"Andy Hall" wrote in message
...
On Tue, 12 Aug 2003 11:08:37 +0100, Tony Bryer
wrote:

In article , Andy
Hall wrote:

However this misses the context completely. Far more heat
is going to be coming into the property through the windows
and walls than the roof anyway. The same argument applies,
only even more so because the solar gain through the windows
will have to be added in for the summer case.

I'm not 100% convinced: at the weekend I pointed my laser
thermometer up into my loft and it was 52C - there's a long
south facing slope acting like a giant solar panel. But of
course at night the reverse happens and the roof acts like a
big cooling radiator.

OK.

If I use my example of the 8m x 8m house
and the current Building Regs
U value of 0.16, and let's say the room
temperature of the upstairs
rooms is 25 degrees.

Through the upstairs ceiling, the major
heat gain would be transmission through
the insulation (and I suppose bridging through
the ceiling joists if they weren't covered.

Heat gain would then be

64 x 27 x 0.16 = 276W.

Also, due to convection, that heat would
remain near the ceiling.
This doesn't suggest a major heating
effect to the rooms

Wrong!

A pool of heat (hot air) is trapped against the ceiling. This pool of heat
heats the thermal mass ceiling plaster and joists and in turn this acts as
large radiator radiating down haeting the people and room below. That is
why with windows not up to ceiling level it is best have a small ventilator
at ceiling height, or on the ceiling. The vent extracts this pool of
trapped hot air making the room far cooler and actually cooling the ceiling
plaster. This means not requiring an expensive needless a/c.

Victorian houses had high ceilings to take the fumes of gas lights. With
Georgian windows up to ceiling level you can pull down the top sash for
effective cooling.

Most people don't understand any of and go out and buy expensive a/c
equipment. Understand nature and go with it.



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