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[[Plus:Test]]
The g-value is a value for the pass of energy through a transparent component.
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.
It is composed of direct solar radiation and heat emission by secondary absorptance to the inner space.
Zeile 23: Zeile 22:
:<math>g = \tau_e + q_i [1]</math>
:<math>g = \tau_e + q_i [1]</math>


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


transmitted part \tau_e \phi_e direct transmittance \tau_e
The radiation power <math>\phi_e</math> through the component can be separated as following:
<br />reflected part \rho_e\phi_e direct reflectance \rho_e
 
<br />absorbed part \alpha_e \phi_e direct absorptance \alpha_e  [1]
transmitted part <math>\tau_e \phi_e</math>    direct transmittance <math>\tau_e</math>
 
reflected part <math>\rho_e\phi_e</math>        direct reflectance <math>\rho_e</math>
 
absorbed part <math>\alpha_e \phi_e</math>      direct absorptance <math>\alpha_e</math> [1]


Where
Where
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:<math>\tau_e + \rho_e + \alpha_e = 1</math> [1]
:<math>\tau_e + \rho_e + \alpha_e = 1</math> [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
For the calculation of the g-value are the direct transmittance <math>\tau_e</math> and the direct absorption <math>\alpha_e</math> needed. From the <math>\alpha_e</math> only the inward flowing fraction of the energy, the secondary absorptance <math>q_i</math> is relevant.
:<math>\tau_e = \frac{\sum S_y \tau(\lamda) \Delta\lamda}{\sum S_y \Delta\lamda}</math> [1]  
 
 
Direct transmittance <math>\tau_e</math>
:<math>\tau_e = \frac{\sum S_\lambda \tau(\lambda) \Delta\lambda}{\sum S_\lambda \Delta\lambda}</math> [1]  


Where
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:
<math>S_\lambda</math> spectral distribution of solar radiation
 
<math>\tau(\lambda)</math> spectral transmittance of the glazing
 
<math>\Delta\lambda</math> range of wavelength
 
 
Inward flowing fraction of energy <math>q_i</math>:


single glazing fenestration
single glazing fenestration


:<math>q_i = frac{\alpha_e h_i}{h_e + h_i}</math> [1]
:<math>q_i = \frac {\alpha_e h_i }{h_e + h_i}</math> [1]


Where
Where
h_e 23 \frac{W}{(m<sup>2</sup>K)}
h_i 8 \frac{W}{(m<sup>2</sup>K)} – for borosilicate- und soda-lime-glass
\alpha_esolar absorptance


(h_e and h_i are mean values with arranged conditions)
<math>h_e</math> 23 W/(m<sup>2</sup>K)
 
<math>h_i</math> 8 W/(m<sup>2</sup>K) – for borosilicate- und soda-lime-glass
 
<math>\alpha_e</math> solar absorptance
 
(<math>h_e</math> and <math>h_i</math> are mean values with arranged conditions)
 


g-values are dimensionless and between 0 and 1
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
[1] DIN EN 410:1998 Glas im Bauwesen, Bestimmung der lichttechnischen und strahlungsphysikalischen Kenngrößen von Verglasungen

Version vom 6. Juli 2009, 08:37 Uhr

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=τe+qi[1]


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

transmitted part τeϕe direct transmittance τe

reflected part ρeϕe direct reflectance ρe

absorbed part αeϕe direct absorptance αe [1]

Where

τe+ρe+αe=1 [1]


For the calculation of the g-value are the direct transmittance τe and the direct absorption αe needed. From the αe only the inward flowing fraction of the energy, the secondary absorptance qi is relevant.


Direct transmittance τe

τe=∑Sλτ(λ)Δλ∑SλΔλ [1]

Where

Sλ spectral distribution of solar radiation

τ(λ) spectral transmittance of the glazing

Δλ range of wavelength


Inward flowing fraction of energy qi:

single glazing fenestration

qi=αehihe+hi [1]

Where

he 23 W/(m2K)

hi 8 W/(m2K) – for borosilicate- und soda-lime-glass

αe solar absorptance

(he and hi 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

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