Impact of Window Frames on Annual Energy Consumption of Residential Buildings and Its Contribution to CO₂ Emission Reductions at the City Scale

Windows are among building components that have the strongest effect on thermal load. They play a significant role in heat loss in buildings because they usually have a largely higher thermal conductance than other components of the building envelope. Although many studies have highlighted the relevance of heat transfer through frames and aimed to improve their thermal performance, poorly insulated aluminum frames (thermal conductivity of aluminum is 160 W/m·K, while that of polyvinyl chloride [PVC] is 0.17 W/m·K) are still in use in Japan. Therefore, the U-values of different window frames were calculated, and annual thermal loads were calculated according to the window configurations, including the frame, glazing, and cavity. We focused on standard residential buildings in Japan with a total floor area of 120.6 m² (two-story building), and the number of newly built houses and the application rate of window configurations in 2019 were surveyed to estimate the CO₂ emissions by regions. CO₂ emissions were reduced by approximately 3.98–6.58% with the application of PVC frames. Furthermore, CO₂ emissions were converted into the amount of CO₂ gas absorbed by cedar trees, which cover nearly 18% of the total land area of Japan. In conclusion, analogous to the amount of CO₂ gas absorbed by cedar trees, the absorption effect was equivalent to 327,743–564,416 cedar trees. Changing the window frame material can facilitate a significant energy-saving effect as a considerable amount of energy is saved, especially at a city scale.