Page 23 - GRIHA Manual Volume III - Introduction to National Rating System
P. 23
16 GRIHA Manual: Volume 3
Conclusion: The primary objective of shading is to reduce heat gain and glare due to direct insolation.
However, the design of the shading device should be such that it can allow required daylight
for the respective internal spaces (as recommended in GRIHA criterion 13 table 13.2). Therefore,
shading design is optimized on the basis of reduction of incident heat gain as well as provision of
adequate daylight.
5. Sizing of openings
Glazing allows shortwave infrared radiation emitted by the sun to pass through, but is almost opaque
to longwave radiation emitted by objects in the room. The consequence is that once the radiant
heat has entered through a window, it is trapped inside the building, a phenomenon called the
‘green house effect’. Hence, the heat gain in buildings can be reduced by limiting the glazing area.
Windows, typically, have a higher conductance coefficient than the rest of the building envelope so
that buildings with high glazing areas will have greater heat gain, as compared to similar buildings
with lesser glazing area. Therefore, GRIHA has limited the glazing area especially for the hot regions
of India in terms of window-to-wall ratio (WWR) and skylight-roof-ratio (SRR).
a. Window-to-wall ratio
Window-to-wall ratio (WWR) is the ratio of vertical fenestration area to gross exterior wall area. Gross
exterior wall area is measured horizontally from the exterior surface; it is measured vertically from
the top of the floor to the bottom of the roof. (Source Energy Conservation Building Code 2007)
Net glazing area
WWR = ________________________
Gross exterior wall area
Gross wall area: The overall area of a wall including openings such as windows and doors measured
horizontally from outside surface to outside surface, and measured vertically from the top of the
floor to the top of the roof. If roof insulation is installed at the ceiling level rather than the roof,
then the vertical measurement is made till the top of the ceiling. The gross wall area includes the
area between the ceiling and the floor for multi-storeyed buildings. (Source Energy Conservation
Building Code 2007)
b. Skylight-roof-ratio
The ratio of the total skylight area of the roof, measured from the outside of the frame to the gross
exterior roof. (Source ECBC)
Net glazing area
SRR = ________________________
Gross exterior roof area
Gross exterior roof: The area of the roof measured from the exterior faces of walls or from the centre
line of party walls.
Example: In the building shown below, if the total window area = 6035 m and total opaque wall
2
area = 4885 m , then what is the WWR of the building?
2
WWR = 6035/ (6035+4885) x 100 = 55%
Conclusion: The primary objective of shading is to reduce heat gain and glare due to direct insolation.
However, the design of the shading device should be such that it can allow required daylight
for the respective internal spaces (as recommended in GRIHA criterion 13 table 13.2). Therefore,
shading design is optimized on the basis of reduction of incident heat gain as well as provision of
adequate daylight.
5. Sizing of openings
Glazing allows shortwave infrared radiation emitted by the sun to pass through, but is almost opaque
to longwave radiation emitted by objects in the room. The consequence is that once the radiant
heat has entered through a window, it is trapped inside the building, a phenomenon called the
‘green house effect’. Hence, the heat gain in buildings can be reduced by limiting the glazing area.
Windows, typically, have a higher conductance coefficient than the rest of the building envelope so
that buildings with high glazing areas will have greater heat gain, as compared to similar buildings
with lesser glazing area. Therefore, GRIHA has limited the glazing area especially for the hot regions
of India in terms of window-to-wall ratio (WWR) and skylight-roof-ratio (SRR).
a. Window-to-wall ratio
Window-to-wall ratio (WWR) is the ratio of vertical fenestration area to gross exterior wall area. Gross
exterior wall area is measured horizontally from the exterior surface; it is measured vertically from
the top of the floor to the bottom of the roof. (Source Energy Conservation Building Code 2007)
Net glazing area
WWR = ________________________
Gross exterior wall area
Gross wall area: The overall area of a wall including openings such as windows and doors measured
horizontally from outside surface to outside surface, and measured vertically from the top of the
floor to the top of the roof. If roof insulation is installed at the ceiling level rather than the roof,
then the vertical measurement is made till the top of the ceiling. The gross wall area includes the
area between the ceiling and the floor for multi-storeyed buildings. (Source Energy Conservation
Building Code 2007)
b. Skylight-roof-ratio
The ratio of the total skylight area of the roof, measured from the outside of the frame to the gross
exterior roof. (Source ECBC)
Net glazing area
SRR = ________________________
Gross exterior roof area
Gross exterior roof: The area of the roof measured from the exterior faces of walls or from the centre
line of party walls.
Example: In the building shown below, if the total window area = 6035 m and total opaque wall
2
area = 4885 m , then what is the WWR of the building?
2
WWR = 6035/ (6035+4885) x 100 = 55%
