Against the background of ever higher demands on the energy efficiency of glass facades, the edge bond of the installed facade glass and, in particular, structural glazing applications are increasingly coming to the fore.
While the U-values of the insulating glass itself can hardly be optimized economically, there is still considerable potential for optimization with the sealants and spacers used. The study initiated by Dow and Swisspacer proves that an optimum combination of sealant and spacer can improve the Ucw value of facades by up to 15 % and more.
The idea for the study carried out by Ingenieurbüro Bauwerk (Rosenheim) arose during product development. Dow focused on the patented silicone technology Dowsil 3364 Warm Edge IG Sealant presented in 2018. The secondary sealant for gas- or air-filled multi-pane insulating glass has a thermal conductivity that is up to 45 % lower than that of conventional insulating glass silicones (λD = 0.19 W/mK). In the case of organic sealants such as polysulphide or polyurethane, this is even more than 50 %.
At the same time, the new edge compound silicone enables up to 25% lower Psi values in warm edge constructions, depending on the façade design and system.
A further advantage: Dowsil 3364 increases the surface temperatures of the glass on the inside by up to 1 °C and thus reduces the risk of condensation and mould formation. Last but not least, the silicone, which is approved according to the EU directive for structural glazing (ETAG 002), convinces with its high adhesive strength, temperature resistance up to + 150 °C and UV stability.
Manufacturer Swisspacer has the warm edge spacer with the best values on the market. Together with its partners, the Swiss company regularly develops new technical solutions. The aim is to tap the full potential of highly energy-efficient window and façade solutions.
Hard stratch tests
As part of the current study, various façade constructions were tested with a commercially available polyurethane (PU) sealant, with a standard silicone sealant and with Dowsil 3364, each combined with a stainless steel spacer or Swisspacer Ultimate.
The results are clear: For example, Dowsil 3364 in combination with Swisspacer Ultimate in a triple insulating glass (40 mm) of an aluminium façade construction (100 mm profile depth, element size: 1 × 2 m) achieves a Ucw value of 0.846 W/(m2K). This means a heat transfer coefficient that is more than 13 % lower than that of a stainless steel spacer, where the Ucw value is 0.976 W/(m2K).
Swisspacer
With a conventional PU sealant and the stainless steel spacer, the same façade construction even achieves a Ucw value of only 1.002 W/(m2K). The overall energy performance of the high-end solution from Dow and Swisspacer is therefore over 15% better.
Formation of condensation only from - 49 °C
Compared to conventional sealant and a stainless steel spacer, the combination of Dowsil 3364 and Swisspacer Ultimate results in a 2 °C higher temperature on the inside of the glass. In a standard climate (20 °C room temperature, 50 % relative humidity), condensation only precipitates in this structure at an outside temperature of - 49 °C. The temperature of the glass is then increased by 2 °C on the inside.
The results of the study can be found on the following websites.
www.dow.com/construction
www.swisspacer.com
Matthias Rehberger / GLASWELT
