Passive solar building design involves the modeling, selection and use of appropriate passive solar technologies to maintain the building environment at a desired temperature range (usually based around human thermal comfort) throughout the sun's daily and annual cycles. As a result it generally minimizes the use of active solar, renewable energy and especially fossil fuel technologies.

Passive solar building design is only one part of thermally efficient building design, which in turn is only one part of sustainable design, although the terms are often used erroneously as synonyms (passive solar design does not relate to factors such as ventilation, evaporative cooling, or life cycle analysis unless these operate solely by the sun).

Key concepts There are three basic passive solar energy strategies: direct solar gain, indirect solar gain, and isolated solar gain.

Direct solar gain
Direct gain involves using the positioning of windows, skylights and shutters to control the amount of direct solar radiation reaching the interior spaces themselves, and to warm the air and surfaces within the building. The use of sun-facing windows and a high-mass floor is a short-cycle example of this. John Hait's "Passive Annual Heat Storage" (PAHS) method is an example of an annualized solar approach primarily using this path.

Direct solar gain systems were initially challenged as historically there were no reasonably priced transparent thermally insulating materials with R-values comparable to standard wall insulation. This has changed with the advent of high R-value windows and window shades, especially in Europe where superinsulated windows have been developed and are widely used to help meet the German Passive House standard.

In the northern hemisphere, a design that uses too much south-facing glass can result in excessive heating and an uncomfortably bright living space at certain times of the year. Conversely, in the southern hemisphere the same is true for north-facing glass.

Next Page: Indirect/Isolated Solar Gain