window AC electric usage increasing a days wears on...

I plugged my window AC into a "killawatt". It was running 900 watts, then the past few days it's been climbing to 1000, then 1100, even 1200 as the day wears on -- and the sun beats down on the unit to the west side.
Suppose shading this could make a big (300 w) difference?
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Somewhat, but don't forget even if shaded, the air temperature around the unit is rising even if the unit is not in direct sunlight.
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It's been suggested and disproved that shading the outside half of ac has any notoicable effect. What you are seeing is the reduced transfer rate of heat to the atmosphere because of the increased outside air temp. This raises the high side pressure and makes the compressor work harder.
Bottom line it's not the sun beating down on it. It's the higher air temp.
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Got it -- just went outside -- unit is running at higher watts now, but it's not in the direct sunlight yet. I'm surprised it swings from 900 to 1200. 33% increase with higher temp deltas. We are around 97F outside now -- cooling to 78F inside. At 900 it was <90F.
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IAnd you expect it to run more often as well. Double whammy. Cool air ain't cheap when it's 100deg ouside :-)
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haha.. yeah.. had my hopes up when it was 90F -- running about 30% at 900W vs 60 @ 1150.. ah well...
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kansascats wrote:

Sounds like your A/C unit is too small for the area you are trying to cool. It shouldn't have to run constantly in order to keep the cooled area at 72.
Jon
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On Jul 13, 8:16am, "Jon Danniken"

A properly sized ac will run pretty much continuously when the temp is in the high 90s. A larger unit would not run enough during more moderate outdoor temps resulting in high indoor humidity making it feel clammy. You want a unit that is just big enough to hande the area but not bigger. It's perfectly normal to size one such that it can't keep up when the outdoor temp is unusually high. And the wear on them is actually less if they run for longer periods rather than startng and stopping a lot. Startup is hard on the compressors because they start in a loaded condition, the refrigerant is already near or above 100 psi when not running.
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Insightful reply - thank you. I never thought much about that. Many talk about being able to cool-down a room quickly, but the logic you supplied makes sense. Our house central AC does nearly run all the time when it's in the upper 90s. In fact on some days when the wife is cooking the temp is a few degrees about the desired temp -- it just cannot keep up. I replaced the fillter just to be sure, but I think it's just at it's max for the above average outdoor temp.
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On 7/28/2011 1:45 PM, kansascats wrote:

that's what nice about the new 2 stage AC units. I have a 2 stage central unit and as the temperature doesn't usually get real high at 2500' up in the mountains, it usually only runs on stage 1. So it runs longer and takes out more humidity. I also have a Honeywell thermostat that will over run the AC in order to reach a settable humidity level. It works extremely well. The only time I have seen it go into stage 2 is when you manually set the thermostat to a lower value or the thermostat changes the temperature due to the program.
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You might think shading the unit has no effect, but it does. The biggest thing is the whole wall in the sun. The brick or siding really heats up the whole intake area.
You need to shade the whole wall.
Greg
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I suggest you do some more research. Shading the unit makes no difference. The factor is the ambient air temp around the unit. Shading the entire area might lower that temp a degree or two from the nearby air temp in the sun but short of planting trees and waiting 10 years there's no way to do that. And 1 or 2 degrees is not going to make much difference.
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Do you have research that shows direct sun on a window unit has no effect? If direct sun on a window can add heat to a room, one would think that same heat applied to both the window and a window unit AC would have an effect.
I've seen some studies done with CENTRAL AC, where shading the CONDENSER made no material difference because as you say, it's the air temp that counts. But I have not seen the same for window units and for obvious reasons I don't believe the results for split systems can be applied to self-contained window units.
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Why would it not apply? A window unit is sort of a mini-mini split. Everything is in one big box instead of split apart by a piece of copper tubing. The condenser coil is covered with sheet metal and has a fan blowing on I it, just like a big unit. The fan sucks in air from the side vent, blows it across the coil.
What may be different is the slinger ring on the fan. That can affect the operating temperature. If the air is very dry, there will be little condensate for the fan to sling onto the coil. Does that make a difference in the readings the OP is getting? I don't really know. Easy enough to test though, by spraying some water into the vents while it is operating. It may reduce the pressures in the system and lessen the motor load of the compressor.
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Some other info...
The outdoor air is very humid here.. 20% min to 80s in the AM/PM
The indoor air is quite comfortable to me at 80F -- I'm assuming because it's pulling so much moisture out of the air. It can keep up just fine for the 12x24x8H space it's intended to cool. Every once in awhile I open the door to another 24x24 area and it even does a decent job of lowering the humidity such that I can do my woodworking over there. (I really need to poke another one of these in the wall on that side, but for now it does the job).
When the compressor runs it draws 950 to 1250 watts. Right now it's about 88F outside and drawing 1017 watts, and climbs up a bit as it runs during that cycle. When it was close to 100F, the draw was around 1250
The unit is probably 6 years old.
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On 7/12/2011 1:09 PM, kansascats wrote:

There are a lot of factors that can contribute to increased power consumption with a dirty coil being one of them but what first came to me as I read your post was the fact that the voltage in the grid may be dropping as more and more people run their AC units. When the voltage drops, the current goes up and the wattage your AC uses may also go up. Look at the voltage readings when the watts are low and compare it to the voltage when when the wattage use is higher. One thing you can do the help your AC unit is the (gently) use your water hose on a spray setting to wash the outside coil. A power stream will bend the fins on the condenser so be careful. You can do it while it's running without a problem as long as you don't direct a direct stream at the electrical covers through the side vents where you can rinse out the inside of your window unit.
TDD
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I would think voltagw is dropping or the compressor is failing, how old is it
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Clearly all of you know nothing about air conditioning. Go ask any hvac tech about the refrigerant pressures and compressor current draw as the outside air temp goes from 70 to 100.
Shading the house to reduce the heating effect on the house can make a difference. Shading the unit will make no appreciable difference. If you don't believe me go get one of those killawatt meters and try it yourself.
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