solar-chart by M. HUMAM

1. Solar Chart & Design of Shading
Devices

2. Sun Path Diagrams
• Sun-path diagrams or solar charts are the
simplest practical tools for depicting the sun’s
apparent movement.
• The sky hemisphere is represented by a circle
(the horizon).
• Azimuth angles (i.e. the direction of the sun) are
given along the perimeter and
• Altitude angles (from the horizon up) are shown
by a series of concentric circles, 90◦ (the zenith)
being the centre.

8. • The sun-path lines are plotted on this chart for a given
latitude for the solstice days, for the equinoxes and for any
intermediate dates.
• For an equatorial location (LAT = 0◦) the diagram will be
symmetrical about the equinox sun-path, which is a straight
line; for higher latitudes the sun-path lines will shift away
from the equator.
• For a polar position the sun-paths will be concentric circles (or
rather an up and down spiral) for half the year, the equinox
path being the horizon circle, and for the other half of the
year the sun will be below the horizon.
• The shifting of sun-paths with geographical latitudes is
illustrated by the following Figures.
• The date-lines (sun-path lines) are intersected by hour lines.
• The vertical line at the centre is noon.

11. • Use a Sun Path Diagram to find solar altitude and
azimuth for any given time, to help in sizing
shading devices.
• Choose the sun path diagram with latitude
closest to your site.
• Find the intersection of the two curves
corresponding to the month and hour of interest.
• From this point, read solar altitude from scale at
right and read solar azimuth from scale below.
• This is the sun’s position at that month and hour.

14. SHADING DEVICES
1. Vertical devices, e.g. vertical louvres or projecting fins.
• These are characterised by horizontal shadow angles (HSA) and
their shading mask will be of a sectoral shape.
• By convention HSA is measured from the direction of orientation
(i.e. From the surface normal), positive in clockwise and negative in
the anticlockwise direction.
• The HSA cannot be greater than 90◦ or less than −90◦, as that would
indicate that the sun is behind the building.
• These devices may be symmetrical, with identical performance
from left and right, or asymmetrical.
• They are most effective when the sun is towards one side of the
direction the window is facing.
• We may distinguish the ‘device HSA’ (as above) and the ‘solar HSA’,
which is the required performance at a given time.

16. 2. Horizontal devices, e.g. projecting eaves, a horizontal canopy or
awning, or horizontal louvers and slats.
• These are characterized by a vertical shadow angle (VSA).
• One large or several small elements may give the same
performance, the same vertical shadow angle.
• Their shading mask, constructed by using the shadow angle
protractor , will be of a segmental shape.
• They are most effective when the sun is near-opposite to the
window considered.
• Figure shows a canopy with a ‘device VSA’ of 60◦.
• The ‘solar VSA’ is the same as the ALT (altitude) only when the sun
is directly opposite the window (when AZI = ORI, or solar HSA = 0).
• When the sun is to one side of the surface normal, its altitude must
be projected onto a vertical plane perpendicular to the window.

19. • Egg-crate devices, e.g. concrete grille-blocks, metal grilles.
• These produce complex shading masks, combinations of the
above two and cannot be characterized by a single angle.
• An example of this is shown in Figure.

21. Sizing Overhangs and Fins
• Use these equations to find starting dimensions for shading
elements. Do the calculations to find:
– depth required for a shading element, or
– extent of shadow cast by a shading element with given depth.
• For each facade, select a critical month and time for
shading.
• Suggested: south windows use September noon, east use
September 10 am, west use September 3 pm, or ask
mechanical engineer for estimate of peak cooling time in
east, south, and west zones.
• Find solar altitude and azimuth for target month/hour from
the sun path diagrams.

22. • Use the formulas below to size overhang, fin, or both.
Results are a minimum starting point.
• If overhang is too big, try breaking it into several smaller
elements or dropping part of it down for an equivalent
depth.
• If sizing overhang for east or west window, you may notice
that a fin must be added for adequate shading; otherwise
overhang becomes unreasonably deep.
• Improvements: Extend ends of overhang wider than
window or use a continuous element. Make overhang
deeper or add another horizontal element part-way down
the window. Add vertical elements to the scheme.