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Does an AC compressor located in full sun work harder than one located in the shade?

Our AC compressor is located on the south side of our Florida home and it seems to me that if it were shielded in some way it would not have to work as hard - is this correct?

Asked by Chuck Mucciolo
Posted Sat, 02/22/2014 - 08:40
Edited Sat, 02/22/2014 - 15:47

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1.
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Chuck,
Q. "Does an AC compressor located in full sun work harder than one located in the shade?"

A. No. One of the best articles on this topic, "The Nonbenefit of Shading Air Conditioners," was published in the July 1995 issue of Energy Design Update. While it is not available on the web, you may be able to find it in a good academic library.

You might also look at "Air Conditioner Shading Shows Minimal Savings," in the Sept/Oct 1995 issue of Home Energy.

The temperature of the metal box housing the condenser is irrelevant. The relevant material (fluid) for heat transfer is outdoor air. Outdoor air is at the same temperature on the sunny side of your house as it is on the shady side of your house.

Once the outside fan comes on, a tremendous volume of outdoor air flows across the outdoor heat exchange coils.

While it's true that a thin film of air near siding that has been warmed by the sun, or a thin film of air near a metal box that has been warmed by the sun, is at a somewhat higher temperature than the outdoor air, the volume of air in that film is insignificant compared to the large volumes of air pulled through the condenser.

I'll quote from the July 1995 article from Energy Design Update, "The Nonbenefit of Shading Air Conditioners":

"The results of two-year field study by the Florida Solar Energy Center (FSEC) show that energy savings [resulting from shading air conditioners] are minuscule at best. ... The problem is that a typical 3-ton unit moves about 2,800 cubic feet of air per minute or 170,000 cubic feet per hour. In order for a shading device to be effective, it would have to shade the entire area in which that air is contained. ... Shading just the air conditioner does almost nothing, says [researcher Danny] Parker. Even at peak sunlight (1,000 watts per square meter), shading two-thirds of the sunlight form a 3-ton air conditioner would theoretically reduce the cooling air temperature by only 0.3 degrees F and thereby increase the air conditioner efficiency by less than half a percent. ...

"The results [of the study] show that the house with a trellis saved only 3% in energy and the house with plantings actually showed an increase of 18% in energy use after the shading was installed. Parker hypothesizes that the reason for the increased energy consumption was that the plantings caused some of the exhaust air to recirculate back into the air conditioner."

Answered by Martin Holladay, GBA Advisor
Posted Sat, 02/22/2014 - 15:45

2.
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Seems that the conclusions you drew from that study might be a stretch (possibly contradictory). The study implies that shading the box doesn't help much - but to say north vs south side of house would have the same results is not true. Although OP didn't mention sunny vs shade side of house - just shading his southern facing unit (in which case he's mostly out of luck)

The study concluded with stating a trellis (shading a good chunk of area surrounding the AC) saved 3%. I would presume that north side would even have a higher result (~4-6%) of saving due to the effective shading 24/7 (vs a trellis which likely wouldn't be effective all day due to sun angles). If possible i would take those savings if the cost wasn't impacted (original install) or if the aesthetics of landscaping/trellis were of benefit to the house/value.

Everywhere it discusses the shading of just the unit. No where does it talk about location of it...just retrofit install plantings/blocking (hard to block the entire side of a house...~500-1000sqft)

Now of course entire study has a section that mentioned location testing...

Answered by Nick T - 6A (MN)
Posted Sun, 02/23/2014 - 11:14

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