What are the red and blue arcs on the annual sun-path?

When you overlay an Annual Sun-Path Diagram on the model in the VISUALISE page, two additional red and blue arcs appear that are not displayed in any of the other Sun-Path diagram views. What do they show?

These arcs represent the range of azimuth angles that the Sun travels through in Summer and Winter. The aim in showing these arcs is to highlight the seasonal differences and allow the designer to quickly understand and, hopefully, take advantage of them.

Figure 1 - An example of the red and blue arcs displayed when a sun-path diagram is overlaid in the VISUALISE page.

Figure 1 - An example of the red and blue arcs displayed when a sun-path diagram is overlaid in the VISUALISE page.

The red arc represents the range from sunrise to sunset on the day of the Winter Solstice. In many climates, this is a period where solar heating is desirable, so the red arc represents those areas of the facade that have the potential to collect incident solar radiation for this purpose.

The blue arc represents the range from sunrise to sunset on the day of the Summer Solstice. In many climates this, is a period when solar heating is definitely unwanted, so the blue arc represents those areas of the building facade and its apertures that may need protection against incident solar radiation.

Figure 2 - Each arc represents the range of azimuth angles traversed by the Sun on the Summer and Winter Solstices.

Figure 2 - Each arc represents the range of azimuth angles traversed by the Sun on the Summer and Winter Solstices.

Interpretation

The things to look for with this display are:

  • The further your location from the equator, the greater the difference in the range of azimuth angles covered in each season.
  • In all but equatorial climates, the range of Sun azimuth angles in Summer is greater than in Winter.
  • Typically, by the time the Sun in Summer passes over the range of azimuth angles in Winter, it is much higher in the sky.
  • Thus, careful design of the shape of shading devices over a window can allow you to provide complete protection in Summer whilst allowing reasonable solar collection in Winter.



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