A7 Passive Solar Design

Topic

Passive solar design leverages the sun's position in the sky to heat a building in winter and shield it from that same sun in summer—achieving this through the building's geometry rather than mechanical systems. The sun's altitude above the horizon varies throughout the day and year depending on the location's latitude; it is precisely this seasonal difference—a high sun in summer and a low sun in winter—that allows for the design of window overhangs or eaves calculated to block the high summer sun while admitting the low winter sun, thereby providing shade when heat is unwanted and solar gain when it is desired.

The total radiation striking a façade is the result of three components determined by the surface's orientation and tilt: direct solar radiation, diffuse radiation scattered by the sky, and radiation reflected from the immediate surroundings.

The ratio of glazed area to total façade area is also a passive solar design decision, not merely an aesthetic one: more glass captures both more light and more solar heat—reinforcing the concept of solar gain discussed in the window module—so this ratio must be adjusted according to the climate and the specific orientation of each façade.

Thus, this module—which begins by addressing the sun's altitude as it changes with the seasons—concludes by demonstrating that passive solar design does not aim to simply maximize or minimize solar radiation in absolute terms; rather, it seeks to capitalize on the changing solar altitude to admit sunlight when beneficial and block it when it is not.

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