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re: heat loss through skylight
28 dec 2005
m ransley wrote:
>if it could automaticly close with a foam insulating plug when shaded
>it could be a net gain.
that's better, but any skylight is a net gain if more solar energy enters
during a day than heat energy leaves during a day, which can happen with
several layers of glazing. for instance, 3 layers of r1 glazing with 90%
solar transmission would gain 0.9x0.9x0.9x460 = 335 btu/ft^2 and lose
24h(65-26.7)1ft^2/r3 = 306, for a net gain of 29 btu/ft^2 on an average
december day in chicago.
by contrast, insulation just loses heat. an r100 ceiling would just lose
24h(65-26.7)1ft^2/r100 = 9 btu/ft^2.
would you rather gain 29 or lose 9 btu of heat per day in december?
nick
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