EUROPEAN REFERENCE GLAZING STANDARDS

The data for performance of windows is for heat losses, heat gains and for light transmission. There are three main things to consider, solar gain through the window, light levels inside the room and heat losses through the window in the heating season. The properties are the solar energy transmittance (the g value), the visible light transmittance (Tvis) and the heat loss co-efficient (U value).

In effect this is a measure of heat gain. Also called solar factor, g-value is the measure of the total energy passing through the glazing when exposed to solar radiation. It is the sum of two values: the solar transmittance, Ts, which is the heat absorbed by the glass and re-radiated as long-wave inwards and Qi the secondary internal heat transfer factor. Qi is where the glass absorbs some of the energy converts it to long wave heat some of which is radiated back out and some radiated into the room. The g value is also called the Solar Heat Gain Co-efficient (SHGC) and the Solar Factor. It can also be calculated for double and triple glazings as the examples in the reference glazings.

The g value is also called the Solar Heat Gain Co-efficient (SHGC) and the Solar Factor. It can also be calculated for double and triple glazings as the examples in the reference glazings.

When the g-value of the glazing is combined with the value of the shading, this is the Gtot value. A  simplified method of calculating that value is described in EN13363/1 (now EN ISO 52022/1) and is also the recommended procedure of EN 14501 (new EN ISO standard still to be allocated) for calculating the solar energy transmittance of complex glazing (glass and shading figures combined). For an accurate assessment for building modelling the more accurate calculations of the detailed method in EN13363/2 (now EN ISO 52022/3) should be used

The Shading Co-efficient (SC) is a figure that indicates the improvement compared to a single pane of clear glass. Figure 1 shown above shows that a single pane of clear glass has a transmittance value of 0.87. Thus SC = gtot divided by 0.87 example Gtot 0.40 / 0.87 = 0.46.  As single glass would no longer usually be considered this value is now rarely used.

The Shading Factor (FC) is the ratio of the total solar energy transmittance of the blind and shading combination divided by the g value of the glazing alone.

U-value is a measure of thermal conductance which is the ability of a material to transfer heat by conduction, convection and radiation. All components of a building have U-values for example masonry, insulation materials, plasterboard and windows. The lower the value, the slower the heat loss through the material. Therefore a material with a low U-value is a good insulator. The U-value of glazing is always improved by installing blinds or shutters. So it is the temperature difference between inside and outside if there is not any solar radiation in W/M2C (watts per metre squared Kelvin).

This measure refers to the fraction of visible light transmitted into a room. As with the g-value we have to consider the measure of the glass in combination with the shading device. The value is between 0 and 1, where 0 means no light is transmitted and 1 means all visible light is transmitted. A Tv value of 0.25 means 25% of light is transmitted.

A more detailed explanation of these properties can be found in link to ES-SO guide book Solar Shading for Low Energy Buildings. Download ES-SO pdf

1. BS EN 410 Glass in Building – Determination of luminous and solar characteristics of glazing, 2011.
2. EN 14501, Blinds and shutters – Thermal and visual comfort – Performance characteristics and classification, 2005.
3. EN 14500, Blinds and shutters – Thermal and visual comfort – Test and calculation methods, 2008
4. CIE 130-1998 – ‘Practical methods for the measurement of reflectance and transmittance’.
5. Publication CIE No. 15.2 – 'Colorimetry' (second edition), Vienna.
6. EN 13363-1 – Solar Energy and Light Transmittance through Glazing with Solar Protection Devices – Part 1, Simplified Calculation Method, 2007.
7. EN 13363-2 – Solar Energy and Light Transmittance through Glazing with Solar Protection Devices – Part 2, Detailed Calculation Method, 2005.
8. EN 673 Glass in Building – Determination of thermal transmittance (U value) – calculation method, 2011.
9. ISO 10077-1 – Thermal performance of Windows, Doors and Shading Devices – Calculation of thermal transmittance, International Standards Organisation, 2006.
10. ISO 15099 – Thermal performance of Windows, Doors and Shading Devices – Detailed Calculations, International Standards Organisation, 2003.
11. BS EN 13125 Shutters and blinds – Additional thermal resistance – Allocation of a class of air permeability to a product, 2001.
12. EN ISO 52022/1 – Energy performance of buildings -- Thermal, solar and daylight properties of building components and elements -- Part 1: Simplified calculation method of the solar and daylight characteristics for solar protection devices combined with glazing
13. EN ISO 52022/2 – Energy performance of buildings - Building and Building Elements - Thermal, solar and daylight properties of building components and elements - Part 2: Explanation and justification. 
14. EN ISO 52022/3 – Energy performance of buildings - Thermal, solar and daylight properties of building components and elements - Part 3: Detailed calculation method of the solar and daylight characteristics for solar protection devices combined with glazing (ISO/DIS 52022-3:2015).