Windows with 30% better energy balance

The final goal of the project was to improve the energy balance of a window with at least 30%. As reference is chosen a common low energy glazing mounted in a wooden frame construction. In order to characterize the energy balance of a window with a single value a method has been developed, which combines the results from several different building types and building orientations. The energy balance of the reference window has been calculated to -50 kWh/m2 window area. A 30% improvement of the energy balance then corresponds to an reduction in net energy loss of 17 kWh/M2 window area. The main emphasis has been put on improvement of the frame construction and the interaction between frame and glazing. Several theoretical analyses have been carried out and a prototype construction has been made, that meets the goal of a 30% improvement of the energy balance. The prototype has been tested in the guarded hotbox facility at the institute and a total U-value of about 1.2 W/(m2 K) have been measured, which is a eduction compared with the reference window of 0.2 W/(m2 K). The improvements have primarily been obtained by replacing parts of the frame construction with polystyrene foam insulation. A new window concept with increased glass distance and part of the frame integrated in the glazing has been described as a result of the analyses carried out in the project. The large glass distance helps to reduce the traditional thermal bridge effect of the spacer and the integrated frame leads to an increase in transmitted solar energy. Furthermore, a controlled air exchange in case of pressure differences between the enclosures in the glazing and the surroundings is included in the concept which strongly improves the life time of the windows. The thermal performance will be better than traditional windows with super insulating glazings