What is the difference between SHGC & SC of a glass?
SHGC and Shading coefficient are both terms used for fenestration of a building. They are used to describe properties of a glass while determine solar heat gain through a window.
Solar Heat Gain Coefficient (SHGC)
The Solar Heat Gain Coefficient (SHGC) is the percent of solar energy incident on the glass that is transferred indoors both directly and indirectly through the glass. The direct gain portion is the solar energy transmittance, while the indirect is the fraction of solar energy incident on the glass that is absorbed and re-radiated or transmitted through convection indoors.
Shading Coefficient (SC)
The Shading Coefficient (SC) is a measure of the heat gain through glass from solar radiation. Specifically, the Shading Coefficient is the ratio between the solar heat gain for a particular type of glass and that of double-strength clear glass. A lower Shading Coefficient indicates lower solar heat gain.
Relationship between SC and SHGC
SHGC is a newer term used for SC. SHGC is a more comprehensive term when it comes to solar radiation gain through glass. ASHRAE 90.1-13 Section 5.8.2.4 Exception 1 states:
“Shading coefficient (SC) of the
center-of-glass multiplied by 0.86 shall be an acceptable alternative
for determining compliance with the SHGC requirements for the overall
fenestration area. SC shall be determined using a spectral data file
determined in accordance with NFRC 300. SC shall be verified and
certified by the manufacturer.”
SHGC & SC requirements for ECBC compliance
SHGC shall be determined for the overall single or multi glazed fenestration product (including the sash and frame) in accordance with ISO-15099 by an accredited independent laboratory, and labeled or certified by the manufacturer.
Exceptions :
(a) Shading coefficient (SC) of the center of glass alone multiplied by 0.86 is an acceptable alternate for compliance with the SHGC requirements for the overall fenestration area.
(b) Solar heat gain coefficient (SHGC) of the glass alone is an acceptable alternate for compliance with the SHGC requirements for the overall fenestration product.