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[[http://resourcecenter.pnl.gov/cocoon/morf/ResourceCenter/article//93]] | [[http://resourcecenter.pnl.gov/cocoon/morf/ResourceCenter/article//93]] | ||
''ASHRAE Handbook 2005 Fundamentals'' | ''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. | |||
:<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 | |||
<br />reflected part \rho_e\phi_e direct reflectance \rho_e | |||
<br />absorbed part \alpha_e \phi_e direct absorptance \alpha_e [1] | |||
Where | |||
:<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 | |||
:<math>\tau_e = \frac{\sum S_y \tau(\lamda) \Delta\lamda}{\sum S_y \Delta\lamda}</math> [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 | |||
:<math>q_i = frac{\alpha_e h_i}{h_e + h_i}</math> [1] | |||
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) | |||
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 | |||
Version vom 30. Juni 2009, 13:34 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.
- Fehler beim Parsen (SVG (MathML kann über ein Browser-Plugin aktiviert werden): Ungültige Antwort („Math extension cannot connect to Restbase.“) von Server „https://wikimedia.org/api/rest_v1/“:): {\displaystyle 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
- Fehler beim Parsen (SVG (MathML kann über ein Browser-Plugin aktiviert werden): Ungültige Antwort („Math extension cannot connect to Restbase.“) von Server „https://wikimedia.org/api/rest_v1/“:): {\displaystyle \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 (SVG (MathML kann über ein Browser-Plugin aktiviert werden): Ungültige Antwort („Math extension cannot connect to Restbase.“) von Server „https://wikimedia.org/api/rest_v1/“:): {\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
- Fehler beim Parsen (SVG (MathML kann über ein Browser-Plugin aktiviert werden): Ungültige Antwort („Math extension cannot connect to Restbase.“) von Server „https://wikimedia.org/api/rest_v1/“:): {\displaystyle 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
