Sunworshipper wrote: (clip) Can anyone explain how radiant barriers are
effective on buildings or maybe suggest another group to ask? (clip)
^^^^^^^^^^^^^^^^^
There is radiation of energy from ANY surface, proportional to the 4th power
of the absolute temperature. The transfer between two surfaces is going to
be proportional to the DIFFERENCE in the 4th powers, affected also by other
parameters, INCLUDING the emissivity of the surfaces. Shiny aluminum has a
low emissivity, so it cuts down the radiant transfer. This has nothing to
do with the fact that the outside of the building is being heated by
sunlight. That sun's energy is converted to thermal energy in the plywood,
concrete or whatever else the walls are made of(raises their temperature) ,
and it travels into the wall by conduction. The inner surfaces of the wall
get warmer as a result, which then transmit some of the energy to other
inner surfaces by radiation. Introducing a reflective radiation shield
within an air space sends most of the radiation back the way it came, thus
reducing the heating inside the room.

So aluminum foil can work in two ways: 1.) If it is adhered to a surface,
it lowers the emissivity. If it is suspended in an air gap, it reflects
energy back toward the source.