With the rising demand for improved energy efficiency of glass façades, the focus is increasingly shifting towards the glazing edge of insulating glass with multiple panes and structural glazing applications in particular. While the U-values of the glass itself have little left to optimize in terms of efficiency, there is still significant potential in the sealants and spacer bars used. A joint study initiated by sealant expert Dow and leading warm edge spacer bar manufacturer SWISSPACER shows that an optimal combination of the sealant and spacer bar can improve the U-value of a façade by more than 15% without changing the façade design.
With increasing demands for high energy efficient glass facades, the focus is shifting toward the edge of the glass, in particular for insulating glass with multiple panes and structural glazing applications. While the U-values of the glass itself have little left to optimize in terms of efficiency, there is significant potential in the sealant and warm edge spacer bars used. A joint study initiated by sealant expert Dow and leading warm edge spacer bar manufacturer SWISSPACER has revealed that an optimal combination of the sealant and spacer can improve the U-value of a façade by more than 15%, without changing the design of the façade. The study was carried out by Bauwerk (Rosenheim).
The idea behind the jointly initiated study came about during the course of product development. At Dow, the focus was on the patented silicone technology showcased at glasstec in 2018, DOWSILTM 3364 Warm Edge IG Sealant.
The innovative secondary sealant for gas or air-filled insulating glass with multiple panes has up to 45% lower thermal conductivity (λD = 0.19 W/mK) than conventional insulating glass silicone. With organic sealants, such as polysulphide or polyurethane, that value increases to over 50%. At the same time, depending on the design of the façade and the façade system used, the new edge seal silicone allows for up to 25% lower Psi values in warm edge designs. DOWSIL™ 3364 also increases the surface temperature on the inside of the glass by up to 1°C, thus reducing the risk of condensation and the formation of mould. The silicone, which is approved according to the European Directive for Structural Glazing (ETAG 002), shines in particular when it comes to its high adhesive strength, its temperature resistance up to +150 °C and its UV stability.
Innovation leader SWISSPACER is renowned for its high-performance warm edge spacer bars. Together with its partners, the Swiss company regularly develops new technology solutions, which contribute significantly to achieving the best in energy efficient window and façade solutions.
DOWSIL™ 3364 and SWISSPACER Ultimate – for significantly improved energy efficiency
Within the framework of the present study, different façade designs were studied with a conventional Polyurethane (PU) sealant, a standard silicone sealant, as well as DOWSILTM 3364 – each combined with a stainless-steel spacer bar or SWISSPACER Ultimate. The results are clear: DOWSILTM 3364 used with SWISSPACER Ultimate in a piece of triple glazing (40 mm) as part of an aluminium façade design (100 mm profile depth, element size: 1x2 m) achieved a U-value of 0.846 W/m2K – this means a heat transmission coefficient that is over 13% lower in comparison with the use of a stainless-steel spacer, which achieved a U-value of 0.976 W/m2K. With a conventional PU sealant and the stainless steel spacer bar, the same façade design achieves a U-value of only 1.002 W/m2K. The overall energy performance of the high-end solution is approx. 15% better.
Particularly impressive too in terms of condensation is the comparison with conventional sealant and a stainless-steel spacer bar. The combination of DOWSIL™ 3364 and SWISSPACER Ultimate results in a temperature on the inside of the glass that is 2 degrees higher. In a normal climate (room temperature 20°C and relative humidity 50%), condensation only forms with an outside temperature of -49°C.
New potential in high-performance façade design
Dow and SWISSPACER were extremely satisfied with the results of the study. Karl-Theo Roes, Head of Market Development and Innovation at SWISSPACER, explains: “The study demonstrates with clear figures that the sealant and spacer bar, which are components that are often neglected when looking at energy aspects, have an enormous impact on the energy efficiency of a façade structure. At the same time, they can reduce the risk of condensation and thus increase comfort. This allows architects and façade builders even more room for manoeuvre, particularly when it comes to designing and executing high-performance façades.”
Markus Plettau, Marketing Manager High Performance Building, EMEA at Dow, adds: “With our 'warm-edge silicone' DOWSIL™ 3364 and SWISSPACER Ultimate in all-glass façades with a toggle system, U-value improvements of up to 0.14 W/m²K are possible without a design change. The reduction of the buildings CO2 emissions associated with improved energy efficiency can be considerable. A sustainable system all round."
New and attractive solutions are possible for aluminium fabricators and smaller façade construction companies: all-glass façades with U-profiles (‘toggle systems’) are particularly suitable for small and medium-sized façades, as they are simple and cost-effective. Combined with the performance of DOWSIL™ 3364 and SWISSPACER Ultimate, they also boast excellent energy efficiency.
Building owners, architects and designers will be pleased to know that costly design changes or façade insulation will in many cases not be required. Energy efficiency and condensation problems that occur within complex façade geometries, all-glass corners or filigree all-glass designs can be addressed in the long term with this powerful combination of SWISSPACER and Dow.