Building Orientation

Solar Radiation in Various Directions

The building orientation determines the amount of radiation it receives. If the variations of solar radiation intensities on a horizontal surface and the vertical walls of different orientations are graphically compared, the following facts will be apparent:

  1. In most equatorial and tropical locations, but especially near the Equator. The horizontal surface receives the greatest intensity.
  2. At the higher latitude, the wall facing the Equator receives the next highest intensity in winter (when the Sun is low) but it receives very little in summer.
  3. In the equatorial location, north and south walls receive the least intensity and that only for short periods of the year.
  4. East and west facing walls receive the second highest intensities in the equatorial location and consistently large intensities even at the higher latitude.
In the equatorial location, if solar heat gain is to be avoided, the main windows should face north or south. At the higher latitude, an orientation away from the Equator would receive the least sunshine, but here it may be desirable to have some solar heat gain in winter, when the sun is low- so an orientation towards the Equator may be preferable. In both locations, only minor openings of unimportant rooms should be placed on the east and west side. Solar heat gain on the west side can be particularly troublesome as its maximum intensity coincides with the hottest part of the day.

Solar heat gains per square meter of the wall area of the east and west facades at the latitude of 28 degree N (latitude of New Delhi) are given in the table below.

June 21 6 7 8 9 10 11 12 am - East facing
6 5 4 3 2 1 -- pm - West facing
Heat gain 1.24 2.2 2.4 2.2 1.66 0.94 0.5 MJ/m2
Solar elevation angle 11 23 36 49 63 76 85 Degree
December 21 6 7 8 9 10 11 12 am - East facing
6 5 4 3 2 1 -- pm - West facing
Heat gain 0 0.12 1.84 2.02 1.56 0.78 0.29 MJ/m2
Solar elevation angle - 1 13 23 31 37 39 Degree

It can be seen that significant heat gain occurs between 0600 hrs to 1000 hrs on east walls, and between 1400 hrs to 1800 hrs on west walls when the sun is lower in the sky. The east and wets windows are therefore, sources of solar heat gain and should therefore either be eliminated or reduced in size. It is also advised to place unconditioned spaces (garages, closets and other buffer places) in the east and west sides. Orientation for taking advantage of breezes in warm and humid climate and for prevention of hot winds in hot and dry climates is important but not as critical as orientation for solar heat control.

Imagine a 1m cube oriented such that each surface faces in the four cardinal directions, north, south, east and west. If we were to measure and graph the amount of incident solar radiation on each surface on a hot summer's day, and compare that to the total available radiation, we would get the following graphs. These were generated for a mid-latitude (30° latitude) climate in midsummer, using recorded hourly weather data.

Graphs of hourly incident solar radiation on surfaces at different orientations on a summer day at mid-latitudes

There are a number of interesting points contained within these graphs.