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.
BF-Bulletin 004 ‘Guide to warm edge’ now available in English and French
September 19th, 2016. 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.
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 www.bauenplus.de (website only available in German language).
Psi values for facades
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.
Background:
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
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).
Lukewarm edge? Does not exist!
February 5th, 2016. 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.
What helps against the heat of the summer?
August 7th, 2015. 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.
Warm edge – Profile bars of the future
May 28th, 2015. 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
May 3rd, 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’
April 3rd, 2015. 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)
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