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Would adding a shade (i.e. a piece of plastic) at the back of an A/C increase the efficiency of a window unit A/C? I'm not talking about covering the fins but rather placing a sheet of plastic above to create shade without obstructing the air flow. Or does the forced air easily suck off the heat regardless of how much the sun is shining on the unit?

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  • $\begingroup$ No but they could benefit from being wet ;) $\endgroup$ – joojaa Jun 7 '16 at 14:41
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There will obviously be some performance boost if you shade the fins/housing, but it will be negligible, since the ambient temperature around the a/c unit will not be affected by shading the unit itself. the ambient temperature on the north side of a structure can be considerably lower than the south or west side - my house has a carport on the north side of the house and I frequently see temperatures that are 10 degrees cooler than the south side of my house.

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  • $\begingroup$ Yeah, since the compressor uses pressure to expel the heat and the fan carries it off I don't see how it would have much effect. $\endgroup$ – Ruminator Jun 14 '16 at 17:38
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The case temperature has negligible effect on the operation of an air conditioner. (It's already a light color, right?) There's so much air running through the unit that the heat transferred through the case is a tiny fraction of the heat transferred directly to the air. Indeed, any heat flowing in through the case is mostly transferred directly to air flowing right back out again.

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  • $\begingroup$ I was envisioning shade over the fins at the back, not over the case. I.E. extending from the case about a foot or so to shade the fins/coils. $\endgroup$ – Ruminator Jun 7 '16 at 14:05
  • $\begingroup$ A variation on the same question would apply to central air units which are usually sitting out in the sun on a roof. Would they benefit from being under a shade? $\endgroup$ – Ruminator Jun 7 '16 at 14:07
  • $\begingroup$ The fins are heated much more by the compressed coolant flowing through them than they are by the sunlight hitting them. $\endgroup$ – Dave Tweed Jun 7 '16 at 14:10
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    $\begingroup$ This is a common misconception: just because the case appears to be off-white doesn't mean it's reflective in the infrared. It should be, but you can't guarantee it is. Further, just because the primary heat load is from the compressed coolant doesn't mean there's no advantage to blocking the sun. Think how much cooler it is in the shade compared with sitting under direct sun. Granted the overall air temperature is pretty much constant, so the local heat load from the housing is likely to have a significant effect only in the first few minutes of fan operation. $\endgroup$ – Carl Witthoft Jun 8 '16 at 12:42
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I wrote to the manufacturer of the particular unit that I recently purchased and posed the question and this was their response:

Thank you for contacting **********, ***********.

I will be happy to assist with answering your question about the efficiency of the air conditioner.

If you install the air conditioner where direct sunlight will be, it will possibly causing the appliance to run a little longer. The appliance will not be affected by performance if you decide to not install it in a shaded area.

I hope this information is helpful to you and if you need additional assistance please reply to this email. Thank you for being a valued Frigidaire customer.

Sincerely,


Correspondence Specialist

And I also received this follow-up:

Per your manual it states “Install the room air conditioner on the shady side of your home. A window that faces north is best because it is shaded most of the day.” So this will be energy efficient to store it in a shaded area. Due to the fact that air conditioners also work based on outside temperatures.

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  • $\begingroup$ I appreciate that you contacted the manufacturer, but that has to be the least helpful and vague reply from them! "it may run longer" and "it won't affect performance" do not mean the same thing. It is either one or the other. $\endgroup$ – hazzey Jun 10 '16 at 12:59
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    $\begingroup$ @hazzey What I think they are saying is that the room temp will not be affected but it will require less energy to achieve it. $\endgroup$ – Ruminator Jun 10 '16 at 13:07
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The housing under direct sun will be much warmer but its contribution is minimized by some factors.

-1 the surface area of the housong compared to densely placed fins of the radiator/condenser.
-2 the fan positioned in a way to create the greatest current of air blowing through the fins, getting chilled, while stagnating around the walls of the box.
-3 in some models the the flow of hot air near the walls of unit has been impeded by partitioning the space in a way to insulate the current of chilled air.
-4 choosing the window were the inflow of air is from a shaded area has more impact. Consider trees and their moving shadow in the hottest time of the day. In Los Angeles the difference between shade and sun radiation is 10 to 15 degrees. So if we use tributary source from a shaded area it makes a big difference.

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Yes. If we calculate by refrigerant chart, efficiency is better if temperature difference is smaller (because the vapor-liquid dome is smaller to top, comparing low pressure work with high pressure work, with the same low pressure line length, the higher high pressure the smaller high pressure line length - thus efficiency smaller). So if condenser is colder, efficiency will be better.

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  • $\begingroup$ I haven't tried it. It might be difficult to measure the difference. $\endgroup$ – Ruminator Jun 8 '16 at 10:06
  • $\begingroup$ @WoundedEgo you're right that this is a difficult thing to measure. But since the efficiency is directly dependent on the delta temperature between the air and the coils, cooler air is always better. $\endgroup$ – Carl Witthoft Jun 8 '16 at 12:45
  • $\begingroup$ @CarlWitthoft I just wrote to the manufacturer. I'll report back with what they say. $\endgroup$ – Ruminator Jun 8 '16 at 12:55

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