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.

Thermal bridges with windows and facades

June 27th, 2016. 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).

Windows with Muntin/Georgian Bars – better than thought

March 31st, 2016. 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.


Warm Edge – Where is the journey heading?

December 27th, 2014. Without doubt, an excellent thermal insulation is one of the most efficient measures to reduce energy consumption of buildings. As a consequence, windows and facades, key components of building envelopes, have to provide even better (lower) U-values. My latest article published in issue 12/2014 of German glass magazine GLASWELT here discusses the consequences for the development of warm edge systems (article is in German language).


Warm edge – the difference in energy loss is not worth mentioning!??

July 11th, 2014. It is a persisting opinion amongst some window producers, that warm edge would only have marginal influence on the heat loss through a window. Quote from the interview with a window manufacturer, printed in the German glass magazine GLASWELT 5/2014, page 58: “Und so viel Energie geht doch nicht über diesen Kanten-Unterschied verloren.” – And it is not that much energy that is lost through that difference in edge bond.

Good gracious! Maybe this was valid in former times, when thermal transmission coefficients of windows were on rather humble level. For window U-values of more than 2 W/m²K, the improvement by use of warm edge systems was not that much. During the past years though, windows went through an enormous evolution in thermal performance. Nowadays, Uw-values of windows for new buildings in Germany are in the range of approx. 1.1 to 0.8 W/m²K, and this Uw-value is for the whole window, including frame and thermal bridge at the glass edge – not only a center-of-glass value. By rule of thumb, the use of warm edge instead of conventional aluminium or steel spacers improves the Uw-value of wooden- or PVC windows by approx. 0.1 W/m²K – or for metallic windows up to 0.2 W/m²K. Considering that approximately reveals that the effect of warm edge is easily in the range of 10 % – of the overall energy losses through a window, note well!

But for all that, in new windows aluminium spacers still do occur, even if it is triple glazing. What a pity, to pass up the chance for improving the Uw-value. Why? Is it just a lack of knowledge or making false economies? After years of educational work on this area I have no more understanding for that. Compared to other measures for thermal optimization of windows, warm edge is simple to implement and in addition extremely economical. Once the new windows are installed without warm edge, they will stay like that for the next decades. The potential for energy saving is lost for a long time.

1Potential for thermal optimization of windows

This graph shows the energy losses of a single-winged window and how they are shared between the three window components glass, frame and edge bond. Furthermore it illustrates the potential for optimization. Starting point is a window with the dimension 1.23 m x 1.48 m, a frame share in the total window area of 30 %, an Uf-value of 1.2 W/m²K and triple glazing with an Ug-value of 0.7 W/m²K and edge bond with aluminium spacers.

The comparison shows the possible extent of improvement of the Uw-value through

– warm edge instead of conventional aluminium spacers
– improvement of the Ug-value of the glass area
– improvement of the Uf-value of the frame area

If you want to know more about that, you can read my article (in German language) in the
GFF-magazine of march 2014 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.

Impressions from BAU 2013 Munich

January 18th, 2013. How nice to almost exclusively see triple glazings with warm edge spacers in the exhibits of the wooden and pvc window producers of Hall B4, C4 and B5. It has got around that warm edge is advantageous because it improves the Uw-values. The further distribution of warm edge is unstoppable, same as for triple glazing.

Metallic systems though seem not yet to have taken the message entirely. Hall A1 still contained quite a few exhibits with double glazings, often with aluminium spacers. What a pity, considering the high thermotechnical sensitivity of metallic window and facade systems to the improvement of the transition area between glass and frame. The use of warm edge makes technical sense and is a economic measure. As for the next BAU 2015, I am confident that regarding spacer and glass, also the exhibits in hall A1 will be up-to-date.