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.
April 15th, 2017. Not that long ago, during GLASSTEC 2016, several new spacer solutions for thermally improved glass edge bond were introduced. My latest article for the GLASWELT-magazine gives an updated overview of the systems and informs about the latest trends. You can find the article (in German language) here.
The BF data sheets – which list representative Psi-values for windows and for façade profiles – published by the Bundesverband Flachglas e.V. (“BF” = German Federal Flat Glass Association) are often used to determine UW– and UCW-values. This comparatively simple (but standard-conforming) method is well known in the market – far beyond the borders of Germany. A new project of the BF “Warm Edge” Working Party now aims to permanently ensure trustworthiness and reliability of the declared values.
The representative Psi-values of the BF data sheets for windows and for façade profiles are calculated according to EN 10077-2 using the so-called equivalent thermal conductivity λeq,2B, (which is determined by measurement). The basis for this approach, as well as for the validity and application of these representative Psi-values are the three ift guidelines about thermally improved spacers, namely WA-08, WA-17 and WA-22. To declare the value of λeq,2B, three pairs of test specimen made from desiccant-filled and butyl-equipped spacers are measured, followed by a statistical evaluation. The value is shown on the BF data sheets on the bottom under ‘Two Box model Characteristic values’ in ‘Box 2’.
Picture: In the future, the value λeq,2B, declared on the BF data sheets shall be rechecked on a regular basis. The value is not suitable for a comparison of individual thermal performances of warm edge systems. For that purpose, only the indicative Psi-values shall be used, because they also include the influence of the spacer height h2.
Apart from a few exceptions, the sole difference in calculating warm edge systems are the input data λeq,2B and the height h2 of the spacer box 2. Therefore, the value λeq,2B is particularly important. It determines the Psi-values which are the most important performance factors of spacer manufacturers in their daily competition.
Consequently, during their last meeting on February 9th, 2017, the members of the BF “Warm Edge” Working Party have agreed a voluntary commitment to scrutinize the equivalent thermal conductivity values λeq,2B every two years. This shall allow the detection of any deviations compared with the original measurements, and as an additional benefit will provide the security that the values declared on the BF data sheets are still correct. The costs of the procedure will be borne by the respective spacer manufacturers.
The measurements shall exclusively be made by ift Rosenheim. It is worth emphasizing that the samples for these check measurements shall be collected from the spacer processing companies in the market, and not supplied by the spacer manufacturers themselves.
From 1st of January 2017, the RAL Gütegemeinschaft Mehrscheiben-Isolierglas e. V. (“GMI” = German Multi-Pane Insulating Glass Quality Association) has already implemented an external monitoring of the insulating glass components spacer, sealants and desiccant. It aspires to later include the control of λeq,2B, planned to be done every two years, into the ‘RAL-GMI Quality monitoring and testing standards for multi-pane insulating glass’.
As of the first re-measurement, the currently valid BF data sheets, available online on the BF websites, will be equipped with an expiration date of validity. The first check and new dating of the data sheets shall take place in 2018.
The „Warm Edge“ Working Group
The ‘Warm Edge’ working group is a subcommittee of the Technical Committee of Bundesverband Flachglas. The participants in the working group are members and sponsoring members of BF. Scientific support for the working group is provided by Prof. Dr. Franz Feldmeier, Rosenheim University of Applied Sciences and by Mr. Norbert Sack, ift Rosenheim.
This is a press release of BF Bundesverband Flachglas and ift Rosenheim of March 2017
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.
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).
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.
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.
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).
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).
December 9th, 2014. 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.)
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