Abstract
Substituting existing windows for highly insulated glazing systems in Norwegian residential buildings may have a strong impact during the winter season due to the reduction of daylight availability. This paper investigates the consequences on the energy demand for space heating and electricity use for lighting of substituting existing windows with new windows and adding insulation in three apartment buildings located in Trondheim, Norway. The buildings were respectively built before the 1900s, in the first decade of the 1900s, and in the 1960s. The initial U-value of the external facades ranges from 0.96 to 0.26 W/m2K, and is lowered to 0.15 W/m2K after the renovation process. The U-value of the existing windows ranges from 1.6 to 2.8 W/m2K. The new windows have a U-value of 1.1 and 0.6 W/m2K. Scenarios are modelled to simulate the use patterns of artificial lighting in the apartments, based on occupancy schedules and required illuminance thresholds