UNDERSTANDING AND CALCULATING THE G-VALUE

What is G-Value?

G-value (sometimes also called a Solar Factor or Total Solar Energy Transmittance) is the coefficient commonly used in Europe to measure the solar energy transmittance of windows. Despite having minor differences in modeling standards compared to the SHGC, the two values are effectively the same.

SUNLIGHT AND SOLAR ENERGY

From a physical perspective, wave radiation penetrates into the inside of a building through the window — visibly in the form of light waves and invisibly as energy and heat. The radiation transmission is measured as the luminous transmittance τv and the total energy transmission g-value. In addition to the U-value (thermal transmission coefficient), the latter in particular influences the energy assessment of the window. If the U-value and g-value are in the correct proportion, the window can even pay into the energy account, and for passive houses, for example, is an important component in the energy and heating concept.

TOTAL ENERGY TRANSMISSION VALUE

The total energy transmission value (g-value) is used to assess the level of energy input. This is that part of the solar energy that enters a room through glazing in the wavelength range λ = 0,3 to 2,5 µm in total. The lower the g-value, the lower the amount of solar energy that is allowed to enter the room. The total energy transmission value is made up of the direct solar energy transmission τe and the secondary heat dissipation to the inside qi.

The g-value that is advantageous for a specific building depends on the type of building, the usage and the position and orientation of the building: For houses, a high g-value is favourable for saving heating energy in order to increase the energy gains in winter; however, the risk of overheating in summer must then be taken into account. Note also that the U-value of the glazing should be small to keep the transmission heat losses low.

LUMINOUS TRANSMITTANCE

The luminous transmittance τv specifies the proportion of visible irradiation (wavelength range λ = 0,38 to 0,78 µm) that passes through a transparent component perpendicularly. The larger the value, the more light that passes through the component. A higher luminous transmittance is favourable on the one hand to improve the level of daylight lighting in a room; and on the other hand, the outlook to the outside is brighter and the distortion of colours is lower.

STANDARD VALUES FOR THE TOTAL ENERGY TRANSMISSION VALUE

Glass type and designation

Structure

G

Ƭv

U

 

(mm)

[mm]

[-]

[W/m2 K)]

Single glazing

4

0,87

0,90

5,8

Double glazing

4/ZR/4

0,78

0,82

2,7

Triple glazing

4/ZR/4/ZR/4

0,67

0,72

1,9

Double heat protection glass, coated

4/ZR-AR/b4

0,63

0,80

1,1

Triple heat protection glass, coated

4/ZR-AR/4/ZR-AR/b4

0,50

0,71

0,5

SOLAR + triple protection glass coating

4/ZR-AR/4/ZR-AR/b4

0,62

0,73

0,6

Advice, care and expertise for professionals, whatever your requirements. Get in touch for more information.

  • Yorkshire
    Regent House
    John St
    Harrogate
    HG1 1JZ
  • 01423 203790
  • info@internormaws.com
  • Midlands
    Trident Park
    Poseidon Way
    Leamington Spa
    CV34 6SW
  • 01926 258001
  • info@internormaws.com
Privacy Settings
We use cookies to enhance your experience while using our website. If you are using our Services via a browser you can restrict, block or remove cookies through your web browser settings. We also use content and scripts from third parties that may use tracking technologies. You can selectively provide your consent below to allow such third party embeds. For complete information about the cookies we use, data we collect and how we process them, please check our Privacy Policy
Youtube
Consent to display content from Youtube
Vimeo
Consent to display content from Vimeo
Google Maps
Consent to display content from Google