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radiant heat

Posted by Bill Stout on June 21st, 2000 10:17 PM
In reply to Made in the shade... by Dodgeman on June 21st, 2000 12:50 PM [Go to top of thread]

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Radiant heat does not depend upon conduction to be transimitted. A simple proof is standing in front of a bonfire when it is 30 degrees ouside. Your face will be burning while your butt is freezing. Place a simple shield (even your hand in front of your face and you immediately block the radiant transfer and yor face gets cold. When the sun hits the roof it gets hot and then becomes a"secondary radiant transimitter" Any object, regardless of its tempertature will radiate heat (even if its 100 degrees below zero) the transmission of it's heat is dependant upon the surrounding objects temp (if an object is warmer than the -100 degrees it will give up some heat to the colder object). ie. your roof can easily approach 150 degrees temp on the immediate surface (within the first few millimeters of depth). of course this temp is immediately "conducted" through the roof. the underside of the roof can hit 130 degrees or more depending on the ambient conditions. This then becomes a 130 degree radiator which then heats the floor of your attic and ultimately your house. Of course the efficency is dependant upon the actual "Delta t" (the temp gradient across your insulation) with the mirror (radiant paint) a large portion of the radiant heat is reflected back through the roof and into the atmosphere. Sorry about the long winded explanation, but thermodynamics is a very complex subject. Any more questions, I'll try to answer.

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