A passive system has no moving parts other than motorized shades or insulation barriers
to prevent heat loss at night through the glazing.
The most common passive system consists
of a large room that resembles half of a green house with a wall of glass or other transparency
facing due south or north (dependent on the building location in respect to the equator) to prevent infiltration of outside air. The solar radiation becomes heat energy as it passes
through the glazing and strikes the storage medium. A wall of concrete, a floor of concrete
or stone, or large vertical cylinders filled with water are used to store the heat. At night,
as the temperature of the home drops, doors between the storage room and the house are opened
so the warmth that has been stored will radiate into the air and temper the home. Insulated
shades or blankets covering the glazing during the night will keep external heat loss to
a minimum.
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