APPENDIX III.1 EFFECT OF SHADING DEVICES The heat gain through windows has a major role in controlling the indoor temperatures in case of non-conditioned buildings and heating and cooling load in case of conditioned buildings. It is therefore necessary to examine the effect of various chajja-fin combinations to reduce the heat gain. For this purpose the amount of direct solar radiation incident on windows has been considered as the basis. The effect of size of chajja, fin, gap, extension and windows in the four cardinal directions (i.e. north, east, south and west) has been studied. These terms are defined as follows: Fin/Chajja depth:
Projection outward from the wall,. (When a chajja is assumed to have a depth of say X meters, all the fins are also assumed to have a depth of X meters. The chajja and fin meet at an edge at top) Fin length : Length measured from the top edge of the window to the bottom of the fin. (Four cases considered are: no fin, fin upto one third of window height measured downwards from top edge of window, fin upto two third of window height measured downwards from top edge of window and fin upto window height measured downwards from top edge of window). Gap
:
Extension
:
The distance between the top edge of window and the chajja The distance between the left or right fin to the nearest vertical edge of window. In case there is no fin, it is the length by which the chajja extends beyond the width of the window.(Extension is assumed equal on both sides of the window)
Figure III.1 illustrates these terms graphically. The various cases considered are: Window size
:
0.6 x 1.2 , 0.6 x 1.8, 1.2 x 1.2, 1.2 x 1.8, 1.8 x 1.2, 1.8 x 1.8 (m2)
Fin/Chajja depth
:
0.0, 0.3, 0.6, 1.0 (m)
Fin length
: : : :
No fin, Upto 1/3 of window height measured from top. Upto 2/3 of window height measured from top. Equal to the window height.
Gap
:
0.0, 0.15(m)
Extension
:
0.0, 0.15(m)
Windows are given a set back of 0.1 m from the exterior surface of the wall. Beam radiation incident on the window per unit area ( i.e., Beam radiation on window X (Window area - Shaded area) / Window area) is found out for the hours between 9 a.m. to 4 p.m. (IST) for all days of the year. This particular time span has been chosen to avoid the absurd values, which may crop in due to the low magnitudes of the trigonometric functions for hours before 9 a.m. and after 4 p.m. It may be mentioned that the intensities of solar radiation before 9 am and after 4 p.m. are generally small. So the assumption does not lead to significant error. Further, this calculation