Life Cycle Assessment (LCA) of window framings has a long tradition at the EMPA. The first studies were made as early as 1991. Results and methodology had a broad reach and enjoy internationally a good reputation. A part of the study commissioned by the Swiss Association of the window and cladding producer in 1996 (Richter, K. et al. (1996)), EMPA's LCA unit conduce further studies for major Swiss window producer.

Generally the conducted LCA's cover all the relevant phases in the product life:

• Production
  Fabrication and transport of the raw materials and the assembly of the window framings in the factory including auxiliaries, energy supply and waste handling
   
• Use phase
  Installation, maintenance, heat losses through different framings and glazing and finally dismantling. In order to assess the heat losses through the framing - which dominate the overall environmental impact by one order of magnitude - the EMPA developed a dynamic model to simulate specific realistic conditions including passive solar winning.
   
• End-of-life phase
  After the end of the building's life time, the dismantled framings are either disposed or processed further. As long as the materials represent a value, they are recycled and replace virgin material, thus saving resources. In order to reflect the actual recycling of the framings, the newer studies are based on a Value Corrected Substitution (VCS) of the virgin raw material with recycled one. This method was developed at the EMPA by Frank Werner (Werner F. and Richter K. (2000)) to reflect the actual decision context and to give incentives for recycling and product design.

Considering the heat losses through the window area, the use phase dominates the environmental impacts within the whole life cycle of a window framing. The impacts from heat losses are assessed to exceed the impacts from the production of the framings by one order of magnitude. Therefore it is recommended for environmental improvement first to minimise heat losses by choice of products (i.e. minimise the thermal conductivity of both glazing and frame) or architectural means (passive solar heat). As a secondary measure the material choice plays a role, where wood is considered environmentally soundest, followed by PVC and the best recyclable metal profiles, whereas the degree of possible recycling is more important than the choice of the material itself.

The study Richter, K. et. al. (1996) can be ordered in the web-shop through the SZFF homepage:
Richter K., Künniger T. and Brunner K. (1996) Ökologische Bewertung von Fensterkonstruktionen verschiedener Rahmenmaterialien (ohne Verglasung). EMPA-SZFF-Forschungsbericht, Schweizerische Zentralstelle für Fenster- und Fassadenbau (SZFF), Dietikon.

Contact: Mischa Classen

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