In the context of residential buildings in Germany, a significant proportion of 209 million window glazing units are in need of energy-efficient modernisation. The replacement of single glass panes, laminated glass, box-type windows and windows with uncoated insulated glass units (IGU), has the potential to save around 10.8 million tonnes of carbon dioxide per year. This equates to approximately 353 million m2 of glass area. As a result, a significant amount of glass waste is generated. An effective waste management strategy is predicated on the ‘7 Rs’: rethink, reduce, reuse, repair, regift, recycle and rot. The replacement of existing windows with new insulated glass units (IGU) results in a significant amount of carbon dioxide emissions during the production process. Glass as a highly durable and infinitely recyclable material is mostly cascaded as cullet into the hollow glass industry as cullet to fulfil the German recycling quota for container glass.
However, for the flat glass industry, which has high demands on the optical quality of the glass pane, the utilisation of a considerable proportion of glass cullet during the float glass process is challenging. This has prompted consideration of the potential for reuse of used window glazing, rather than its destruction and melt. This paper presents the results of a research study on used double glazing, which concentrates on non-destructive test methods for measuring the real thickness, the thermal transmission coefficient (Ug-value) and the solar and luminous characteristics. The specimens are taken from the same building and have been exposed to the same environmental conditions for the past three decades without replacement. The objective of the case study is to contribute to the ongoing academic and industrial discourse about the circular economy and sustainability.
