Psi data sheet

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 ‘Guide to warm edge’ now available in English and French

September 19th, 2016. 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.

Psi values for facades

June 23rd, 2016. 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.

Only new BF data sheets valid

January 6th, 2014. This is just to remind on time, at the beginning of 2014, that old BF-data sheets “Psi-values for windows” with representative Psi-values simulated from individual material values have lost their validity. According to a decision of the BF Working Group “Warm Edge”, from now on only data sheets with Psi-values determined with the measured equivalent thermal conductivity of the spacer are valid.

My recommendation: Do not save data sheet copies locally on your computer. In case of need just download the data sheets always newly from the website of the BF Bundesverband Flachglas. This will ensure that you are always up-to-date.

You can find the link on my literature list, or directly here.

Psi data sheets for windows updated

May 18th, 2013. The revised data sheets with Psi values for windows have been published just now. You can download them for free on the BF website (German Glass Association Bundesverband Flachglas) here.

The updated data sheets can be recognised  by the release index “April 2013”. Different from the first data sheet versions, where the representative Psi-values for windows have been calculated from individual thermal conductivity values of all the materials composing a spacer, now the Psi-values are determined on the basis of a measured equivalent thermal conductivity value of the complete spacer system including desiccant and butyle. An ift-Rosenheim guideline gives a detailed description of the measurement method – here.

Manufacturers of warm edge systems are allowed to still use old data sheet versions for their products, but they will expire latest 31.12.2013. Coexistence of old and new data sheet version for one and the same spacer system is not allowed. A research project of the BF working group “warm edge” served as a basis for the revision of the data sheets. First information about this research project can be found here (in German language). More will follow in the relevant specialist publications.

As usual, I will keep you informed here in this place.

New ift-guideline Thermally improved spacers

March 18th, 2013. Further to my previous announcement, ift Rosenheim, Germany, has published another ift-guideline about warm edge: WA 17/1 “Thermally improved spacers – Part 2: Determination of the equivalent thermal conductivity by means of measurement”. This guideline is a result from the latest research project of the working group “Warm Edge” of the German association Bundesverband Flachglas (BF). The guideline explains how to determine the so-called equivalent thermal conductivity value λeq,2B of a spacer and how to use it for the simulation of Ψ-values of windows according to EN ISO 10077-2, instead of a detailed geometrical spacer model with a multitude of individual conductivity values of the spacer constituents.

In comparison, this is a simple and pragmatic solution for obtaining of spacer input data for individual simulations. It helps to avoid mistakes with the modelling of rather complex spacer geometries. Furthermore, from now on, the “representative Ψ-values”, published on the BF data sheets “Psi-values for windows” will be determined according to this guideline.

The ift-guideline can be ordered in German language here. An English version will follow soon.

News from the Working Group “Warm Edge”

February 20th, 2013. During yesterday’s meeting in Rosenheim, the Working Group “Warm Edge” of the BF Bundesverband Flachglas agreed to update the data sheets “Psi-values for windows”. As a result of the latest research project of the Working Group, the representative Psi-values stated on the data sheets shall be simulated on the basis of measured equivalent thermal conductivity values of the warm-edge systems, and not as before with individual values of the sometimes complex product components.

The measurement method is described in a new guideline of ift Rosenheim, which will be published soon. Within the next weeks, the new data sheets will be available for free download on the BF websites. Warm-Edge manufacturers may utilize the old data sheets for their products until December 31st, 2013, after that deadline they will expire. You can find a first info (in German) about the research project here. More will follow in the relevant technical press – I will let you know here in my blog and in my literature list.

The Working Group “Warm Edge” consists of well-known manufacturers of warm-edge-systems, representatives from glass industry and members from higher education and research.

Do you have wishes or suggestions for the Working Group? If so, let me know!