BF Bulletin 004 Guide to Warm Edge – 5th Update available now!

Böblingen, 5.8.2022. It was about time: The BF Bulletin 004 “Guide to Warm Edge” has been updated once again. The fifth revision from May 2022 is available now.

In addition to thermal aspects of the thermally improved insulating glass edge bond, the Warm Edge working group has now also dealt with questions relating to the systems’ suitability for use. In several sub-projects, the properties of spacers that can influence the durability of insulating glass units were investigated. For this purpose, test methods were developed in basic projects, according to which all spacer systems that have a BF data sheet with representative Psi values ​​were then tested.

These criteria include, for example, the linear thermal expansion of rigid spacer hollow profiles, but also the question of whether volatile substances could be released at higher temperatures, which show up as a visible deposit on the glass surface in the space between the panes (fogging). The bonding strength of profiles that are made up of several components and the UV resistance of systems with plastic components are also among the issues. You can find out more about that in this post.

In the meantime, some of these tests have been introduced as further requirements for a BF data sheet to be issued. In addition, explanations of different spacer categories have been included in the Bulletin.

The BF Bulletin 004 Guide to Warm Edge is available in four language versions with explanations on the use of the BF data sheets, either for free download on the BF website, or directly here (Deutsch, Englisch, Französisch und Polnisch).

On 05. August 2022|By |Miscellaneous @en|Comments Off on BF Bulletin 004 Guide to Warm Edge – 5th Update available now!

What else matters with spacers

September 12th, 2021. The durability of the edge seal is decisive for the service life of an insulating glass unit. This is not only a question of how carefully the components of the edge bond (spacer, desiccant, primary and secondary sealant) are processed in the manufacture of the insulating glass. The quality and suitability of the materials used also play a critical role.

The requirements for spacers are diverse and demanding: The profiles must be UV and temperature resistant, withstand the mechanical loads of insulating glass such as climatic and wind loads, be compatible with the other materials of the edge seal and offer a suitable adhesion surface for primary and secondary sealants. Above all, however, together with the primary sealant (butyl) the spacer must form a continuous sealing level from glass to glass all around the unit, because the inert gas filling enclosed in the space between the panes should not be lost over time. In addition, no water vapor must penetrate through the edge seal, otherwise the unit would become “blind”.

Apart from a type test according to EN 1279 Part 2 (long-term test method for moisture penetration) and Part 3 (long-term test method for gas leakage rate), there are currently no normative specifications for proving the suitability of a spacer system. That is why the Warm Edge Working Group of the BF Bundesverband Flachglas has been dealing with the criteria for the usability of spacers for several years. Several sub-projects such as the verification of the linear thermal expansion for spacers of categories B and C, the fogging test at elevated temperatures for categories B to E as well as the bond strength of the profile construction for categories B and C have already been completed (an explanation of the spacer categories can be found in this post). For these sub-projects, suitable measurement methods were first developed. All systems for which BF data sheets with representative Psi values ​​are already available were then tested using the newly developed procedures. Further sub-projects are currently planned or in preparation.

Based on these sub-projects, when today a BF data sheet with representative Psi values ​​is requested for a newly developed spacer system, extensive technical documentation must be submitted, which is deposited with the BF Bundesverband Flachglas (German Federal Flat Glass Association). This is to ensure that only those systems receive a data sheet that can be proven to work in practice.

On this subject, in cooperation with the warm edge working group, ift Rosenheim has developed the ift guideline VE-17, in which the test methods for the usability of spacers are presented in detail. The ift guideline can be ordered from ift Rosenheim here.

On 12. September 2021|By |Miscellaneous @en|Comments Off on What else matters with spacers

Spacer Categories

September 12th, 2021. In the Working Group Warm Edge of the BF, for the collective project on the usability of warm edge systems, spacers were divided into five categories based on EN 1279-1, Section 3, Figure 2 (see also ift guideline VE-17/1) :

Category A = fully metallic hollow profiles (e.g. profiles made of aluminum, galvanized steel or stainless steel)
Category B = non-fully metallic hollow profiles, with a metallic adhesion surface* to the sealants (e.g. profiles made of plastic with stainless steel as a diffusion barrier)
Category C = non-fully metallic hollow profiles, with non-metallic adhesion surface* to the sealants (e.g. profiles made of glass fiber reinforced plastic with composite foils as a diffusion barrier)
Category D = Hot applied flexible spacers (thermoplastic material)
Category E = prefabricated flexible spacers (foamed spacers from the roll)

* According to Section 3.24 of EN 1279-1, the adhesion surface of a spacer is considered to be “metallic” if it is made of rolled or extruded aluminum, galvanised steel, stainless steel, without organic surface treatment. According to Note 1 to the term, organic surface treatments are painting, organic coating, organic film or organic overspray.

On 12. September 2021|By |Miscellaneous @en|Comments Off on Spacer Categories

Update on Warm Edge

February 9th, 2021. With the title “Das ist der Stand bei Warmer Kante”, another article by the warm edge consultant on the situation of warm edge was published in issue 2-2021 of the GFF magazine. You can read here (in German language) which systems are currently available on the market, how they are divided into different categories according to EN 1279-1 and what the rules of EN 1279-1 Annex D are all about when replacing components.

In the same issue, an interview with the warm edge consultant on frequently asked questions was published (in German language), which you can find here as well.

On 09. February 2021|By |Miscellaneous @en|Comments Off on Update on Warm Edge

BF Data sheets: Abridged version for those in a hurry

February 24th, 2019. Those who want to make sure that their use of the BF data sheets with representative Psi-values for windows resp. for facade profiles is correct according to the ift guidelines now can utilize an abridged version of the BF bulletin Guide to ‚Warm edge‘ for windows and facades. A flow chart allows to clarify quick and easy, if for an individual case, the representative Psi-values are applicable and how:

  • for windows:
    Brief instructions for data sheets Psi values for windows [continue]
  • for facades:
    Brief instructions for data sheets Psi values for facade profiles [continue]


On 24. February 2019|By |Uncategorized|0 Comments

Great jubilee: 20 years BF Working Group Warm Edge

On November 13, 2018, the “Working Committee Warm Edge” met for a meeting in Rosenheim, to celebrate a special occasion: In November 2018, the founding of the working group celebrated its 20th anniversary. Reason enough to look once upon the success story of this active BF working group (BF= Bundesverband Flachglas, German Federal Flat Glass Association).

Hour of birth of the WG Warm Edge was the BF Symposium on November 11, 1998 in Troisdorf on the subject “Thermally insulating edge bond systems”. There, the idea arose to jointly think about a fair, correct comparison of the spacer systems. For the younger among the readers it should be noted that at that time, windows in Germany were declared with kF values, without taking the thermal bridge at the edge of the glass into account. Warm edge provided no benefit for the kF value, the European standardization was not yet introduced.

Right at the first meeting of the WG on January 27, 1999, a project for the definition of uniform measurement and test criteria for Warm Edge was started, in which the six participating warm-edge systems were calculated under the same conditions at ift Rosenheim. Other projects followed, including the research project Psi-values windows with funding by the DIBt (German Centre of Competence for Construction) and the participation of five calculating and three measuring bodies, in which calculations were compared with measurements and extensive basics worked out.

Many projects of the WG Warm Edge subsequently found expression in the standardization. This includes the definition of “thermally improved”, which can be found today in EN ISO 10077-1 and in the standard for calculating the thermal transfer coefficient of facades, EN ISO 12631.

Best known and most popular are the datasheets produced by the Working Group Warm Edge, published by the BF, with representative Psi values for windows and for facade profiles – generally known as the “BF Datasheets”. (Here you can download the datasheets for windows and for facade profiles). They allow window and facade manufacturers to save the hassle of calculating Uw and Ucw values with a detailed FEM simulation and still be able to take full advantage of the value advantage of Warm Edge. The datasheets are in use in many countries worldwide. Together with the BF Bulletin 004 “Guide to ‘warm edge’ for windows and facades” they are now available on the BF homepage in four languages (download of the BF Bulletin here).

Jochen Grönegräs, Managing Director of the BF Bundesverband Flachglas and a regular participant in the WG Warm Edge, is proud of the success story of the working group: “The WG Warm Edge is not only a long standing, but also a very active working group at the BF. Although its members compete hard with each other out there in the marketplace, they manage to discuss factual issues through technical content. What the WG has achieved over the past 20 years is something to be proud of and benefits all market participants. Together with the glass manufacturers represented in the WG, we ensure that the focus on customer benefit is always maintained.”

Warm edge is indispensable to the market of today. Nevertheless, the WG does not see itself at the end of its activity. “We still have many ideas!” says Ingrid Meyer-Quel, spokeswoman for the working group: “At the moment we are working on a larger project with the topic, what else has to be performed by a spacer in insulating glass. After all, the best thermal improvement will not do any good if one-sided optimization leaves other important functions behind. “For the safety of processors and users of Warm Edge, quality criteria for usability should be defined and measurement methods developed. You can look forward to the next twenty years.

The Working Group Warm Edge

The Warm Edge Working Party is a subcommittee of the Technical Committee of Bundesverband Flachglas. The participants in the working group are members and sponsoring members of the BF. Scientific support for the working group is provided by Mr. Norbert Sack, ift Rosenheim.

This article was a press release of the BF in January 2019.

News from the “Warm Edge” Working Party: Update of data sheets

In January 2018, a revision of DIN EN ISO 10077-2 was published, that now provides for two different methods to calculate the thermal performance of profiles. What does that mean for the representative Psi-values stated on the BF data sheets? This question was discussed during a meeting middle of 2017, when the Warm Edge Working Party decided to clarify this question with another project order to ift Rosenheim.

DIN EN ISO 10077-2 specifies a method for the calculation of the thermal transmittance of window frame profiles Uf and of the linear thermal transmittance of their junction with the glazing Ψg. The Psi-values for façade profiles are calculated according to this standard as well. A two-dimensional cross section of the window- resp. façade profile is modeled in appropriate software and rasterized with a resolution sufficient for the numerical simulation. Air-filled cavities are consigned with prescribed key figures, so-called equivalent thermal conductivity values („single equivalent thermal conductivity“), considering all three mechanisms of thermal transmission – conduction, convection and radiation.

The revised version of the standard dated January 2018 now includes an alternative approach for the treatment of air cavities. This new method is considerably more complex. It still considers the influence of thermal conduction and convection with an equivalent thermal conductivity value, but the heat transport through radiation inside the cavities is calculated separately according to the radiosity method.

According to DIN EN ISO 10077-2:2018-01 the simulator now can choose which of the two valid methods he wants to use for air cavities.

To determine the values of the BF data sheets, firstly, several test specimens made of stacked spacer profiles are measured with the guarded hot plate method according to ift guideline WA-17/1. Then, the equivalent thermal conductivity value of the spacer system is calculated with statistical evaluation from the measured results. Finally, with this declared conductivity value, the representative Psi-values stated on the data sheets are calculated according to DIN EN ISO 10077-2 and the prescriptions of the ift-guidelines WA-08/3 and WA-22/2. Aim of the project was to clarify whether if the choice of the calculation method has any influence on this determination of representative Psi-values. Based on the results it was planned to specify one of the two methods as a uniform procedure in the regulations of the Warm Edge Working Party.

Within the framework of the project to compare the methods, the cross sections of the representative window- and façade profiles and glazing designs were calculated with three spacers of different thermal performance. As expected the method only has minimal influence on the Psi-values, which is within the calculation accuracy. In nearly all cases of Psi-values for windows, a difference could only be recognized in the fourth decimal place. For façade profiles, the differences were slightly higher, up to 0.002 W/(m∙K).

During the meeting of December 5th, 2017, the BF Warm Edge Working Party decided, that from January 1st, 2018, all newly established data sheets shall solely be calculated with the new radiosity method. This will continue to allow for a real comparability. Because of the very minor impact, data sheets for windows published before January 1st, 2018 will remain valid, whereas the data sheets for façade profiles were recalculated according to the new method and updated end of October 2018.

The Warm Edge Working Party

The Warm Edge Working Party is a subcommittee of the Technical Committee of Bundesverband Flachglas. The participants in the working group are members and sponsoring members of the BF. Scientific support for the working group is provided by Mr. Norbert Sack, ift Rosenheim.

This text was a press release of the BF Bundesverband Flachglas of November 2018.

Another inventory on warm edge

March 5th, 2018. Just in time for the trade fair “fensterbau frontale 2018” in Nuremberg, Germany, the most important event of the industry this March, you can find my latest article with an inventory on warm edge in the journal GFF-magazine in issue 3/2018  – or directly here (in German language).

As before, I explain the advantages of warm edge for insulating glass and discuss the question why there are still spacers made from aluminium.

BF Webinars Spring/Summer 2018

February 4th, 2018. After a longer break, the German Federal Flat Glass Association (Bundesverband Flachglas) offers again the webinar program of the technical training series (all webinars in German language). Basically, those webinars are open for everybody.  Especially for newcomers in the glass industry, they are an excellent opportunity to quickly get an overview of the required knowhow. Primarily, the webinars of the fall/winter season focus on topics for beginners, whereas the  spring/summer will provide webinars for deeper knowledge.

My contribution as a speaker for the spring/summer 2018 program will be:

  • 28.2.2018 at 10am Abstandhalter/Warme Kante II (insulating glass spacers/warm edge part 2)
  • 8.3.2018 at 10am  Glasbruch Teil II (glass breakage part 2)
  • 15.3.2018 at 2pm Sprossen (glazing bars)
  • 26.4.2018 at 10am Kondensation bei Isolierglas (condensation on insulating glass)

You can find more information on the topics of my webinars as well as the full program (in German language)  here.

The Online application on the BF websites is here.

On 04. February 2018|By |Dates|0 Comments

Update to the Warm Edge Update

April 25th, 2017. 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.