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.


Lukewarm edge? Does not exist!

Just to clarify again: “warm edge” refers to insulating glass edge bond with a thermally improved spacer. There is a clear definition of “thermally improved”. It can be found in the relevant international standard for the thermal transmission coefficient of windows, ISO 10077 part 1, as well as in the standard ISO 12631 for the thermal performance of curtain walling. Both standards contain each a chart with linear thermal transmission coefficients Ψ (Psi-values) for spacers made of aluminium and steel and a second chard with lower values for spacers with thermally improved performance. In cases of coubt, the definition helps to decide which chart is the right to use.

According to this definition, spacers made from steel are definitely NOT thermally improved. “Warm edge” does begin with stainless steel spacers. Stainless steel has a considerably lower thermal conductivity compared to aluminium or steel – it’s not for nothing, that the handles of steel cooking pots are often made from stainless steel.

Therefore, it is definitely not ok to praise steel spacers as somehow thermally improved. And by the way: Just the colour black alone does not provide sufficient evidence for a good thermal quality. Lukewarm edge – something like that just does not exist.


BF Technical Webinars Spring/Summer 2016

The webinars offered by the BF in spring/summer will take up and continue the themes that were offered during the last semester (All webinars will be held in German language).

My contribution this time will be the following four webinars:

Wednesday, 20.1.2016 – Abstandhalter / Warme Kante – Teil 2 (Spacers / Warm edge – part 2)
Thursday, 3.3.2016 – Glasbruch – Teil II (Glass breakage – part 2)
Wednesday, 13.4.2016 – Sprossen (Glazing bars)
Thursday, 2.6.2016 – Kondensation bei Isolierglas (Condensation on insulating glass)

The full program including possibility for registration can be found [here] on the BF websites.

The apprenticed profession “Glazier” in Germany

The industrial academy for glass-, window- and facade engineering follows new and innovative ways to show the attractiveness of the apprenticed profession glazier and to recruit young talents for craft activities:

I like that!

What helps against the heat of the summer?

It is common knowledge that a thermos bottle keeps cooled matter cold and heated things hot. Nowadays, refridgerators are extremely insulated and everyone knows that otherwise, they would be bad power guzzlers. Have you ever fancied the idea to keep your fridge door ajar? Certainly not.

An air-conditioned building is nothing else than a huge refridgerator. But what can be observed during these hot summer days? Air conditioning is set to arctic temperatures and doors/windows are left wide open. Cooling energy is wasted, and the costs for its generation often exceed the heating costs of winter times. You may wonder, what this has got to do with ‘warm edge’. Now, of course, the thermal insulation of the building envelope matters for this question.

Despite the incredible heat of the summer, it should be comfortably cool inside a building. It is necessary to prevent the heat from getting into the building. Once it is inside, it requires a lot of effort and costs to get it out again.

It is always the heat that moves – provided there is a temperature gradient, no matter in which direction. For a heated building, a) transmission heat losses, i.e. direct heat transfer through the building envelope (walls, roof, windows, etc.) and b) ventilation heat losses through joints, leaky or in extreme cases open windows and doors have to be considered. As a matter of principle, the same mechanisms are working for air-conditioned buildings, only in opposite direction. On top are the effects of solar radiation through the glazing.

Meanwhile, it is well known that in winter, it is much more comfortable to live in a building with excellent thermal insulation. But not everybody realizes that the heat does not care if it moves from roomside to outdoors or from outdoors to the roomside.

Compared to a poorly insulated one, in a highly-insulated building it takes much longer for the summer heat to transfer to the inside – provided doors and windows are kept close, to prevent the hot air from getting in. (Over the long term, of course, this requires a controlled ventilation with heat recovery). The lower temperatures of the night are used for cooling the building down, and as soon as the outer temperature comes close again to the roomside temperature in the morning, all windows are closed and if possible shaded. Then, even during these days of extreme summer heat, you can stay inside a highly insulated building at comfortable 24 °C (75 °F), and this for outer temperatures of 32 °C (90 °F) and more.

What do you actually need for a highly insulated building? Highly insulated walls, highly insulated and air-tight windows with triple glazing – of course with warm edge for the glazing edge bond – plus exterior shading, to keep the unwanted solar radiation outside. (Don’t forget an energy-efficient controlled ventilation system!). Without the thermally improved spacers, i.e. with conventional aluminum spacers in the edge bond, the windows would have loopholes all around their glass edges, quickly conducting the heat to the inside.

Therefore: Investing right means making investments in saved energy, with improved thermal insulation of buildings. This is easy on your budget and protects the climate.

Heat, that is not allowed to penetrate into a building, does not require a costly air condition to transport it out again. It’s so simple.