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The development of the insulating glass edge bond

How warm edge spacers were developed, and why they increase the energy efficiency of buildings so successfully

Sustainability, climate protection and the safeguarding of resources and a healthy environment for future generations are key issues for all manufacturing industries today. The construction sector was one of the first to acknowledge these concerns, and it is now setting exemplary standards in energy-efficient building methods. An important element in this is the optimised  insulation of windows, doors and façades. Highly insulating spacers such as Thermix® from the German plastics specialist Ensinger have contributed to the sustainable increase in energy efficiency and living comfort achieved by modern insulating glazing. However, the foundations for this achievement were laid more than 150 years ago.

Milestones in the development of the insulating glass edge bond

In 1865 Thomas D. Stetson, an American, files a patent for double glazing. Dehydrated air is used for the insulation between the glass panes, which are glued together. Stetson has also already come up with the idea of thermally separating spacers. But the materials and sealants he uses are too permeable. The insulating glass is not gas-tight in the long term. Some 65 years later, in 1930, the American engineer C. D. Have takes the idea further. He uses metal spacers which are hermetically soldered to the glass. This type of insulating glazing becomes increasingly popular in North America and Europe over the following years. In 1955 an insulating glass without an edge bond arrived on the market. Here the glass panes were fused together at the edges and offset. In 1959 the German glass finisher Alfred Arnold develops the organically glued edge bond with a metallic, hollow profile perforated towards the space between the panes and an elastic sealant. The method is developed further to become the edge bond glued in two stages which is customary today. In the 1980s the term “warm edge” is coined in the USA. It comprises all spacers which are thermally improved compared with aluminium.

Thermix: The pioneer of a new generation of spacers turns 25

The next major step forward in the history of the insulating glass edge bond comes in Germany in 1993, when Georg Greubel, operating under his company name Thermix in partnership with Ensinger, develops and launches the first thermally optimised and coextruded spacer made from highly insulating plastic with a thin diffusion barrier made from stainless steel. The advantage: Thermix® can be processed on existing facilities almost as easily as metal. Corner connectors and muntin bars are soon added to the portfolio.

Ensinger is exhibiting:

Glasstec
23. – 26. October 2018
Düsseldorf, Germany

Fenestration Bau China
31.10. – 03.11.2018
Beijing, China

VETECO
13. – 16. November 2018
Madrid, Spain

BAU
14. – 19. January 2018
Munich, Germany

Pictures 1 and 2: Thermix® spacers from Ensinger increase energy efficiency through better thermal separation in the edge zone of insulating glazing.

As early as 1994, series production of warm edge spacers is started by development partner Ensinger, which ultimately acquires full control of Thermix® in 1997. But Thermix® is somewhat ahead of its time. In the 1990s, the standardised energy assessment of windows and façades does not even take account of the thermal bridge in the transition zone from glass to frame. Consequently, it is difficult to convey to many customers the added value offered by a warm edge. However, the architects from the growing passive house movement quickly recognise the benefits of Thermix®: lower energy losses mean a lower heating and cooling requirement, lower energy costs and lower CO2 emissions. Living comfort is also increased. Since the glass edge remains warm even when outside temperatures are cooler, barely any moisture from the room air is deposited at the edge of the glazing. As a result, the risk of condensation and mould formation decreases.

“The spacers at the edge of the pane influence the insulating effect of windows and façades throughout their useful life, which spans several decades”, explains Ingrid Meyer-Quel, who until 2011 was the Product Manager and Head of Sales for Thermix® and today is a freelance consultant for Warm Edge and glass. “If the spacer is made from steel or aluminium, then the high thermal conduction capacity of the metal means that lots of energy is lost in the edge zone of the glazing. Highly insulating plastic profiles, usually equipped with a thin diffusion barrier made from stainless steel, minimise this thermal bridge effectively.”

Picture 3: Thermix: Development milestones

Energy-efficient construction in China

The Thermix® warm edge spacer from Ensinger has been commercially available for 25 years now and is contributing worldwide to the introduction of sustainable, resource-saving buildings. In China too, owing to the high standards for energy-efficient construction and the trend towards passive houses, more and more insulating glass windows are being fitted with warm edge spacers. That is because a spacer that insulates well, when used instead of aluminium, improves the U value of a window by 0.1 to 0.2 W/m2K – with a UW of 1.0 W/m2K this corresponds to a good ten percent. Whether a room is being heated or cooled, it is hard to find a component that pays off more quickly for the client when it comes to efficiency, living comfort and environmental protection.

Picture credits: Ensinger GmbH, Germany.

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