On 15/12/2011 11:21, RobertL wrote:
On Dec 14, 3:43 pm, Martin
wrote:

Reflecting that away from *outer* walls is worthwhile, but far better
with insulation behind so the foil is thermally isolated.

I have seen someone get caught out by an old style linear regulator PSU
they put in a basic folded shiny aluminium case and it got so hot that
it went into thermal shutdown. After painting it black it was60C.

So, in fact, the best colour to paint radiators is black, not the
conventional white.

The difference is extremely marginal.

The visible light colour bears no relation to the thermal IR properties.
Almost *any* colour of paint that is not mirror finish metallic radiates
like a black body at the sort of thermal IR wavelengths characteristic
of the Earths ambient temperature.

Tactically if you want to keep a building cool painting it brilliant
white is the optimum. This was done of observatory domes until quite
recently when modern aircon became preferred and the domes are now
painted with a very sophisticated semi metallic off white paint system
that has neutral heat loss properties under a clear night sky.

The old stuff used to radiate too well leading to cold air currents
spilling over the edge of the dome slit and turbulence.

Regards,
Martin Brown