Window Unit 10K - 338 Sq ft to cool

acehJune 18, 2011

Hot, humid South Eastern Louisiana temps high 90's with heat index of 100+.

During the hottest part of the day, is it normal for the unit to run approximately 1 hour and 20 minutes with 20 to 30 minute breaks in between?

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david_cary

Sure. In fact, that is pretty close to ideal. Ideally really is running constantly in the hottest part of the day but you are very close and that is great with a window unit.

    Bookmark   June 19, 2011 at 6:27AM
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aceh

I have a central A/C and Heating unit, but I use the window unit during the day since there are several rooms which don't need the A/C at that time.

I'm used to the central unit cycling on and off as it is better at maintaining a temperature. Therefore I couldn't help but think that the window unit might run out of freeon (lol) or the compressor may get over worked running for long periods. I didn't know that long run times were the ideal with window units.

    Bookmark   June 19, 2011 at 9:44AM
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david_cary

Long run times are ideal for all a/c units. They wear on start and stop and they also remove humidity better with long run times and they are also more efficient that way.

    Bookmark   June 19, 2011 at 6:58PM
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dadoes

aceh,

A 100% properly sized unit will run 100% of the time, using just enough energy to maintain the target temperature. Problem is that's impossible to achieve across the wide range of conditions under which a system must operate. As explained previously, the compressor is either full-on or full-off (other than dual- or two-speed or variable-speed compressor systems). So, they're sized to maintain a reasonable indoor temperature on 100% run-time at the "typical" highest outdoor temp a given area experiences.

Remember ... air conditioning doesn't make cold, it moves heat from inside to out. BTU rating is the amount of heat that can be transferred in 1 hour. The system is constantly "fighting" against heat gain (radiating through roofs and walls and windows and doors, outdoor hot air infiltration, indoor heat sources such as human bodies and cooking and lighting and use of appliances and electronic devices, etc.). If said heat gain exceeds the capacity to remove it, the indoor temp will rise even when the system is running continuously. Much less heat gain, the capacity for removal far exceeds the gain so the system quickly reaches the target indoor temperature and cycles off ... not necessarily because that's the ideal situation, but because there's no way to throttle-back the unit's capacity to match the load (fan speed can be reduced, but that's not the same thing).

Two-speed central systems address the capacity-match problem to a degree (LOL) by cutting back to low compressor speed and running for longer periods.

This reminds me of a neighbor up the street from my parents. After several people in the area got two-speed systems, said neighbor bought one also, and then got upset at discovering that it ran for hours at low speed. He insisted the contractor "fix" it to operate at only high speed so as to run hard and fast and short to reach the setpoint and shut off ... thereby totally quashing the reason for investing in a two-speed system.

    Bookmark   June 19, 2011 at 10:11PM
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aceh

I appreciate all the information on AC's. This board has been a real learning experience for me.

Question: When a person buys a properly sized Energy Efficient unit, doesn't long run times cause the bill to go way up which to me seems to defeat the purpose of "Energy Efficiency"?

    Bookmark   June 20, 2011 at 2:31PM
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ionized_gw

What is the alternative. buy an air conditioner that is too big? That would turn on and off, consumer more power than the smaller one while running and be less comfortable.

Answer: no.

It seems to me that on for 1:20 and off for :20 are long times. I would expect more frequent cycles. If you are comfortable, however, it works.

    Bookmark   June 20, 2011 at 6:50PM
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