How can I match manufacturers' glazing data?
We recommend following the 5-step process written in the Constructions Database User Guide (section 13.1).
The properties of glazing panes and constructions are published by manufacturers. The salient properties for an individual pane are the solar direct transmittance, reflectance and absorptance. These values should sum to one.
When creating a glass pane type (material); the direct transmittance, reflectance and absorptance may be used directly with no modification. However, for a double-glazed unit you will find that the solar radiant properties are usually given for the full unit rather than the individual layers. The properties given are typically U-value, short-wave shading coefficient and total shading coefficient. Separate U-values may be specified for the mid-pane properties and the unit as a whole, including the frame.
The procedure for matching glazing properties for a complete glazing unit is as follows:
- For any known glazing panes (for instance 6mm clear float), assign properties from the materials database.
- Make a guess for the properties of panes for which no specific data is available.
- Match the manufacturer’s mid-pane U-value by suitable choice of air gap resistance. The air gap resistance includes the effect of low emissivity coatings facing into the glazing cavity. Do not adjust the CIBSE Net U-value (including frame) or the emissivities of the outside or inside surface.
- Click on Derived Parameters to display the derived properties of the glazing and compare the shading coefficients displayed with those provided by the manufacturer. Adjust the reflectance, absorptance and transmittance of the unknown panes to match these parameters. Be careful to ensure that the sum of the reflectance, absorptance and transmittance is 1. If the manufacturer’s data is in the form of transmittances rather than shading coefficients, use the displayed values for T(D) and T(R) at 0º incidence. These transmittances are related to the shading coefficients by a factor of 0.87.
- Adjust the CIBSE Net U-value (including frame), by changing the frame %, to match the manufacturer’s value for this parameter. This operation must be done last, as the Net U-value is automatically updated to the calculated mid-pane U-value after edits to any other parameters.
For more details, please visit Section 13.1 of the Constructions Database User Guide: https://help.iesve.com/ve2021/hints___tips.htm
