Solar Heat Gain Coefficient Requirements of Glass on Façade for meeting the GRIHA Compliance
Solar Heat Gain Coefficient (SHGC) is the amount of solar radiation that transmits through a window in the form of heat via three forms of thermodynamic heat transfer, i.e., conduction, convection, and radiation. the coefficient is expressed as a value between 0 and 1. the lower the SHGC, the lower the potential for heat transfer.
For meeting the GRIHA compliance, the Solar Heat Gain Coefficient (SHGC) requirements of glass on the façade are based on the ECBC 2007 (Energy Conservation Building Code) standards. The ECBC 2007 provides guidelines for the maximum SHGC values for glass on different orientations of the building envelope to reduce the solar heat gain through the building’s glazing system.
As per the GRIHA V 2015 criteria 11.1.2, all fenestration should meet the SHGC requirements of ECBC 2007, or the weighted façade average SHGC (for each orientation) should meet the SHGC requirements of ECBC 2007.
Steps to Calculate effective SHGC (SHGCeff):
In order to calculate SHGCeff , first the projection factor (PF) needs to be calculated for the shaded window. PF is the ratio of the length of projection ‘H’ (shade such as an overhang or louver) to the height from window sill up to the bottom of the shade ‘V’.
If the PF falls within 0.25 and 1, the PF is used to calculate the M-factor (taken from ECBC table 4.4) based on project location and orientation. The SHGCeff is obtained by multiplying the SHGC of glass with the M-factor.
To meet the GRIHA compliance, the SHGC value of the glass used in the façade should not exceed the values mentioned above. It’s important to note that this is just one aspect of the daylight compliance requirements of GRIHA, and additional criteria must also be met to achieve compliance.