Hot Spars

[BlueScarecrow]

The outside of my coach is painted a dark blue. The skins are a magnet for heat. Being that they are riveted to the structural spars of the coach, that same heat is being transmitted conductively to the spars. The spars, now at 150+ degrees are conducting that same heat to the aluminum ceiling panels where it is being distributed throughout the coach, bringing the inside temperature past 115 degrees.

No wonder people install 3 rooftop air conditioners.

I see some sort of thin tape that MCI applied, I guess, to help curb the process, but that tape is hard and crusty and no longer works.

If the space shuttle can travel through heat over 1000 degrees, I should be able to make my coach into a thermos bottle.

Anybody have any ideas?

I want to be cool again man! 


Thanks!

[TomC]

After stripping the interior of my bus, I screwed 1x2 fir strips horizontally to the wall uprights. Then had 2.25" of spray foam installed. But since you can't do that, repainting white will make a big difference. Good Luck, TomC

[Dave5Cs]

That separation tape is not for heat it is for dissimilar metals so they don't touch each other and cause corrosion. Like steel against aluminum etc.

[BlueScarecrow]

Never thought about the electrolysis issue. Hmmmmmm.

I guess MCI didn't give it much thought; having a 5 ton compressor in the back, pretty much took care of the heat problem here in Phoenix.

I like the wood furring strip idea... thanks!

[Iceni John]

http://www.deansteelbuildings.com/products/panels/sr-sri-by-color/
This chart should be the primary determinant of exterior color, at least if you live anywhere the sun ever shines!

I'll be painting my bus's sides Almond.   It has almost as good solar reflectivity as white, and it's a stock Rustoleum color so no worries about getting touch-up in the future.   Unfortunately the dark blues are not too good for SRI, as you've found out.   When I repainted the roof I used the ceramic insulation pixie-dust in the white paint  -  I think it made it slightly cooler / less hot, and every little bit helps.   My eight big solar panels up there do however make a BIG difference to interior temperature.

In an ideal world you'd insulate everything, but sometimes it's just not possible or feasible.

John

[DoubleEagle]

The Dean Chart is interesting in that the Almond color has a higher SRI than Polar White and Oyster White, which does not seem logical. I have to wonder if a mistake was made in compiling the chart.

[Iceni John]

A while ago I painted swatches of different colors onto a sheet of aluminum to see which would be hottest in the sun.   With a cheapo IR thermometer (not very accurate at best) and my hand, it seemed that pure gloss white and almond had the same temperature, School Bus Yellow and light grey were slightly hotter, gloss black was hotter still, and surprisingly the bare unpainted aluminum was the hottest.   Was this a scientific test  -  heck no, but it confirmed why light colors make sense in hot climates.

And that's why I'll be painting my bus Almond!   Is it the nicest color  - no, not really, but it should help keep interior temperatures reasonable.   White shows the dirt too much, otherwise I would use it for the bodysides.   The roof color is more important than the sides  -  that's where most sunlight hits, so it has to be white.

John

[Lin]

I once bought a powder made out of tiny foam beads that supposedly decreased that thermal transfer when added to paint.  I ended up adding it to the roof coating the last time I did it.  I really do not know if it made any difference.  Anyway, I believe there are thermal paints that might help.

[Dave5Cs]

Looked like silver was the best at the top. Mine is silver with white top.

[luvrbus]

Funny thing about metal and paint my bus is setting in the shade both the black and white paint are identical in temperatures the ambient temperature is 104F so is the metal     

[Ed Hackenbruch]

 I have shot temps of as high as 184 degrees on the side of my bus on a flat black panel blocking out one of my windows.....the gloss black piece right next to it was a bit cooler.

[Lin]

According to that chart, which has three different whites, snow white is the most reflective.  I am not sure I could tell the difference between snow white and polar white though unless there is a dwarf around to help.  Dark green seems to be the least, and black is not included.  I once read that dark green absorbed more heat than black but do not really know if that is true.

[sledhead]

I did mine like Tom C but used 3 @ 3/4 " strips at the top centre and 2 @ the start of the roof at the walls  of ply for both added spray foam and to stop the heat transfer   + a lighter colour would help

dave

[gg04]

Not sure where they got their chart numbers. There was a link on here at one time to the NACA study. Most reflective is a shade of blue. The almond is a pale shade, actually used by Ford as Wimbledon White..rdw

[luvrbus]

The new State trooper patrol cars in Az are now painted shades of blue and they say because of the heat here the blue is supposed to be better than the old white for heat fwiw it is a pretty shade of blue