, or it's off and pulling zero watts. This actual wattage draw of the unit as a whole will vary a little depending on the circulation fan speed, but the comparable difference brought into play by varying fan speeds is largely insignificant as the fan itself uses much less power than the compressor. Assuming electronic controls, the unit as a whole won't ever really drop to zero watts, as the control board pulls a few watts, and the fan may continue to run when the compressor cycles off.

Setting the unit to a colder (or warmer) temperature simply causes it (the compressor) to run for a longer (or shorter) period of time to attain a colder (or not as cold) indoor temperature. Setting a colder temperature does not make it instantaneously run harder/faster and pull more power (other than if the circulation fan is running at a higher speed, but again, that's insignificant compared to the compressor).

The difference you observed on electric meter rotation is probably because some other device (refrigerator, water heater, clothes dryer, microwave oven, pool pump, garage door opener, or whatever) had coincidentally turned on (or off) at the higher temp (or lower) temp settings.

Some air conditioning systems have a true variable-speed compressor that runs faster or slower in response to the cooling load ... but that is not common on window units.

    Bookmark   June 13, 2011 at 7:31PM
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aceh

dadoes,

Thanks for clearing that up. Hope you don't mind another question. The window unit has digital temperature setting. I normally run it in Econ mode with Auto Fan (which adjusts the fan speed according to the needs of the room). In Econ mode the unit will shut OFF and the fan will STOP when the set temperature is reached. During the hottest part of the day, the unit will have long runtimes before shutting off. During one of these long runs, is the compressor running all that time or does it cycle on and off even though the unit has not reached the set temperature to shut off completely?

    Bookmark   June 13, 2011 at 8:29PM
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dadoes

The compressor should be running the entire time until the setpoint is reached, and the fan should *never* turn off while the compressor is on. The fan may (or may not) run for a minute or so after the compressor stops to dissipate residual coolness off the evaporator coil. Some (more deluxe) units with electronic controls may run the fan occasionally/briefly during the "off" period to refresh the thermostat reading due to airflow across the sensor otherwise being stagnant while the fan is off.

    Bookmark   June 13, 2011 at 10:04PM
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aceh

Thanks again dadoes.

    Bookmark   June 13, 2011 at 10:33PM
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