U_g-value

The U-value of a glazing, called U_g value, indicates the heat transfer through the undisturbed, central area of ​​the glazing and is based on DIN EN 673.

g-value

The total energy transmittance of a glazing, called g-value, indicates the proportion of the incident radiation, which is transmitted by the glazing and is based on DIN EN 410.

g_tot – value

The total energy transmittance of glazing with sunscreen, called g_tot-value , indicates the proportion of incident radiation transmitted by this combination and is based on DIN EN 13363-2.

DIN EN 410

DIN EN 410 – Glass in construction – Determination of photometric and radiation physical parameters of glazing: specifies the calculation method for determining the photometric and radiation physical parameters of glazing.

DIN EN 673

DIN EN 673 – Glass in construction – Determination of the heat transfer coefficient specifies the method of calculation for determining the U value of a glazing.

The heat transfer coefficient depends on:

• Structure
• Gas filling
• Coating
• Mounting position

This takes into account:

• Convection
• Thermal radiation
• Heat conduction

U-value

The U-value indicates the heat transfer through a homogeneous solid. It depends on the boundary conditions of the thickness and the conductivity of the material. With the layer thickness (d) and the conductivity (l) the heat transfer resistance R_i = d / l is calculated for each individual layer. The sum of the internal resistances (R_si), outside (R_se) gives the total thermal resistance (R_T).

The U-value is now calculated from the reciprocal of R_T = 1 / R_T and is expressed in watts per square meter and Kelvin (W/m²*K).

Radiation-physical characteristics

The most important parameters are:

• Transmission τ (tau)
• Absorption α (alpha)
• Reflection ρ (rho)

τ + α + ρ = 1 or 100%