Glossary:Glossary-Plus

Glossary: WUFI-Plus

Solar Heat Gain Coefficient

• The Solar Heat Gain Coefficient (SHGC) measures how well a window blocks heat from sunlight. The SHGC is the fraction of the heat from the sun that enters through a window, both directly transmitted, and absorbed and subsequently released inward.
• The SHGC replaced the shading coefficient an the standard indicator of a window‘s shading ability
• SHGC is expressed as a number between 0 and 1.
• SHGC can be expressed in terms of the glass alone or can refer to the entire window assembly.
• The lower a window's SHGC, the less solar heat it transmits.
• For incident radiation that is diffuse, the hemispherical SHGC must be used.

[[1]] [[2]] ASHRAE Handbook 2005 Fundamentals

g-Value

The g-value is a value for the pass of energy through a transparent component. It is composed of direct solar radiation and heat emission by secondary absorptance to the inner space.

$g={\tau }_e+q_i[1]$

The radiation power \phi_e through the component can be separated as following:

transmitted part \tau_e \phi_e direct transmittance \tau_e
reflected part \rho_e\phi_e direct reflectance \rho_e
absorbed part \alpha_e \phi_e direct absorptance \alpha_e [1]

Where

${\tau }_e+{\rho }_e+{\alpha }_e=1$ [1]

For the calculation of the g-value are the direct transmittance \tau_e and the direct absorption \alpha_e needed. From the \alpha_e only the inward flowing fraction of the energy, the secondary absorptance q_i is relevant.

Direct transmittance \tau_e

Fehler beim Parsen (Unbekannte Funktion „\lamda“): {\displaystyle \tau_e = \frac{\sum S_y \tau(\lamda) \Delta\lamda}{\sum S_y \Delta\lamda}} [1]

Where S_y spectral distribution of solar radiation \tau(\lamda) spectral transmittance of the glazing \Delta\lamda range of wavelength

Inward flowing fraction of energy q_i:

single glazing fenestration

$q_i=frac{\alpha }_e{h}_i{h}_e+h_i$ [1]

Where h_e 23 \frac{W}{(m²K)} h_i 8 \frac{W}{(m²K)} – for borosilicate- und soda-lime-glass \alpha_esolar absorptance

(h_e and h_i are mean values with arranged conditions)

g-values are dimensionless and between 0 and 1

[1] DIN EN 410:1998 Glas im Bauwesen, Bestimmung der lichttechnischen und strahlungsphysikalischen Kenngrößen von Verglasungen