Warm edge – Profile bars of the future

There are different approaches to thermally improved glass edge bond: hollow profile bars (“rods”) made from materials with low thermal conductivity, flexible foam spacers on coils or thermoplastic material from drums. You can find an overview of the presently offered “rods” in my latest article in issue 5/2015 of GLASWELT here, including a glimpse at the future of warm edge (Article is in German language).

BF Technical Webinars: Autumn/Winter Semester 2015

The new BF-Webinar program (in German language) is available now – restructured, cleared and more organized. The basic courses are offered autumn/winter 2015, the courses of spring/summer 2016 will be based on them. You can find a description of the full webinar program in the new BF-Webinar-Flyer here (sorry, only available in German language).

My contribution to the autumn/winter program this year are two webinars:
Wednesday, October 14th, 2015, 10:00 “Abstandhalter / Warme Kante – Teil 1” (spacers / warm edge part 1)
Monday, December 7th, 2015, 10:00 “Glasbruch – Teil 1” (glass breakage part 1)

Registration for interested parties is quick and easy through the BF websites here. The fee per webinar and participating company is 95 EUR.

Dates for the autumn/spring webinars in 2016 are not yet fixed, but I will offer the following topics:
Abstandhalter / Warme Kante – Teil 2 (spacers / warm edge part 2)
Glasbruch – Teil 2 (glass breakage part 2)
Sprossen (new) (muntin/georgian bars)
Kondensation bei Isolierglas (new) (Condensation on insulating glass)

As soon as the dates are available, I will announce them on this page.

Extended scope for application of BF data sheets ‘Psi values for windows’

The data sheets ‘Psi-values for windows” of the Working Group Warm Edge of the BF Bundesverband Flachglas (German Federal Flat Glass Association), containing representative Psi-values for windows for thermally improved spacers are suitable for a simplified verification of Uw-values of windows. However, it is not allowed to use them for each and every window, especially not for facades. The application is only possible according to the ift guideline WA-08.

For wooden-, wood-aluminium- or PVC-windows for example, the representative Psi-values can only be applied for frame-U-values Uf greater than or equal to 1,0 W/m²K, and for aluminium-windows as far as greater than or equal to Uf ≥ 1,3 W/m²K. A minimum depth of glass insertion into the frame profile of 13 mm is required as well as the fact, that the real frame profiles must be comparable with the representative frame sections shown on the data sheets. The data sheets must not be used for windows with unprotected glass edge.

Driven by steadily increasing demand on thermal insulation of building envelopes, window systems are thermally-wise continuously improved. After all, they play a key-role in energy-efficient building. This is only possible if the thermal transmission coefficients not only of the glazing, but of the frame profiles as well are optimized, i.e. reach lower values. The level of thermal insulation of the frame profiles should not differ too much from the excellent U-values of modern triple insulating glass, to avoid problems like condensation to move from the glass surface to frame or reveal. The number of systems with Uf-values below 1,0 W/m²K is growing.

To open the use of the data sheets for those highly insulating frame systems as well, the Working Group Warm Edge run another project. ift Rosenheim made an analysis, under which conditions the application of the existing data sheets could be allowed for better = lower frame-U-values as well. Result is an extension of the scope of application according to this chart:

The chart shows the relevant requirements on Uf-values for window frame profiles for the application of representative Psi-values. Highly insulating frames must have a depth of glass insertion of minimum 18 mm.

Source: BF Bulletin 004 – Guide to ‘Warm Edge’ for windows

The updated ift guideline WA-08/3 is available since February 2015. It can be ordered from the ift Rosenheim online-shop, as pdf-file for download or as a printed copy (here).

Moreover, the ift guideline specifies requirements on the thermal transmission coefficient of the glazing, Ug and on the pane thicknesses. For panes thicker than 4 mm, surcharges have to be applied on the representative Psi-values.

Explanations can be found in detail in the ift guideline, and also in the updated version of the BF Bulletin 004, Guide to ‘Warm Edge’ for windows, published by the Bundesverband Flachglas (download here)

Warm Edge – Where is the journey heading?

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).


Glasstec 2014 – News about “warm edge”?

In a contribution to the column “Pro & Contra” of the October issue of the German magazine GFF-Magazins [here], I anticipated no quantum leaps regarding warm edge technology, shown on Glasstec 2014 in Duesseldorf. During my visit of this spectacular event, I could verify my point of view – no revolutionary new material or machine technology were exhibited, but I found an increase in options for existing solutions, and that both regarding material and machines for processing. You can find details in my latest article in GFF-Magazin, issue 12/2014 [here], (I apologize that it is all in German language.)

Please note

The office of the Consultant for warm edge and glass has been moved from Herrenberg to Boeblingen, closer to the captital of the German federal state Baden-Wuerttemberg. Please note the new contact data at the bottom of these pages.

As soon as everything is unpacked, you will find here again regular contributions to the subject of thermally improved insulating glass spacers, glass and other related topics.

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

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 .

Safe and tight?

During all those discussions about the third position after the decimal point of Psi-values, sometimes I miss other important aspects of insulating glass, like for example the durability of the edge bond. World’s best warm edge system would be worth nothing, if it allows for the gas fill to leak from the gap between the panes, because this worsens the Ug-value. Or if the unit fails untimely, because humidity can get into the gap and condensate on the inner glass surfaces. In my latest article for the magazin GLASWELT, I explain what is important for the processing of warm edge spacer systems and for the quality of insulating glass units. You can read the article in German language here.

BF Webinars Glass breakage – remaining spots available

On Thursday, April 24th, 2014, the BF (German Glass Association “Bundesverband Flachglas” will again present my one-hour webinar “Glasbruch – Grundlagen” (Breakage of glass – basics, the webinar will be in German language). I will explain the basics of material science and the properties of glass. A short look into linear-elastic fracture mechanics will illustrate why and how glass breaks and how to predict that.

The second part “Glasbruch – Vertiefung” (Breakage of glass – advanced training, in German language) on Tuesday, May 13th, 2014 will broaden the matter and inform about the different ways to break of different glass types. I will talk about thermally and mechanically induced glass breakage as well as about their possible causes.

Are you interested?
Then click here and register on the BF website (in German language).

Well advised with warm edge: Legal situation

In the newsletter ‘e-transparent’ of December 2013, the German association Bundesverband Flachglas had published a legal experts comment to the question whether warm edge would be “state of the art” and what this would imply for the obligation to advise clients properly in Germany. In a contribution for the journal GLASWELT, I picked up the matter and explained the different technical standards. You can read, why you are well advised with warm edge in my article here (in German language).