Energy transmittance

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The energy transmittance (also g-value , English Solar Heat Gain Coefficient , SHGC) is a measure of the transmittance of transparent components for energy. This indicates what percentage of the energy is generated by z. B. Sun exposure can get inside and there contributes to warming. The g-value as total energy transmittance is the sum of the direct transmission of solar radiation as well as the secondary heat dissipation inwards through radiation and convection . Loss occurs through reflection or absorption from or on the transparent component. The g-value takes values ​​between 0 and 1. A g-value of 0.7 indicates that 70% of the incoming energy is let through.

General

Transparent components are generally windows or glass components. The energy transmittance or g-value depends on the one hand on the transmittance for visible light , but above all for infrared radiation, which is also referred to as thermal radiation . Since this concerns the energy from the entire spectrum , no direct statement can be made from the g-value about the brightness in a room. The reflected portion of the energy is considered a loss, as it no longer contributes to the heating of the building. The absorbed portion, on the other hand, generates heat in the material and therefore contributes to the energy balance. However, this also causes energy to be lost to the outside world. In the case of double glazing, this loss through absorption varies greatly between the inner and outer pane, with a higher loss occurring on the outer pane.

Germany

Guideline values ​​for construction

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  • Usual single glazing: g = 0.75 - 0.87
  • 3-pane composite windows or 2-pane insulating glazing without coating (no longer common): g = 0.65
  • 2-pane insulating glazing with coating: g = 0.60
  • 3-pane composite window or 3-pane insulating glazing without coating (not common): g = 0.60
  • Glass blocks or wired glass: g = 0.60
  • 3-pane insulating glazing with coating: g = 0.5–0.55
  • special sun protection glass : g = 0.3–0.5. These glasses are often used in all-glass facades in order to minimize the heat input without sun protection.
  • KSD glass : The g-value is changed by turning the pane; in summer, for example, the g-value is 0.39 and in winter 0.65.
  • Switchable glasses : Here the g-value is changed by changing the light transmission of the glass pane. In the case of electrochromic glasses , for example, the g-value can vary continuously between 0.45 and 0.1, in the case of thermochromic glasses between 0.55 and 0.27.

Shading coefficient b

The shading coefficient b according to VDI 2078 is sometimes mentioned by the manufacturers instead of the g-value.
The numerical value is proportionally higher, since the g-value of the respective pane of glass is set in relation to the assumed g-value of double-pane normal glazing:
b = g / 0.8.

Until October 1994, reference was made instead to 3 mm single glazing with a g value of 87%: b = g / 0.87.

See also

Individual evidence

  1. ↑ Baunetzwissen , accessed in January 2016
  2. ↑ KSD solar diode window . Presentation folder of the website of Willi Maier GmbH, Glaserei und Fensterbau. Retrieved August 3, 2019.
  3. ↑ see p. 121 in Glasbau Atlas, Christian Schittich, Gerald Staib, Dieter Balkow, Matthias Schuler, Werner Sobek - Walter de Gruyter, 1 Jan 2006