Warm edge

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In the case of multi-pane insulating glass, a warm edge is an edge in which the spacer between the panes of glass is made of materials with low thermal conductivity . In the case of windows and doors, the term is also used across the board for improved thermal insulation in the area of ​​the glass inset on the sash element.

Until the 1990s, spacers made of aluminum were predominantly used in insulating glass . Since aluminum conducts heat well, the edge of the pane cooled down significantly at low outside temperatures. This cooling at the edge is only slight with newer spacers with low thermal conductivity, which is why one speaks of a warm edge .

The thermal insulation in the transition area from the glass to the frame is significantly influenced by the thermal conductivity of the insulating glass spacer, which connects the two or three individual panes at their outer edges to form the insulating glass unit. Together with a peripheral secondary seal, the spacer also seals the space between the panes from the outside.

Double-pane insulating glass is usually 24 mm thick (4 + 16 + 4 mm), three-pane glass 32 to 40 mm.

Improved thermal protection

The insulation performance of common heat protection glasses with two-pane construction has been increased to the physically possible limit through improved metal coatings and the filling of the space between the panes with the noble gases argon or krypton .

At the beginning of the 1990s, the heat transfer coefficient (Ug value) of double thermal insulation glazing was around 3.0 W / (m 2 K), today it is 1.1 W / (m 2 K). With triple thermal insulation glazing, Ug values ​​of up to 0.5 W / (m 2 K) can be achieved. The heat transfer coefficient indicates the amount of heat in Wh that passes through one square meter of a component per degree of temperature difference between the indoor and outdoor air in one hour. The smaller the value, the greater the thermal insulation.

In parallel to the optimization of the thermal insulation of the functional glass, the frame construction was improved. However, the better the glass and frame are insulated, the more clearly the aluminum spacer in the insulating glass edge seal becomes noticeable as a thermal weak point. The classic spacer acts as a thermal bridge on the edge of the glazing . If the temperature drops below the dew point , condensate forms , which damages the frame structure, especially in wooden windows and doors. The formation of condensation with double-pane insulating glass is largely avoided with a warm edge . In any case, it hardly ever occurs with 3-pane insulating glass.

In order to reduce the thermal bridge effect, spacers made of materials have been used since the mid-1990s, whose thermal conductivity is significantly lower than that of aluminum. Integrated glass elements such as rungs should also be made of materials with low thermal conductivity.

variants

There are now a number of different spacer systems for warm edges. In addition to profiles made of stainless steel , various plastic mixtures and structural silicone foam, injectable thermoplastic spacers made of polyisobutylene are used.

Composite systems made from biopolymers made from renewable raw materials are also available. Flexible foam profiles are applied from the roll, thermoplastic spacers from the barrel directly onto the pane. This requires special machine technology that enables a high degree of automation.

TGI

The plastic spacers made of polypropylene , named after the manufacturer as "TGI-Spacer", have a coating made of stainless steel foil on their back. Polypropylene has a low thermal conductivity and is used as the base material for the basic shape of the spacer, while the stainless steel casing ensures that the edge seal is tight and that the usual insulating glass sealants adhere well. The PSI values ​​of the 7 mm high spacer profile are between 0.038 and 0.049. It is available in black and gray in a width of 8 to 24 mm with 2 mm gradations.

Swisspacer

The "Swisspacer Advance" is made of plastic with an aluminum foil as a barrier layer . The PSI values ​​of the 6.5 mm high spacer profile are between 0.037 and 0.047. It is available in 17 colors. The frame corners are connected to one another with a special welding technique.

The "Swisspacer Ultimate" is made of plastic with a metal-coated plastic film as a barrier layer. The PSI values ​​of the 6.5 mm high spacer profile are between 0.030 and 0.036.

Bait space

"Ködispace" replaces a fixed spacer by applying it in liquid form directly to the glass. It is stated that the "matte black of the sealant" reflects the "frame color" so that the use of different colors is unnecessary. The PSI values ​​of the polyisobutylene sealant applied at a height of around 6 mm are 0.034 to 0.043. With the system, glass gaps are possible with a width of 4 to 18 mm in increments of 1 mm.

Calculation of the heat transfer coefficient

The heat transfer coefficient (U value) is calculated using the calculation method in accordance with DIN EN ISO 10077-1. In addition to the U-values ​​for the glass and frame construction and the respective surfaces of these two components, the linear heat transfer coefficient ψ (Psi) of the spacer is required for the calculation. This value (related to the respective edge length of the glazing) describes the additional heat flow caused by the interaction of the frame profile and the insulating glass edge , including the influence of the spacer. The higher the Psi value, the more energy is lost through the edge seal. The unit of measurement is W / (m K). 1 W / (m K) means that 1 watt of thermal energy is lost per meter of edge length and degree of temperature difference  .

By using warm edge spacers, the psi value can be reduced by up to 60 percent. How strongly the influence of the spacer affects the evaluation of the entire component depends very much on the format of the insulating glazing. For smaller panes, the effects are relatively larger glass units (for example, a square pane of 50 × 50 cm has an area of ​​0.25 m² and an outer edge of 2 m; a pane of 1 × 1 m has an area of ​​1 m² and an outer edge of 4 m length, i.e. four times the area, but only twice the outer edge length).

development

The introduction of thermally improved spacers accelerated with the Energy Saving Ordinance (EnEV) of 2002, which requires that the thermal properties of spacers be taken into account in calculations. On the basis of DIN EN ISO 10077-1, when determining the heat transfer coefficient for the entire window, not only the transmission heat losses through the glass and frame, but also the heat losses through the insulating glass edge seal are calculated.

This development is being further accelerated by the goals of the federal government to reduce CO 2 emissions. In the EnEV 2007 and EnEV 2009 , the requirements for the thermal insulation of buildings were tightened.

Individual evidence

  1. ↑ Material groups for warm edge spacers at www.warmekante.info
  2. ↑ Data sheet Psi values ​​for windows based on the measurement of the equivalent thermal conductivity of the spacers TGI-Spacer from Technoform Glass Insulation GmbH, April 2013 - No. 9 - Change index 3, working group 'Warm Edge'
  3. ↑ Data sheet Psi values ​​for windows based on the measurement of the equivalent thermal conductivity of the spacers Swisspacer Advance from Vetrotech Saint-Gobain (International) AG, April 2014 - No 24 - Change index 0, working group 'Warm Edge'
  4. ↑ Data sheet Psi values ​​for windows based on the measurement of the equivalent thermal conductivity of the Swisspacer Advance spacers from Vetrotech Saint-Gobain (International) AG, April 2013 - No 19 - Change index 0, 'Warm Edge' working group
  5. ↑ Data sheet Psi values ​​for windows based on the measurement of the equivalent thermal conductivity of the Ködispace spacers from Kömmerling Chemische Fabrik GmbH, July 2013 - No.11 - Change index 2, 'Warm Edge' working group

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