A study by the Passive House Institute: information for window manufacturers
In a modern, conventional, triple-glazed low-energy house, depending on the climate zone, heating costs of between 23 and 25 Euro per linear metre at the edge of the glass can be saved over the period of use if highly efficient plastic spacer bars are used in insulating glass windows instead of aluminium spacers.
Lower heating costs for customers – market opportunity for the windows industry
According to the study, end customers can save so much on heating costs that a window with a warm edge is worthwhile for them despite the slightly higher purchase price. For example: in the low-energy building with triple glazing looked at in the study, over a period of use of 40 years, that represents a saving of between 2463 Euro in heating costs in a cool/moderate climate, and 2260 Euro in the cold climate zone. In the low-energy building with triple glazing, the savings are 1864 and 1690 Euro respectively. For window manufacturers and insulating glass manufacturers, this offers a concrete economic opportunity, as high-quality plastic spacer bars are only slightly more expensive per linear metre to purchase than spacer bars made of aluminium.
Less building heating energy thanks to the warm edge
In comparison with aluminium spacer bars, the energy savings when using efficient plastic spacer bars were as follows:
in a cool/moderate climate
• in the low-energy building with triple glazing studied: 8.6 percent
• in the low-energy building with double glazing studied: 5.6 percent
• in the Passive House building studied: 22 percent
in a cold climate
• in the low-energy building with triple glazing studied: 7.1 percent
• in the low-energy building with double glazing studied: 4.8 percent
• in the Passive House building studied: 28 percent
These numbers confirm that the "warm edge” increases the energy efficiency of windows and thus of buildings.
It makes the difference: the heat transmission coefficient
After the glass and the frame, the spacer bar is the third most important component for the energy performance in modern heat insulating windows. If the spacer bar has a poor – i.e. high – heat transmission coefficient, a lot of heat is lost to the outside here – even with an excellent frame and high-tech glass. However, there are big differences in performance when using plastic spacer bars. A highly efficient warm edge, as used in the study, has a linear thermal conductivity of 0.14 W/(mK). The value for stainless steel is 0.6 and for the aluminium spacer bar – the clear back marker – it is a massive 160 W/(mK).
The study can assist you when providing advice and when making sales
For the first time, the study by the Passive House Institute has produced figures that demonstrate the benefits of warm edge spacer bars in comparison to other spacer bars in black and white. Window manufacturers can use these figures when advising customers and making sales.