Energy-efficient windows – for how long? Gas concentration in sealed glazing units

Although energy-efficient windows are being increasingly used in buildings, there is limited number of publications in the field of their durability. There is a lack of experience and reliable methods of determi-nation of the durability and expected lifetime of gas filled sealed glazing units, different coatings on the glass and new types of spacers and sealants. The objectives of this project are to investigate the durability and expected lifetime of energy-efficient win-dows – to find out how the windows age and whether the U-value changes over time. In addition, it will also investigate and analyse possible problems that might be connected with energy-efficient windows. The project will scientifically evaluate the performance, durability and expected lifetime of energy-efficient windows. The work will be carried out through interviews, inspections, measurements and calculations in buildings with energy-efficient windows. So far, inspections show that the gas concentration in sealed glazing units is a little bit too low in most of the inspected windows, measured values are between 75 and 90 %. Gas filling in sealed glazing units de-creases the U-value by about 0.1-0.2 W/mK, which means that, if the gas concentration falls by 10 %, the U-value increases by 0.01-0.02 W/mK. In new windows, the average gas concentration should be about 90 %. 1