window size
The size of the window mainly depends on the requirements of the room's lighting and ventilation, structural practices and architectural modeling, and must comply with the current "Building Modulus Coordination and Unified Standards". For windows used in general civil buildings, there are general atlases everywhere. The height and width of various windows are usually expanded with a modulus of 3M as the sign size of the opening. When necessary, just select the required type and size directly [5] .
Doors and windows "three natures"
The physical properties of doors and windows mainly include air infiltration, rainwater leakage, wind pressure resistance, thermal insulation, sound insulation, and lighting performance. Among them, the last three properties are selected and controlled according to the specific needs of room functions; the first three properties are the basic three properties of building doors and windows, that is, the so-called "three properties" of doors and windows. According to the provisions of "Classification and Testing Methods for Airtightness, Watertightness and Wind Pressure Resistance of Building Doors and Windows" (GBT7106-2008), building doors and windows have different classifications according to different performance indicators [5].
Air-tightness index of doors and windows: The classification of air-tightness of doors and windows is based on the air infiltration volume q1 per unit opening seam length and the air infiltration volume per unit area q2 when the pressure difference is 10Pa under standard conditions. Level 8 [5].
Watertightness index of doors and windows: The classification of watertightness of doors and windows is to use the pressure difference of the previous level of the severe leakage pressure difference as the classification index, and divide the doors and windows of the building into 6 grades [5].
Wind pressure resistance index of doors and windows: The classification of wind pressure resistance of doors and windows is based on the grading detection pressure difference P3 as a grading index, and the doors and windows outside the building are divided into 9 grades [5].
In addition, building doors and windows also have relevant standards and corresponding grading indicators in terms of air-borne sound insulation performance, thermal insulation performance and lighting performance. Therefore, in the selection of doors and windows, the types and grades of doors and windows should be reasonably determined and selected according to factors such as climate, building height, and room use requirements in various regions, and the requirements of relevant performance indicators should be met [5] .
Door and window energy saving
Building doors and windows are the weakest parts of the building envelope with the weakest thermal performance, and their energy consumption accounts for 40% to 50% of the total energy consumption of the building envelope. At the same time, doors and windows are also heat-receiving components in the building, which can obtain solar radiation through the transmission of sunlight into the room, so it is an important factor affecting the indoor thermal environment of the building and building energy saving [5].
In order to achieve a good energy-saving effect for doors and windows, in addition to satisfying the three basic performances, local climatic conditions, functional requirements, architectural forms and other factors should also be comprehensively considered, and the requirements of the national energy-saving design standards for door and window design indicators should be met.