Thermal Bridging Effect of Window-Wall Junction in Apartment Buildings using Current Installation Method of Window to Wall

Purpose: The insulation performance of walls and windows has been gradually improved. In the German passive house certification, the thermal transmittance of an installed transparent building component and the general thermal transmittance of window products are considered as certified factors. However, the method of installing windows to walls has not changed, and the thermal bridge of the window–wall junction is rarely evaluated during the design and construction stages. Therefore, it is necessary to quantitatively evaluate the effects of thermal bridges on the junction to improve the method of installing windows to walls. Method: In this study, the thermal bridges of window–wall junctions were quantitatively evaluated in the term of linear and point thermal transmittances. In addition, the installed thermal transmittances of actual windows in a domestic apartment building were calculated and compared with the designed thermal transmittance of the window. Furthermore, the annual energy requirements of the apartment were evaluated by including the installed thermal bridges. Result: The insulation performance improved with the decrease in the linear thermal bridges because the thickness of the insulation materials could have been increased. However, the point thermal bridges barely changed because the thermal conductivity values of the fixing brackets were very high. The installed thermal transmittances of the four types of windows increased by 1.1–1.2 times of the designed value, and the corresponding heating energy requirement increased by 4.2% annually.