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.