Uw-value

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 Bulletin 004 – typo gremlins got into the works

March 28th, 2017. Unfortunately, the typo gremlins got into the last version of the BF Bulletin 004 “Guide to ‘Warm Edge’ for windows and facades”, and that of all things in the formulas for the calculation of Uw and Ucw. Immediately upon discovery the typos were corrected. As of now, the latest version (Modification index 4, March 2017) is available for free download on the BF websites. Or you can directly get to the pdf-files of the Bulletin in German language here, to the English version here, and to the French please click here.

And again: Muntin and Georgian bars

June 26th, 2016. 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

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 – 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 .