I have 8, 4ft x 7 ft windows in my passive solar house. I want to use a radiant barrier in a blind to reduce the heat loss from each window on winter nights. What is the optimum spacing between the inner side of the double panned window glass and a double-sided reflective membrane? What is the optimum spacing between the first sheet and a second reflective membrane? What is the best reflective, (on both sides), material to use for this purpose? I recall a membrane called “mylar” years ago. What is the incremental benefit from a second membrane? What is the incremental benefit from a third membrane? I prefer “occupant comfort” to energy conservation, both would be best. Given that thermal comfort is a function of the difference between heat radiated by the body, and radiant heat received by the body, would a high emissivity coating be better on the interior surface than a shiny, low emissivity surface? Are you aware of any manufacturers of blinds like that described above?
A single layer of radiant barrier is sufficient to block the radiant heat waves from entering through the windows. Aluminum foil blocks 97% of the heat, so additional layers would not provide any significant benefit. Also, a reflective surface facing another reflective surface will offer no benefit. The minimum spacing between the window and the radiant barrier would be 3/4″. Allow for air flow around the sides and at the bottom. There are several companies that make low-e blinds — you should be able to find them on the web.