Overall evaluation of windows - possible improvements within 5 years

Development of windows has been focused on reducing the U-value of frame and glazing. Only in few cases the net energy flow through the window during the heating season has been evaluated and in that case often only for south oriented windows. Initial calculations on a single family house shows a 30 percent reduction in heating demand related to the total window area if a double glazed low energy glazing with low iron glass is used compared to use of triple glazed super insulating glazing due to the larger solar energy transmittance of the low iron glazing. The main goal of this project is to stimulate the development of windows with an improved overall energy performance in preparation for the coming Danish Building Code 2005. The overall evaluation includes the interaction of U-value, g-value, window-wall joint and conditions for application, e.g. influence on indoor thermal environment and risk of condensation - inside as well as outside. Participation of glass-, glazing- and window professionals ensures that the results of the project are realistic and could form the basis for product developments concerning energy efficient windows.