In recent years, placing so-called “warm edges” has become the standard for modern windows. This article will give you an introduction to what it is, what it is used for and the role of glass spacers in insulating aluminum windows.
Warm edge with insulating glass
Modern windows are made of multi pane insulating glass. During the construction process, the glass and window frame of the sealed connection will not come into contact.
The gap between the glazing and the frame is a major problem with thermal insulation. It is represented by a separate value that measures the insulating capacity of a window. This measurement is called the linear heat transfer coefficient and is denoted by the letter “g”.
This reading indicates heat conduction along the edge of the glass, which greatly affects the overall U-value of the window. Therefore, heat flow along the edge of the glass is critical to the overall thermal insulation value of the window.
Spacers are used to ensure that the edges of the glass do not touch the frame. These spacers used to be aluminum. Over time, it turned out that due to aluminum’s high thermal conductivity, the edges of the panes cooled significantly when the outside temperature was cooler.
In this case, aluminum acts as a thermal bridge. In extreme cases, cooling at the edge of the pane can even cause the temperature to drop below the dew point. A condensate then forms between the window and the frame. Moisture-damaged actually is set the scene at the very beginning.
To avoid this, new spacers for modern windows are made of materials with lower thermal conductivity. The following are mainly used today:
– Stainless steel
– Certain plastic mixtures
– Structural silicone as foam
– Polyisopropylene, usually covered with stainless steel
– Biopolymers (renewable raw material)
These new spacers create a warm edge, which means there is less chance of cooling at the edge of the pane, and the overall U-value of the window is improved.
These structures can reduce linear heat transfer coefficients by up to 60%.
The importance of the warm edge
Warm edges affect the overall performance of the window in different ways. In principle, one can assume that it affects small pieces of glass more than large ones. But this is only roughly true.
The length of the edge of the glass is particularly important for calculating the effect. Depending on the format of the pane, the size of the glass edge may vary. Its length is not proportional to the window area.
Even with triple glazing, edge insulation cannot be ignored. Because three discs are used here, the surface area of the edge is one-third larger overall. Therefore, the thermal protection of the edges plays a larger role (by about a third more) than a double pane of the same size.
In individual cases, the exact influence must also be calculated separately based on the thermal conductivity of the material used. The calculation method used for this is standardized in ANSI and is quite complex.