Why use Reflector/Shades?

In winter buildings need heat gain without heat loss.  A reflector that adds 30% to energy incedent on the south glass is of more benefit than a 30% larger window. The reflector’s light gets in free since existing heat losses are not affected by the added radiation which is pure profit.  Windows with low “e” glass and high R values benefit from reflectors just as others do.  Horizontal skylights long in the e-w direction and narrow from north to south are perfect for reflector/shades.  Their gain during sunny winter weather can be more than doubled, thus increased above that of optimally placed sloped glazing.

These are winter advantages of reflector shades; those in summer are equally great.  South facing glass that is not essential for a view or for daylight such as used in front of Trombe walls or drum walls can overheat buildings even if overhangs shade most of the glass at the summer solstice.  Glare from the ground and diffuse daylight through such glass adds a great deal of unwanted heat during the summer (500 to 600 Btu’s/sq.ft. day).  The most efficient way to block this is with the same device that added gain in winter, a reflector/shade. Unfortunately a Trombe wall, without a reflector/shade can add as much heat that we don’t want in July as it does heat that we do want in December.

Horizontal skylights, even just a few percent of the floor area, become a great problem in summer when they overheat the rooms below them. Skylights without shades are like cars without brakes. Reflector/shades, lowered in the summer can keep out all direct sun, yet let in daylight during the hot time of year.