Re: [VACList] White Roof

[John Sellers <sellersj@xxxxxxxxxx>]

Toby,

I don't agree with this conclusion.  (BTW, I'm also an engineer.) 
Here's why:  An object sitting out in the sun, like the roof of an
Airstream, is subject to two radiation processes.  It is absorbing heat
from the sun, proportional to its absorptivity over the solar spectrum. 
At the same time it is radiating heat to the sky, proportional to its
emissivity over its own radiant spectrum (at much longer wavelengths
than most of the solar energy).

Polished metal surfaces have low absorptivity at solar wavelengths but
also low emissivity at thermal wavelengths.  What you want is something
with low absorptivity over the solar spectrum but high emissivity at
thermal wavelengths--i. e. white paint.  I understand Airstream painted
the roofs of some of their early trailers white for that reason.

However, I wouldn't expect the difference to be very
significant--especially if there's any breeze blowing--because radiation
is a relatively minor part of the total heat transfer from an object at
near-room temperatures.

Best bet is find a nice shady spot!  Lacking that, I wonder if anybody
with a smaller trailer has tried to rig a whole-trailer awning--like a
tent fly.  If I were planning to camp out in the sun very much I would
sure think about it.

Best regards,
John Sellers
WBCCI/VAC #1587
1960 Pacer
(Dayton, Ohio)