The correction factor for the glazing/blind combination, fc, may either be selected from Table 13.2, or obtained from the appropriate shading coefficients. The shading coefficients for various glazing and shading device combinations
Table 13.2 Correction factor for glazing/blind combinations.
Glazing/blind combination (from inside to outside)
Correction factor fc
0.95 0.62 0.66 0.92 0.60 0.62 0.69 0.47 0.50 0.56 0.37 0.39 0.57 0.47
Blind/clear/reflecting Blind/clear/absorbing Blind/low-e/clear
Blind/low-e/reflecting Blind/low-e/absorbing Clear/blind/clear
Clear/blind/reflecting Clear/blind/absorbing Clear/clear/blind/clear
Clear/clear/blind/reflecting Clear/clear/blind/absorbing Clear/clear/blind Clear/clear/clear/blind are often provided by manufacturers. For the purposes of Appendix H they are defined as:
Sc The ratio of the instantaneous solar heat gain through the glazing and its shading device at normal incidence to the instantaneous solar heat gain through clear unshaded 4 mm glass. Scf As Sc, but for glazing with a fixed shading device. Sctot As Sc, but for glazing with fixed and moveable shading devices.
There are three equations which relate these shading coefficients to the correction fc:
• For fixed shading, including units with absorbing or reflecting glass:
• For moveable shading:
• For a combination of fixed and moveable shading:
These equations maybe used to find fc, or they may be inverted in order to determine the shading coefficient, and hence the glazing/shading device combination, which is required to meet the 25 W/m2 criterion.
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