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Trombe Wall Variation - Page 2

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Posted by Eeyore on April 21, 2009, 3:28 pm

Tim Jackson wrote:

Sorry, I don't quite get it. Low-E glass AIUI can do nothing but improve the
performance of a Trombe Wall by maximising solar gain.

Maybe you could simplify it for me ?


Posted by Tim Jackson on April 21, 2009, 7:59 pm
Eeyore wrote:

I don't disagree with you.  I was concerned that the Wiki you referred
to looked a bit flakey, and was newly edited.  However as I mentioned
elsewhere, I have since looked into it in more detail and now understand
where it is coming from.

It's just that there is so much hype around glazing, marketing people
seem to go to some lengths to conceal the facts in case anyone realises
that it is not actually a very good investment.


Posted by Eeyore on April 21, 2009, 8:48 pm

Tim Jackson wrote:

I understand you scepticism but low-E glass has been around a long time now.


Posted by daestrom on April 20, 2009, 9:34 pm

Actually the statement is correct with regard to window glazing.  The glass
itself conducts heat, but the most any gas between the panes is an excellent
insulator.  The only 'trick' is having the spacing just right.  To much
distance between the panes and the gas inside will start to convect between
the cold pane, down and up the warm pane.  With a small enough gap this
convection is greatly reduced because the downward motion along the cold
pane interferes with the upward motion along the warm pane and the
convection currents never really develop.

Well designed windows you have convection from the room warming the inner
pane, radiant transfer from the inner to the outer pane and convection
currents on the outside cooling the outer pane.  Low-E coatings minimize the
middle step.


Posted by Jim Wilkins on April 20, 2009, 10:14 pm
When I built my multilayer window inserts in ~1981 the suggested
spacing was 20mm or 3/4". The two added layers of polyester film add
enough insulation to the original 1970 windows that the IR temperature
of black tape on the film is only 2 - 3F lower than the same tape on
the wall nearby, when outdoor temp is well below freezing. There's
some variation across the walls and on upwind and downwind sides of
the house so I don't have more precise measurements.

Pyrex is naturally low-E and takes forever to cool after blowing
labware out of it. It's dangerous because it doesn't radiate enough
heat to warn the hand even when it's nearly red hot.

Jim Wilkins

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