At last: comparability for warm edges

If the surface temperature of a thermal glazing window pane inside a room drops below the temperature of dew point of the air around it, condensation water will be formed. Warm edge spacers significantly reduce this unwanted effect.

The Bundesverband Flachglas e.V. (German Federal Flat Glass Association - BF) now offers specific data sheets developed for simple performance comparisons of spacers used in thermal glazing for warm edges.

Since the mid-90s thermal glazing makers have increasingly come to employ so-called warm edge spacers, next to the classical aluminium spacers. These provide for better thermal separation at the sash sections for insulating glass panes. This makes for reduced thermal conductivity of the glazing edge seal, significantly improving the heat insulation values of windows, doors and facades in the critical transition sections from glass to sash profiles. The effect of the so-called warm edge is that condensation of water on the inside of the window panes occurs only with significantly higher room air damp values, compared to the traditional aluminium profiles. The warm edge therefore prevents possible window frame damage, improving the energy balance of houses and raising residential comfort.

Until now difficult to compare

Meanwhile quite a large number of different warm edge spacers are available on the market. Over and above those of stainless steel, there are others made of various combinations of plastics and structural silicone foams as well as injection-moulded thermoplastic spacers made of polyisobutylene and polypropylene with some very thin coating of stainless steel foil. So far, any direct comparison of the performance of individual systems involved considerable expense. Thermal glazing makers as well as window and façade manufacturers wishing to test the effects of warm edge spacers on their individual designs first had to work hard to find out about the parameters of individual systems. Later these had to be integrated into calculations for thermal glazing structures and sash types.

Standardised ways for measuring and calculations

Since April 2008 data sheets of the Bundesverband Flachglas’ “Warm Edge” working group have now provided a first chance for a direct comparison of system-related linear heat transition coefficients (psi values) of spacers, defined on the basis of the same calculation and measuring methods. Nine spacer manufacturers as well as the glass making industry had been involved in preparing these data sheets. Scientific support came from the Rosenheim Institute for Window Technology as well as from Rosenheim University. For window materials such as wood, wood/aluminium, PVC and aluminium, representative psi values of 15 different warm edge spacers were defined both for double and triple glazing.

Manufacturers of thermal glazing and of windows may now benefit from these data sheets when calculating heat transition coefficients for their products. As a result of these new data sheets, calculation procedures have become easier and more transparent. Relevant psi values are available for every single sash type used in making double and triple thermal glazing. Users may quickly find relevant values for their specific products.

Following Bundesverband Flachglas, these new data sheets will also be relevant to quality and testing regulations for the Multiple-Insulated-Glazing Quality Association. In future the award of RAL quality marks for multiple insulated glazing will be dependent on a prior definition of psi values in keeping with the criteria developed as part of the project.

To complement these new data sheets, the Warm Edge working group prepared a guideline for window manufacturers. On several pages, the leaflet offers a wealth of important information on the topic of warm edges and it shall also contribute to providing a basis for standardised market approaches.

For more information on these new data sheets and related printed information please consult Bundesverband Flachglas e. V. (www.bundesverband-flachglas.de) and Gütegemeinschaft Mehrscheiben-Isolierglas e.V. (www.gmiev.de). The new data sheets can soon be downloaded from the two websites.

glasstec 2008 will show the progress reached in developing warm edges for thermal glazing. All makers of such systems shall be represented at Düsseldorf to show their latest product developments.