What is the key point of energy saving for doors and windows?
1. Heat transfer coefficient of doors and windows
The heat transfer coefficient (K value) of doors and windows refers to the amount of heat transferred through a unit area in a unit of time. The larger the heat transfer coefficient, the more heat will pass through the doors and windows in summer and winter. The heat transfer coefficient of doors and windows is related to the materials of doors and windows (profiles, glass, rubber strips, etc.).
2. Air tightness of doors and windows
The air tightness of doors and windows refers to the ability to prevent air from penetrating when the doors and windows are closed. The level of air tightness of doors and windows has a great impact on heat loss. Changes in outdoor wind force will hurt room temperature. The higher the air tightness level, the less heat loss and the smaller the impact on room temperature.
3. Window-to-wall ratio coefficient and orientation
The window-to-wall area ratio refers to the ratio of the total area of external windows (including transparent curtain walls) in a certain direction to the total area of the wall in the same direction (including the window area), referred to as the window-to-wall ratio. Usually, the heat transfer resistance of doors and windows is much smaller than that of walls. Therefore, the heat and cold consumption of buildings increases with the increase in the window-to-wall area ratio.
As a measure of building energy conservation, it is required to determine the appropriate window-to-wall ratio under the condition of meeting lighting and ventilation. Generally speaking, the solar radiation intensity and sunshine rate in different directions are different, and the solar radiation heat obtained by windows is also different. The main way to save energy for doors and windows is thermal insulation. The measures include: selecting energy-saving window types, improving the thermal insulation performance of doors and windows, improving the air tightness of doors and windows, and determining the appropriate window-to-wall ratio and orientation.
4. Select energy-saving window types
The window type is the first-factor affecting energy-saving performance. The energy-saving effect of sliding windows is poor, while the energy-saving effect of casement windows and fixed windows is superior. Because the sliding window slides back and forth along the lower rail of the window frame, there is a large space on the upper part and a gap between the pulleys on the lower part. The window sash forms an obvious convection exchange up and down, and the convection of hot and cold air forms a large heat loss. Therefore, no matter what insulation profile is used as the window frame, the energy-saving effect cannot be achieved. There is usually a rubber sealing strip between the sash and the window frame of the casement window. After the sash is closed, the sealing strip is pressed tightly, leaving almost no gap, making it difficult to form convection. Heat loss is mainly caused by heat conduction between the glass, sash, and window frame profiles, radiation heat dissipation, air leakage at the contact point between the sash and the window frame, and air leakage between the window frame and the wall, so heat loss is relatively reduced. For fixed windows, since the window frame is embedded in the wall and the glass is directly installed on the window frame, the glass and window frame are sealed with rubber strips or sealants. It is difficult for air to form convection through the sealant, and it is difficult to cause heat loss. In fixed windows, heat conduction between the glass and the window frame is the main source of heat loss.