Update to the Warm Edge Update

Unfortunately, I made a mistake in my latest article for GLASWELT issue 4/2017: One BF-data sheet, W28 for TPS IGK 611 of IGK Isolierglasklebstoffe GmbH, is missing in the chart on page 96. Please find a corrected version of the article (in German language) here.

Warm edge – Update

Not that long ago, during GLASSTEC 2016, several new spacer solutions for thermally improved glass edge bond were introduced. My latest article for the GLASWELT-magazine gives an updated overview of the systems and informs about the latest trends. You can find the article (in German language) here.

News from the “Warm Edge” Working Party

The BF data sheets – which list representative Psi-values for windows and for façade profiles – published by the Bundesverband Flachglas e.V. (“BF” = German Federal Flat Glass Association) are often used to determine UW– and UCW-values. This comparatively simple (but standard-conforming) method is well known in the market – far beyond the borders of Germany. A new project of the BF “Warm Edge” Working Party now aims to permanently ensure trustworthiness and reliability of the declared values. 

The representative Psi-values of the BF data sheets for windows and for façade profiles are calculated according to EN 10077-2 using the so-called equivalent thermal conductivity λeq,2B, (which is determined by measurement). The basis for this approach, as well as for the validity and application of these representative Psi-values are the three ift guidelines about thermally improved spacers, namely WA-08, WA-17 and WA-22. To declare the value of λeq,2B, three pairs of test specimen made from desiccant-filled and butyl-equipped spacers are measured, followed by a statistical evaluation. The value is shown on the BF data sheets on the bottom under ‘Two Box model Characteristic values’ in ‘Box 2’.

Picture: In the future, the value λeq,2B, declared on the BF data sheets shall be rechecked on a regular basis. The value is not suitable for a comparison of individual thermal performances of warm edge systems. For that purpose, only the indicative Psi-values shall be used, because they also include the influence of the spacer height h2.

Apart from a few exceptions, the sole difference in calculating warm edge systems are the input data λeq,2B and the height h2 of the spacer box 2. Therefore, the value λeq,2B is particularly important. It determines the Psi-values which are the most important performance factors of spacer manufacturers in their daily competition.

Consequently, during their last meeting on February 9th, 2017, the members of the BF “Warm Edge” Working Party have agreed a voluntary commitment to scrutinize the equivalent thermal conductivity values λeq,2B every two years. This shall allow the detection of any deviations compared with the original measurements, and as an additional benefit will provide the security that the values declared on the BF data sheets are still correct. The costs of the procedure will be borne by the respective spacer manufacturers.

The measurements shall exclusively be made by ift Rosenheim. It is worth emphasizing that the samples for these check measurements shall be collected from the spacer processing companies in the market, and not supplied by the spacer manufacturers themselves.

From 1st of January 2017, the RAL Gütegemeinschaft Mehrscheiben-Isolierglas e. V. (“GMI” = German Multi-Pane Insulating Glass Quality Association) has already implemented an external monitoring of the insulating glass components spacer, sealants and desiccant. It aspires to later include the control of λeq,2B, planned to be done every two years, into the ‘RAL-GMI Quality monitoring and testing standards for multi-pane insulating glass’.

As of the first re-measurement, the currently valid BF data sheets, available online on the BF websites, will be equipped with an expiration date of validity. The first check and new dating of the data sheets shall take place in 2018.

The „Warm Edge“ Working Group

The ‘Warm Edge’ working group is a subcommittee of the Technical Committee of Bundesverband Flachglas. The participants in the working group are members and sponsoring members of BF. Scientific support for the working group is provided by Prof. Dr. Franz Feldmeier, Rosenheim University of Applied Sciences and by Mr. Norbert Sack, ift Rosenheim.

This is a press release of BF Bundesverband Flachglas and ift Rosenheim of March 2017



BF Bulletin 004 – typo gremlins got into the works

Unfortunately, the typo gremlins got into the last version of the BF Bulletin 004 “Guide to ‘Warm Edge’ for windows and facades”, and that of all things in the formulas for the calculation of Uw and Ucw. Immediately upon discovery the typos were corrected. As of now, the latest version (Modification index 4, March 2017) is available for free download on the BF websites. Or you can directly get to the pdf-files of the Bulletin in German language here, to the English version here, and to the French please click here.

BF-Bulletin 004 ‘Guide to warm edge’ now available in English and French

The BF-Bulletin 004 ‘Guide to warm edge for windows and facades’ is a good introduction to the topic of warm edge. It is a manual for the often used BF-data sheets with representative Psi-values for windows and for facade profiles and explains the boundary conditions for the use of the BF-data sheets according to ift-guideline WA-08 (windows) and WA-22 (facades).

By the request of many, the bulletin was translated into English and French language.

You can find both versions on the literature page of my website, or you can directly download the English paper here and the French one here.

BF Technical Webinars Autumn/Winter 2016

With some delay, I would like to draw attention to the next events of the training series BF Technology Webinars, offered by the BF Bundesverband Flachglas (German Federal Flat Glass Association). Basically, those webinars are open for everybody (but they are all in German language). Primarily, the webinars of this season focus on topics for beginners, whereas the next term in spring will provide webinars for deeper knowledge.

My contribution this time will be the webinar ‘Glasbruch – Teil I’ (Glass breakage – part 1), on November 29th, 2016. The date for my webinar about warm edge part 1 is already over, but in springtime 2017, more webinars will follow.

You can find the full webinar program of the present term including a description of their contents and the speakers and the online-application on the BF-websites here.

Thermal bridges with windows and facades

Just want to mention my latest article, published in issue 3-2016 of the German building magazine “bauen+” of Fraunhofer IRB-Verlag/Bundesanzeiger Verlag. Article is in German language, with detailed information about warm edge. You can find it here.

For details about the magazine “bauen+” please look at (website only available in German language).

Psi values for facades

The new BF data sheets ‘Psi values for facade profiles’ were just released on the BF websites. You can reach the page directly here.

Thermal transmission coefficients Ucw of curtain wallings are determined according to EN ISO 12631. For fixed glazings installed in a facade with mullion- and transom profiles, tables B.1 and B.2 in Annex B of this standard contain Psi-values Ψmg resp. Ψtg for the calculation according to the “component assessment method”. Alternatively, Ψmg resp. Ψtg of an individual case can be determined with FEM-software. It is in the nature of things that the Psi-values of fixed glazings in facades are much higher compared to the thermal bridge along the glass edge in a window sash. This is why it is not allowed to use the BF data sheets ‘Psi values for windows’ for facade glazings.

The Warm Edge Working Group of the German Federal Flat Glass Association ‘Bundesverband Flachglas’ decided to offer a solution for facades as well, that allows to make better use of the potential improvement of warm edge spacers compared to table B.2 of the standard, but without the need of a detailed simulation. In the 6th research project of the Working Group, ift Rosenheim firstly identified the fundamentals of the determination of representative Psi-values of fixed glazings in facade profiles and defined three representative facade profiles. Then the representative Psi-values for facades were simulated for the BF data sheets of the individual warm edge systems.

ift-guideline WA-22/1:
The new ift-guideline WA-22/1 “Thermally improved spacers – Part 3: Determining the representative Psi-values of facade profiles” gives a detailed description of the procedure and sets forth clear stipulations for the use of the representative values for calculation of Ucw. You can purchase the ift-guideline here, a table of content is available here.

“Instruction manual” for the BF-data sheets:
The lastest version of the BF-Bulletin 004 ‘Guide to warm edge for windows and facades’ contains a general introduction to the subject of warm edge and explains the boundary conditions for the use of the BF-data sheets for windows and for facades. As an extra, a chapter on the thermo-technical handling of windows with glazing bars was added. I strongly recommend reading that Bulletin! You can download the German version for free here. An english translation will be available soon as well, I will keep you informed.

And again: Muntin and Georgian bars

For the German glass and windows magazine ‘GFF-Magazin’, I wrote a comprehensive overview about glazing bars, i.e. about the types of glazing bars in insulating glass units, the origins of those bars, and why representative Psi-values for windows with glazing bars are much more favorable compared to the high surplus values to Uw. You can find the article here (unfortunately, it is in German language).

Windows with Muntin/Georgian Bars – better than thought

Glazing bars (Muntin or Georgian Bars, “Sprossen”) are an indispensible instrument to design the appearance of buildings. But not only aluminum spacers in the edge bond of insulating glass elements are thermally-wise disadvantageous. Bars between the panes of a multiple glazing create thermal discontinuities, that have to be taken into consideration when determining the Uw-value of windows.

In my new webinar “Sprossen” for the BF (German Federal Flat Glass Association) on Wednesday, April 13th, 2016, I will explain why such glazing bars occur on windows at all, which types of bars are possible with multiple plane insulating glass and how Muntin/Georgian windows can be determined thermally-wise in a fairer manner compared to the high surcharges from the product standard for windows, EN 14351-1. (The webinar will be in German language).

Online-signup to the BF-Webinars is possible here.