Quote:
Originally Posted by JSH
Your experiment does not support that conclusion.
Your experiment shows that chrome wrap over white paint outperforms white paint alone.
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I already mentioned that. It does however confirm the whole premise of the thread that chrome wrap will make your car cooler, even if it's already white. It also debunks the theory that 'anything chrome left in the sun will get hot', if it's getting so hot, why isn't that transferring to the sheet metal?
There's also observational data that suggests chrome is cooler than white. My chrome roof stays wet all day in the sun on a hot day. That never happened with a white van.
The maths also supports chrome being cooler than white.
Chrome: out of 100W of IR energy 3W gets through
White: out of 100W of IR energy 10W gets through
Of the 3W that gets past our chrome surface 3% gets dissipated or 0.09W
Of the 10W that gets through the white surface 10% gets dissipated or 0.1W
Leaving us with a net heat gain of 2.91W for Chrome vs 9.9W for White.
It's a bit like leaving a window open at night because the more mosquitos you let in the more will get out.
Given enough time (probably longer than a days worth of sunlight) I suppose it's possible for emmisivity to catch up and build up heat, but it's really not relevant to the discussion. I'm not chroming the underside of the roof, so the majority of the heat is reflected by the top side, but painted underside can still emit the tiny bit of heat that gets through.
There's no way heat can be trapped by emmisivity if the coating is only on the top side (again exactly like building insulation).
I've been burned by hot tools left in the sun, we all know that. But I left a nice shiney chrome wrench outside on a 100 degree day, and it never got hotter than my white painted control. It's say most of the time the offending scorching hot tool is silver rather than chrome, and might have a textured surface (like all my shifting spanners which seem to be the main culprit). There's also the fact that if you leave it on burning hot driveway, it will also be burning hot, I know my driveway can easily reach 160* plus and it's not even a dark colour.