On Thu, 15 Jul 2004 19:47:56 +0000 (UTC), "Franz Heymann"
wrote:


wrote in message
.. .
On Thu, 15 Jul 2004 05:52:23 +0000 (UTC), "Franz Heymann"
wrote:

That is not true. It absorbs infrared radiation.

I thought you might says that :-)

and you didn't mention black body radiation.

Firstly, the glass is not a black body. {:-))

{:-)) ---------the trademark of the real Franz.

Yes. In addition I also don't talk as much rubbish as the impostor
using my name. {:-))
The "{" is a matter of wishful thinking, since I have practically no
hair left.

hair? I thought you had bumped your head on the greenhouse door frame
:-)

Incidentally one winter I measured the temperature at floor level and
ceiling level in the living room.
Ceiling 30DegC
Floor 14DegC

You have a point. The major reason why a greenhouse retains heat is
actually that it prevents the hotter interior from cooling by large
scale convection. All this stuff about the glass absorbing the
infrared radiation emitted by the contents of the greenhouse is small
beer compared with the simple mechanical shielding offered by the
structure. This is illustrated nicely by the fact that a greenhouse
cools off when all the ventilators are opened wide.

[snip]

To really appreciate this you have to see the Mickey mouse automated
heating control systems in the local green houses, where they grow
orchids 25,000 at a time.
Gas heated hot air blowers heat the green houses, at max temp all the
windows open automatically, hot air rushes out, temperature plummets,
all windows shut and gas comes back on again. Goodness knows how much
gas they are wasting, but I am not surprised that North Sea gas is
running out.
--
Martin