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Capacity and Direct Sunlight

Hi Brad,

Is it correct that most residential condensors are rated by ARI assuming a 95 degree ambient temp?

If this is the case, could you clarify what I dont understand? The temperature of ambient air and direct sunlight are quite different, agree? Ambient air (as per the ARI rating) has an effect on the unit, direct sunlight (surface temp) does not?


  • Mark_46
    Mark_46 Member Posts: 312

    As we know, function of a condensor is largely dependant on proper airflow through the coil.

    However, is there any studies/info available showing the effects of direct sunlight on a condensor? Surely the direct sunlight is raising the temperature of the coils and subsequently must have an effect on the refrigerant.

    Bottom line question - is it worth shielding a condensor from direct sunlight?
  • don_185
    don_185 Member Posts: 312
    other then

    Other then making the paint peel on a cheap builder grade unit the sun, has no effect on the capacity of the unit.

    Back in the old days all the old timer even myself assume that setting the equipment on the northside of the home would make it work better.We were wrong.

    I've tested them at the oceanfront on the east side and west side and there is no change what so ever when it comes to heat transfer.

  • Brad White
    Brad White Member Posts: 2,393

    A condensing unit on an open sunlit roof, especially a black one, will effectively be in a higher ambient than the intended and proverbial ARI 95 degrees. Selecting such units for 105 F. or more may be a wise move.

    My $0.02 anyway.
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"

    -Ernie White, my Dad
  • Wayco Wayne_2
    Wayco Wayne_2 Member Posts: 2,479
    I agree

    Shielding it will help. I used to take care of a chain of restaurants that had all of their condensors for refrigeration on the roof on a rack covered by a box. The box had a fan at the end pulling air through the box. The air on the entry had to go through a pad that had water from a sump below circulating through it, thus cooling the air. The high humidity didnt seem to bother the units. I've always thought that was clever. WW

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  • don_185
    don_185 Member Posts: 312
    pick your

    Pick your poison when it comes to condensing medium.As for location it does matter but, not so much if its in direct contact with the sun or under a building.

    Example..I service a system down at the ocean front years ago that was under the building alittle cooler maybe one or two degree being it was away from the direct sun light.
    However, it was a top discharge and their was only 3 feet from the top of the condenser to the bottom of building.

    I have recirculation of discharge air raising my drybulb temps causing me to send vapor up to the metering device.
    Sure spray it with a mist of water and I have a good colum of liquid now going to the metering device.

    I had to relocate the condenser out in the yard about three feet away from the building in the direct sun light and never had any further issue of the system not cooling.
  • Brad White
    Brad White Member Posts: 2,393

    ARI standard ratings for condensers vary but the "home-base rating standard" is at 95 degree ambient with the evaporator seeing an (IMHO inhabitable) 80 F dry bulb and 67 F. wet-bulb temperatures.

    Cooling towers are ARI base-lined at a 78F wet-bulb with 95 F. entering water and 85 F. leaving water, to illustrate another standard.

    Point being- you can select equipment to suit your actual needs, but for comparison they had to set a standard.

    Now, ambient air and sunlight: The additive effect of sunlight that I noted is that of air being heated on a solar-heated roof, which could be 140 degrees surface temperature with air something less above that, replaced by the real ambient which may well be 95 F. Simple as that. All effects on inlet air temperature are from secondary conduction and convection to air, not the solar radiation acting directly.

    I imagine if you had a black condensing unit you might lose a smidgen of capacity but that is not a lot of mass and a 1200 cfm fan would knock that down in a minute. But in a black field of sunlit roof? That is a lot of hot air to be drawn against. That is your new ambient!
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"

    -Ernie White, my Dad
  • Mark_46
    Mark_46 Member Posts: 312


This discussion has been closed.