PÉCLETBuilding Physics
PÉCLET / Disciplines / 02G — W/m² · SHGC — 0…1

Solar

The sun is the largest thermal event in the life of a building, and it arrives on a schedule you can calculate.

QuantityIrradianceTransportShortwave radiationInteractionDrag horizontally to move through the day. Drag vertically to move through the year.
Fig. 02 — Sun path and shadowDrag: sideways for time of day, up and down for month
At latitude 28.6 degrees north in June at 10:00 solar time, the sun sits at an altitude of 62.5 degrees and an azimuth of -85.4 degrees from south. The building casts a shadow across the ground.
Altitude62.5°Azimuth-85.4°Day length13.8 h
Sun above horizonAzimuth measured from south, positive west
A simple building mass on a ground plane, seen in three dimensions. The sun travels along an arc overhead, and the building casts a shadow that lengthens, rotates and shortens as the sun moves. Façades brighten as they come into direct sun and fall dark as they pass into shade, with a readout of solar altitude and azimuth.

The position

Solar gain is neither good nor bad. In January it is the cheapest heating a building will ever receive; in May it is the load that sizes the plant. The geometry of the year decides which one you get.

Orientation, shading depth, glazing ratio and glass specification are a single connected decision. We work them together, early, while they are still cheap to change.

What we ask

  • 01When does each façade actually see the sun, and for how long?
  • 02What does the overhang do in June that it does not do in December?
  • 03Is glare being solved, or simply moved to another room?
  • 04Which façade is sizing the cooling plant?

How we answer it

  • 01Annual sun-path and shading studies
  • 02Façade-by-facade irradiance assessment
  • 03Shading device geometry development
  • 04Glazing specification and glazing ratio testing