different forms of sun-path diagrams and their uses in functional design of buildings

1. DIFFERENT FORMS OF SUNPATH DIAGRAM
AND THEIR USES IN FUNCTIONAL DESIGN
OF BUILDINGS
K K SRIRAM
CE14B026

2. Not “sun-bath” its “Sun-path”

3. Definition-layman’s terms.
• Sun path refers to the apparent significant
seasonal-and-hourly positional changes of the
sun (and length of daylight) as
the Earth rotates, and orbits around the sun.
• Sun-path diagram as the name suggests is
something that is used to determine the
location ,in the sky, of the sun at any point of
time during the day, throughout the year.

4. Use in Functional Design
The most immediate use of a sun-path
diagram is that the solar azimuth and the
altitude can be read and hence the position
can be exactly determined..
• The optimum position and orientation of
various sunlight related equipment like solar
heaters, ovens is known.

5. • By studying the sun-path diagram of a place
one can identify the optimal orientation of
solar panels in a given building.

6. • By identifying the solar-windows of a
particular location, one can design the
building such that there is maximum utility of
the solar energy by placing thermal mass
required for indirect heat gain in the right
orientation.

7. • By tracing down the surface area illuminated,
to the greatest extent, by the sun, the location
of clerestories and fenestrations of a building
can be optimised so that the thermal and
visual comfort levels in the building are met.
• The shading devices also can be designed
similarly.

8. • Coming to one of the most important uses, the location of the
house so that it receives the maximum shade during summer
can be obtained using softwares like autodesk ecotect

9. Different forms
• For all those who are wondering how a
sunpath diagram looks like…

10. • Wait, this is the 3-D view, how does this look
like on paper?
• So people came up with methods to represent
it on paper which define the basis for
characterization of sun-path diagrams.
• The most popular 2 representations are:
polar and cartesian.

11. Polar sun-path diagrams

12. What is a polar sun-path diagram??
• Imagine somebody lying on the ground facing
the sky and starts taking photographs of the
sky all along the day, throughout the year
using a fish lens camera.
• All these photographs superimposed forms a
polar sun-path diagram.

13. How does somebody even read that?
• Azimuthal lines:
Azimuth angles run around the edge of the diagram in 15° increments. A
point's azimuth from the reference position is measured in a clockwise
direction from True North on the horizontal plane. True North on the
stereographic diagram is the positive Y axis (straight up) and is marked with
an N.
• Altitude lines:
Altitude angles are represented as concentric circular dotted lines that
run from the centre of the diagram out, in 10° increments from 90° to
0°. A point's altitude from the reference position is measured from the
horizontal plane up.

14. • Date and month lines:
Date lines represent the path of the sun through the sky on one particular day of
the year. They start on the eastern side of the graph and run to the western side.
There are twelve of these lines shown, for the 1st day of each month. The first six
months are shown as solid lines (Jan-Jun) whilst the last six months are shown as
dotted (Jul-Dec), to allow a clear distinction even though the path of the Sun is
cyclical.
• Hour Lines:
Hour lines represent the position of the sun at a specific hour of the day,
throughout the year. They are shown as figure-8 style lines that intersect the date
lines. The intersection points between date and hour lines gives the position of the
sun. Half of each hour line is shown as dotted, to indicate that this is during the
latter six months of the year.

15. • Step 1 - Locate the required hour line on the diagram.
• Step 2 - Locate the required date line, remembering that solid are used for Jan-
Jun and dotted lines for Jul-Dec.
• Step 3 - Find the intersection point of the hour and date lines. Remember to
intersect solid with solid and dotted with dotted lines.
• Step 4 - Draw a line from the very centre of the diagram, through the intersection
point, out to the perimeter of the diagram.
• Step 5 - Read the azimuth as an angle taken clockwise from North.
• Step 6 - Trace a concentric circle around from the intersection point to the
vertical North axis, on which is displayed the altitude angles.
• Step 7 - Interpolate between the concentric circle lines to find the altitude.

16. Classification of Polar representation
• Depending on the scale of the altitude circles,
the projections are again classified into 3
types:
Spherical , Equidistant and Stereographic.

18. Spherical projection
• In this method, the radial distance from the centre is simply the cosine of the altitude
angle. As shown above, the relative change in radius between 75° and 90° is very much
greater than between 15° and 0°.
• Uses : This makes such diagrams very good for considering overhead shading or very tall
surrounding buildings.

19. Equidistant projection
• Using this method the radial distance is simply a linear factor of the altitude angle. Thus
the relative change in radius between all angles is the same.
• Uses: There is no bias towards either the zenith or the horizon.

20. Stereographic projection
• This is a more complex projection in which azimuth lines are first projected back to a
reference point located a distance of 1 radius beneath the circle centre. The point
where each of these lines intersects the zero axis gives the radial distance.
• Uses: The primary advantage of this method is that it increases the resolution of the
diagram at low solar altitudes making it more suitable for the majority of surrounding
building overshadowing situations.

21. Cartesian sun-path diagram

22. • Similar to the polar sun-path diagrams,
somebody takes pictures of the sky and starts
collecting the data regarding the position of
the sun quantized by the azimuthal and
altitude of the sun.
• Now the azimuthal values are plotted along
the X-axis and the altitude values are plotted
along the Y-axis for different parts of the day
and throughout the year.

23. Reading the cartesian sun-path diagrams.
• Step 1 - Locate the required hour line on the diagram (similar to that in polar).
• Step 2 - Locate the required date line, remembering that solid are used for Jan-Jun and
dotted lines for Jul-Dec. In these diagrams, the highest altitude line at noon is always in
midsummer (either 1st July or 1st Jan, depending on hemisphere). Each other line
represents the 1st of each month, solid Jan-Jun, dotted Jul-Dec.
• Step 3 - Find the intersection point of the hour and date lines. Remember to intersect
solid with solid and dotted with dotted lines.
• Step 4 - The azimuth is given by reading off the horizontal axis.
• Step 5 - The altitude is given by reading off the vertical axis.

25. Classification of cartesian representation
• Not all parts of the sky contribute equally to the daylight that arrives at a surface or passes through
a window. Different sky conditions can result in variations in the distribution of luminance over the
sky dome, with some areas brighter or darker than others. For a flat surface or a window, light
from some parts of the sky will arrive at normal incidence whilst others will arrive at almost grazing
incidence, with the cosine law determining their relative contribution.
• These effects can be accommodated within cartesian sun-path diagrams by applying non-linear
scales to one or both of the axis. This can be done solely for visualization purposes or, with the
addition of distributed points or a grid of squares, used as a basis for manually taking off
measurements for day-lighting potential or overshadowing effect.
• Those well modified implemented diagrams are called Waldram diagrams.

27. Thank you.