Daylighting Design Overlays for Equidistant Sun-Path Projections

Projections of the suns daily and seasonal paths frequently are used to solve building design problems involving site obstructions and shading of fenestration. In the United States, equidistant projections are perhaps the most widely used (compared to other sunpath projections) because of the commercial availability of a complete set of sun-path diagrams for a range of useful latitudes.

This paper describes the development of a set of overlays designed for use with sun-path projections to predict illumination on any building surface throughout the year for standard climatological conditions. Illumination is calculated for clear and overcast skies and for direct sunlight using algorithms recommended by the CIE. Values for illumination incident upon the surface, as well as transmitted through single and double glazing, can be calculated. Similar overlays for solar radiation are being developed.

With these overlays, a sun-path diagram becomes a more versatile and powerful design tool for solving a wide range of siting, sun control, thermal transfer, and daylighting problems.