Why black AC shrouds?

[DWK]

My thought is that black plastic holds up better to UV light and keeps the cover from deteriorating as quickly as white.

[JohnD10]

I have three MaxxAir vent covers on my 5'ver...two black and one is white!

The two black ones are definately much hotter than the white ones and the black ones don't seem to cool the air as much as the white one does.

I can tell this by putting my hand up against the screens inside the RV.

That is about as scientific as I need to know.

[SCClockDr]

Originally Posted by 10Ranger

Thank you all for your replies. It looks like it's unanimous that color really doesn't make much of a difference. It makes sense that once the fun starts the flow of air would be sufficient to offset whatever the temperature difference is.

I haven't really lost any sleep over the issue, just was curious. One thing I think is more disturbing to me is black covers over the propane tanks.

I suspect black is more UV resistant & will take longer to brittleize.

[JohnD10]

Originally Posted by SCClockDr

I suspect black is more UV resistant & will take longer to brittleize.

Plastic is plastic...black or white...probably both last about as long as the other!

I'll let you know as I have both.

[John s.]

I live in Las Vegas and have black covers on my unit and it doesn't matter on covers now on the color of the roof now it matters, I'm also an A/C tech. good luck and don't worry about the covers.

[Jim Stevenson]

everyone seems to be answering the issue between black and white. however, not looking at the whole note of the one that was in the shade working better that the one in direct sunlight. then when the sun went down the other one worked much better. this will happen no matter what color the shroud is black or white. you will find that if you had both the color white you would get the same results.

[bclemens]

Here is the true scoop.

-Used to be everything had white shrouds. Most everything was white sidewalls.

-As full body paint became more common, customers wanted the shrouds painted...not white. They paid for paint. The paint rarely held on to these very flexible plastic shrouds especially when they are baked in the sun.

-Around this time, black trim also became more common as it went better with painted units than white trim did. And it was tough to paint 100%...as some hinges did not like paint.

-Black shrouds started getting offered to put on painted units since this seems to be an acceptable compromise. As an OEM...we ended up stocking twice as many AC's...(as they come with the shroud on them). 13.5 White, 13,5 black. 15 white, 15 black. This became a logistical nightmare.

-with all the black trim, black tinted windows and all body paint units...it made sense that you could cut the stocking in half and reduce sku's if you just went black shrouds across the board.

So in a nutshell, it was driven by customers desire for aesthetics and an OEM's desire for logistics.

[ForestWalker]

In other words, it’s a fashion statement.

[JohnD10]

Originally Posted by Jim Stevenson

everyone seems to be answering the issue between black and white. however, not looking at the whole note of the one that was in the shade working better that the one in direct sunlight. then when the sun went down the other one worked much better. this will happen no matter what color the shroud is black or white. you will find that if you had both the color white you would get the same results.

That's all fine and dandy when you have trees around your campsite.

Very rare (but not impossible) out here in the western US of A.

By the by...I was born and raised in mid-Michigan...

A good place to be from!

This is where we were at last week in Sedona, Arizona:

[John s.]

The reason the one in the shade works better is because the ambient temperature change with the sun beating down and the shade protecting the unit. Just like a unit will work less when the temperature is in the mid 70's as compared to the mid to high 80's also the humidity has alot to do with it.

[Paulie1138]

JohnD10 yes, great to be FROM there.....LOL!

[dj-Harry]

I believe the RV air conditioners have a maximum differential temperature that they can cool down to. I think I read somewhere that it’s in the 20 degree range. Not sure if it applies to home central air units, but probably window units. So, if the outside temperature is 80 degrees, the AC can theoretically cool down to 60 degrees. If it’s over 90 degrees outside, you won’t be able to cool your RV below 70 degrees. I’m sure higher humidity and heat index (feels like temperature) also affects the ACs performance. If the outside temperature around the unit in the shade is lower than the outside temperature of the one in the sun, that could explain the difference in cooling between the two. How the black vs. white cover affects the outside temperature around the AC unit, I,’m not sure. If you’re at a permanent site, maybe try to shade the unit in the sun and see if it makes a difference.

[bclemens]

Originally Posted by dj-Harry

I believe the RV air conditioners have a maximum differential temperature that they can cool down to. I think I read somewhere that it’s in the 20 degree range. Not sure if it applies to home central air units, but probably window units. So, if the outside temperature is 80 degrees, the AC can theoretically cool down to 60 degrees. If it’s over 90 degrees outside, you won’t be able to cool your RV below 70 degrees. I’m sure higher humidity and heat index (feels like temperature) also affects the ACs performance. If the outside temperature around the unit in the shade is lower than the outside temperature of the one in the sun, that could explain the difference in cooling between the two. How the black vs. white cover affects the outside temperature around the AC unit, I,’m not sure. If you’re at a permanent site, maybe try to shade the unit in the sun and see if it makes a difference.

That's not entirely accurate.

There IS a differential temp and in many cases that is 14 degrees...but that is based on the temp of the RETURN AIR, not outside air.

So, let's say it is 90 degrees and the coach has been sitting, so its 90 in and 90 out. When the air first passes through the AC unit, it can cool it from 90, to 76 degrees (in theory). So once you have cycled the air and assuming you do not open any doors in theory, the return air is now 76, then the next pass or exchange of air, it can take it from 76 to 62. Of course that is using very simple math...it will depend on the CFM's of the AC to know how long the AC can change the whole volume of air and it will depend on the heat gain from glazing, etc. So it would likely take more than 2 changes of air volume to bring the internal air temp to a reasonable temp.

I think at some point, there might be a max temp it can bring it down to, but I think that would have more to do with the heat gain of the coach and not the ability of the AC.

As a last note, when measuring the temps of the cover, there is an air gap behind the cover. So while the black for sure will get hotter in the sun, that does not tell the whole story of the temp of the coils, etc. No doubt, the black shroud (at least we would assume) has "some" level of impact on the cooling. But I don't think you can just measure the surface temp and assume thats a direct correlation.

[dj-Harry]

Thank you, but this is from an AC Company:

How Much Can Your Air Conditioner Cool: Realistic Temperature Differences Between Inside and Outside Air

We tend to think that we can set our air conditioning thermostats to whatever temperature we desire and have the air conditioner do its job no matter what. However, this is not the case: there is a limit to how much an air conditioner can realistically cool when comparing temperature differences between inside and outside air. Wm. Henderson is an air conditioning company that understands the various limits of AC systems and can prevent you from needlessly running your air conditioner too much on the hottest days.

Temperature Differences between Inside and Outside Air

Generally speaking an air conditioning system is designed to accommodate up to a 20 degree difference between the outside air and inside air while still keeping around a 55% humidity level which is comfortable. This means that it is 80 outside your AC can easily reach 70 degrees, since that is only a 10 degree temperature difference. So even if it is 90 degrees out your air conditioner should still easily reach the 70 degree mark. However, if it is 100 degrees outside, it will be nearly impossible to reach 70 degrees inside without the air conditioner working completely overtime and causing problems such as excess humidity.

If you have your air conditioner set to a temperature that makes that differential more than twenty degrees you will likely run your AC all day long and still not quite reach those desired temperatures. This becomes a waste of money on your end by overusing a system that was not designed to accommodate what you are trying to do.

A good rule of thumb is during the hottest days when the dial reaches 100 degrees it is best to set your AC to somewhere between 75 and 80 degrees. You can also supplement that slight temperature difference with closed curtains on sunny side of the building, running ceiling fans and portable fans in rooms which people are present, and keeping a tall glass of ice water on-hand. Additionally, make certain that your AC is properly maintained in order to eliminate the possibility of losing efficiency and money through items which could have been easily fixed like replacing dirty filters and cleaning coils.

[bclemens]

That's probably a better description...but I didn't say it was wrong, just not entirely accurate, nor is my description entirely accurate. There are so many variables at play. I have seen AC's overcome a greater than 20 degree difference. Likely the humidity inside was higher...but with ALL the window shades drawn, cab reflectors up we've had it down to 72 when it was around 96-98 with a black AC shroud. 2" thick laminated walls with higher density block foam. I am also pretty sure a stick and tin travel trailer would not get the same results, even with a white AC shroud, unless the walls were 4" thick.

The 14 degree drop, was given to me by our AC supplier.

[SeaDog]

I think you guy are mixing apples and oranges. the temp maintained inside an RV is not an indication of how well the indoor coil (AC) is working regardless of the temp outside, all that temp is an indicator of how well the RV is insulated and if the AC is sized correctly.

Temp difference across an indoor coil is measured at the return air and the closest cold air outlet. the best A good working AC can make is a 20* drop with clean filters and proper air flow.

Rule of thumb in the HVAC industry is a properly sized AC unit on a house on a 100* day will be able to maintain temp if the unit is started prior to the interior reaching 80* If you let the interior get hotter then that prior to starting the unit may not be able to remove the heat the house is generating. Remember you cannot add cool you must remove heat.

[Paulie1138]

dj-harry, that guy is a bit wrong. He does not take into account the fact that yes, a temp differential between outside and inside air will be 20 degrees. He does not account for the fact he is no longer trying to drop the OUTSIDE air another 20 degrees. The A/C is now using that 20 degree cooled air fed back into the INDOOR portion of the unit, thereby lowering that already cooled air, even lower.

Otherwise, we would fry here in the deserts on a 120+ degree day. Everyone I know here expects it to be at or below 80, a temp difference of over 40 degrees.

I get the same results inside my camper. You have to be able to cool the inside enough to overcome whatever heat gain of the space you are cooling. Otherwise, you will reach that point where your A/C can no longer cool that space below that point.

[rockfordroo]

I think your AC company guy is trying to sell bigger AC units.

Bottom line on cooling is that the AC will remove a certain number of BTUs/hr. So long as the heat flow (BTUs/hr) INTO the house/building/RV through the walls/windows/doors, etc. is less than the heat being removed by the AC (BTUs/hr), the temperature in the house/building/RV will drop (once the humidity is removed).

BUT REMEMBER: As the temperature inside drops (i.e., the temperature difference between the inside and the outside increases), the heat flow into the house/building/RV will INCREASE, because the heat flow is proportional the temperature difference. So as the AC is cooling the building, the heat flow into the building is increasing. So long as the AC can remove more heat than what is coming in, the inside temperature will continue to drop until either a) the thermostats setpoint is reached or b) the AC can't keep up with the incoming heat load anymore.

Note also, however, that as the outside air temperature goes up, the efficiency of the AC goes down. That 13.5K or 15K BTU/hr they quote you for your unit is at a specific set of conditions. We almost never operate them at those conditions, so the heat removal capacity of our AC units is almost never what they claim. So as the outside temperature goes up, the actual BTU/hr it can remove goes down.

Again, your AC will drop temperature until a) the thermostat is satisfied or b) the incoming heat load becomes greater than whatever your AC can do.

[Paulie1138]

Nice explanation rockfordroo

[formerFR]

I just like the black better...


oh well.