Study by the institute EMU Systems shows performance of premium Warm Edge spacer bars: U-value can be improved by up to 23 % on the North American market

Highly insulated buildings score well with excellent energy efficiency and a high degree of living comfort. But if there’s one weak point they have in particular, it’s usually the windows. A recent study by EMU Systems now reveals that the performance of windows can be significantly improved through the choice of glass spacer.

What role does the window play in modern construction?

For years, the International Energy Conservation Code (IECC) has been urging the planning and construction of buildings that are more airtight and thus more energy efficient. However, well insulated buildings make it harder for moisture to escape and it ends up accumulating in the rooms. One particular weak point in terms of both energy losses and the precipitation of condensation is the windows – especially the glass edge. A recent study by EMU Systems from Colorado now confirms the impact that an inconspicuous component – the glass spacer – can have on the performance of the windows and ultimately on the building as well.

Is there a way to improve the performance of the window with simple means?

The choice of spacer bar has a big impact on the energy-related and thermal quality of the window. With highly energy-efficient spacer bars made from plastic, windows achieve excellent results for very little additional cost and have clear advantages in the Energy Rating.

What did the study look at?

In its study for the US and Canadian market, EMU Systems combined 5 glass spacers with 9 window frame profiles. The study investigates the thermal resistance on the frame, the glass edge and the window as a whole, as well as the surface temperature on the glass edge, on the basis of locally applicable standards and methods of calculation. It also examines the dew point on the glass edge on the basis of various climate zones – condensate and mould can form here and impact on the health of the building’s occupants and the lifespan of the windows. For the Canadian market, the study shows how premium spacer bars support “Energy Star” certification. 



Overview of the compared window systems and details.


What are the findings at a glance?

When making a comparison between simple aluminium and highly efficient plastic spacer bars, the premium Warm Edge spacer bar Swisspacer Ultimate emerges the clear winner: When used with a triple glazing unit in a vinyl frame, it improves the frame’s U-value by an impressive 31 %. Even in a high-performance solution with insulated wooden frame and triple glazing, the Swisspacer Ultimate improves the frame’s performance by about 28 %:



An equally impressive improvement is evident in the U-value of the glass edge: If a highly efficient plastic spacer bar is used instead of an aluminium one, the improvement in a simple wooden frame with triple glazing is almost 40 %:



If you consider the overall performance of the window, then here as well the Swisspacer Ultimate clearly has the edge. It improves the U-value of a window with triple glazing in a simple vinyl frame by over 23 % compared to the aluminium spacer bar. The Swisspacer Ultimate also leaves the conventional, improved stainless steel spacer trailing miles behind. In an insulated vinyl frame with triple glazing, the improved stainless steel spacer achieves a U-value that is a good 9 % better than the aluminium spacer bar. However, the Swisspacer Ultimate used in the same combination increases performance by over 15 %:



And what about living comfort? What are the findings here?

Particularly in highly insulated buildings, the window – especially the glass edge – is often the coldest point. Condensation can form here, causing mould that is harmful to health and can additionally impair the quality and lifespan of the windows. Highly efficient Warm Edge spacer bars made from plastic minimise the cold bridges on the glass edge and thus reduce the danger of condensation and mould forming. That is an important advantage for window makers because it increases customer satisfaction and reduces the danger of product defects.

The EMU study investigates how the spacer bar influences the temperature on the glass edge for various climate zones in the United States and Canada. The fRsi factor is used to prove which spacer bars can avoid condensation on the glass edge at different indoor and outdoor temperatures. For example, at an outdoor temperature of -30 °F (-1.1 °C) and an indoor temperature of 70 °F (21.1 °C), the temperature on the glass edge – when using the premium Warm Edge spacer bar – is over 11.3 °F (6.3 °C) higher than when using an aluminium spacer bar and offers a high degree of protection against condensation.

At temperatures such as those in a typical Canadian winter, for example, the picture is just as clear: At an outdoor temperature of 0 °F (-17.8 °C) and an indoor temperature of 70 °F (21.1 °C), the temperature on the glass edge when using the Swisspacer Ultimate is the highest of all presented window solutions. It is almost consistently over 50 °F (10 °C) and thus above the dew point.



Temperature difference on the glass edge (°F), compared to the aluminium spacer (Te=30°).


What effect do Warm Edge spacer bars have on the the CANADA Energy Star Rating?

Premium Warm Edge spacer bars come into their own precisely when it all comes down to achieving high levels of performance. The Energy Star label stipulates precise targets for the certification. The study for the Canadian market additionally shows how Premium spacer bars offer advantages for obtaining certification: Windows must not exceed a U-value of 1.05 W/m2K or must achieve an Energy Rating value of at least 40. While quality windows consistently achieve the U-value, the Swisspacer Ultimate does well in the calculation of the Energy Rating. At an average solar factor of 0.40, the required value of 40 can be achieved or exceeded only with the Swisspacer Ultimate and highly efficient window frames.



With the broadly used SHGCg of 0.40, only with SWS Ultimate and with the best performing window system is it possible to achieve and exceed an ER of 40.


Who is responsible for the study?

The study was commissioned by Swisspacer. EMU Systems are experts in virtual prototyping for the construction industry, building science nerds, and Passive House enthusiasts with company origins in Australia, experience in Europe, and new roots in Colorado. EMU`s mission is to close the gap between mainstream construction practices and advanced, proven building science, and to empower our industry to build for the future and for resiliency through builder training and simple, standard, Passive systems.