[China Aluminum Network] to measure whether buildings are energy-efficient, mainly consider three elements, namely the loss of heat (exchange of heat), the convection of heat and the conduction and radiation of heat. Heat conduction is the transfer of heat by the molecular motion of the materials used in the doors and windows. It is transmitted from one surface of the material to the Other, resulting in the loss of heat. The radiation is transmitted directly in the form of rays, causing heat loss; convection is through the doors and windows. The gap causes a circulation of hot and cold air, and the heat exchanges through the convection of the gas, resulting in heat loss. The heat loss of doors and windows is mainly through the following ways: loss of heat conduction from the profile, loss of radiant heat through the glass, and loss of air convection heat through the gaps between doors and windows. Therefore, the following key technical measures can be taken to improve the energy saving effect of building doors and windows.
1. Select the appropriate ratio of orientation and window wall area to reduce solar radiation
According to the variation of the solar altitude and azimuth angle, the southward opening of the building can reduce solar heat gain in the summer and increase the solar heat gain in the winter, which is a favorable architectural orientation. For example: Where we are located (Suzhou) The prevailing wind in the summer is the southeast wind. The southeast to the building is conducive to natural ventilation, and the solar radiation is not very hot, so in Suzhou, the southeast direction is the recommended direction.
In order to avoid excessively large window openings affecting building energy consumption, in the relevant standards for building energy conservation, requirements have been made for the windows of buildings, ie the area ratio of windows and walls. It means the ratio of the total area of ​​the transparent part of the window and the balcony door of the whole building wall to the total area of ​​the outer wall surface of the whole building. The area of ​​the window here emphasizes the area of ​​the transparent part, ie the area of ​​the partial window with the lighting function, if the back of the window is provided with a wall or the screen should not be included in the window area.
Generally, the heat transfer resistance of a window is much smaller than the heat transfer resistance of the wall. Therefore, the cold and heat consumption of the building increase with the increase of the area ratio of the window wall. On the contrary, the area of ​​the window wall is smaller than the design, and the heat is smaller. The smaller the loss, the better the energy-saving effect. In general, solar radiation intensity and solar radiation rate are different in different orientations, solar radiation heat obtained by windows is also different, solar radiation intensity and sunshine rate in the south and north direction are high, and solar radiation heat obtained by windows is more. GB50176-1993 “Civil Building Thermal Design Code†stipulates that when the wall is designed with a small heat transfer resistance, the area ratio of the facing windows and walls is: the north direction is less than 0.20; the east and west directions are not more than 0.25 (a single window ) or 0.30 (double window); southward not more than 0.35.
2. Use a suitable window type to reduce heat convection
Windows and doors are important elements that affect energy performance. The commonly used window type is generally a sliding window, a flat window, and the energy saving effect of the sliding window is poor, while the energy saving effect of the sliding window is superior. The sliding window slides back and forth on the sliding rails of the window frame. The upper part has a larger space, the lower part has the gap between the pulleys, the window fan forms a clear convection exchange between the upper and lower, and the convection of the hot and cold air forms a large heat loss. At this time, no matter what The heat-insulated profiles do not achieve the energy-saving effect of window frames.
Between the sash and the window frame of the casement window, there is generally a rubber sealing layer. After the window sash is closed, the sealing rubber layer is pressed tightly. There is almost no void, and it is difficult to form convection. The heat loss is mainly caused by the glass, window sash and window frame profile itself. Heat conduction, radiant heat dissipation and air infiltration at the contact position of the sash and the window frame, and air leakage between the window frame and the wall.
Generally, the heat insulation performance of the casement window is higher than about 20% of the sliding window, because the cold air permeation loss of the window occupies a certain proportion (about 10% to 30%) of the total window heat loss, and the flat window has high airtightness. To push and pull windows 1 to 2 levels, so from the perspective of energy conservation, we should try to use casement windows.
3. Reasonable selection of insulating glass, control of radiant heat
In the window, the glass area accounts for 65% to 75% of the window area. It mainly causes the loss of energy through heat radiation. Therefore, when we select the building window glass, we have to choose a reasonable glass to control the radiation passing through the windows and doors. Heat, thus ensuring the energy efficiency of the entire building.
Energy efficiency of glass is evaluated by heat transfer coefficient. The smaller the heat transfer coefficient, the better the heat preservation performance and the higher the energy saving. The larger the heat transfer coefficient, the worse the heat insulation performance and the lower the energy saving. Different types of glass have different heat transfer properties, as shown in Table 1: Table 1 Common Glass Heat Transfer Coefficients (W/?.K) Table 1 Common Glass Heat Transfer Coefficients (W/?.K)
It can be seen from Table 1 that the monolithic glass has a high heat transfer coefficient and is not suitable for energy-saving doors and windows. The energy saving performance of hollow glass is better than that of single glass, and the energy saving performance of Low-E hollow glass is better.
Hollow glass refers to two or more pieces of flat glass which are separated by a spacer frame and sealed with a sealant to form a dry gas space between the glass layers. Due to the fact that a certain thickness is formed between the two sheets of glass and the flow of air or other gas layers is limited to reduce the convection and conduction heat transfer of the glass, it has a better thermal insulation capability.
Low-e glass (also known as Low-E glass) has good spectral selectivity, and on the basis of a large amount of visible light, it can block a considerable portion of infrared rays from entering the room. Especially, far-infrared rays are reflected almost completely by the glass without passing through the glass. It not only maintains high light transmittance, but also reduces indoor heat load to a great extent. It can block the transmission of heat through the glass and has a good energy-saving effect.
The hollow product made of LOW-E glass can increase the heat-resisting performance by more than one to two times than ordinary insulating glass, and has excellent solar control and thermal control capability. In the hot summer season, when the outdoor temperature is higher than the indoor temperature, the LOW-E insulating glass can prevent the outdoor heat from radiating into the room. In the cold winter, the indoor temperature is higher than the outdoor temperature. The LOW-E insulating glass can prevent the indoor temperature from radiating to the outside, and Prevents the loss of diffusion of temperature. LOW-E insulating glass has a good thermal insulation effect, making it an ideal choice for energy-saving door and window glass.
4Select suitable window frame materials to reduce heat conduction
The window profile accounts for about 15% to 30% of the area of ​​the outer window opening, and is another weak link in the energy loss of the outer window of the building. The heat loss through the window frame accounts for a certain proportion of the total heat loss of the window. Therefore, the window The use of profiles is also crucial. The thermal conductivity of the window frame material determines the different energy consumption of the doors and windows. The larger the thermal conductivity, the stronger the heat transfer capacity and the greater the energy consumption. China's commonly used window frame materials are aluminum alloy, PVC plastic, steel, heat-insulating aluminum alloy, etc. Table 2 lists the thermal conductivity of the four kinds of window frame materials.
It can be known from the table that the thermal conductivity of PVC plastic material is low, which is conducive to heat insulation, but its strength, durability, fire prevention, etc. are not equal to aluminum alloy materials. From the perspective of environmental protection, the plastic profiles will emit toxic fumes when sawing. In case of fire, toxic gas “dioxin†is emitted, which is not environmentally friendly and is not recommended. The thermal conductivity of steel is very large and the heat transfer is very fast, which is not conducive to energy saving. Aluminium alloys have good reflectivity to ultraviolet, visible and infrared rays. The reflectivity of the surface is related to the surface state and color. The reflectivity to thermal radiation is as high as 90%. This is very favorable for blocking solar radiant heat. However, aluminum alloys have high thermal conductivity and are not conducive to energy saving.
In order to avoid the insufficiency of aluminum alloy, a heat-insulating aluminum alloy profile was developed. The principle of the aluminum alloy heat-insulating profile is to insulate the aluminum in the middle and break the aluminum profile to form a broken bridge, effectively preventing the conduction of heat. It retains the advantages of aluminum profiles, but also greatly reduces the aluminum profile heat transfer coefficient, energy saving effect is better, is a better choice for energy saving doors and windows.
There are two main production methods of heat insulation profiles. One is the use of heat insulation strips and aluminum profiles, and the “insulation bridge†is formed through mechanical splines, strips, and rolling processes. These are called heat insulation profiles. "Type"; the other is the insulation material poured into the aluminum alloy insulation chamber, after curing, removal of broken bridge metal and other processes to form a "heat insulation bridge", known as "casting" insulation profiles. The inside and outside surfaces of the heat insulation profile may be profiles of different sections, or may be different color profiles of different surface treatment methods.
However, due to the influence of the region and the climate, the difference between the linear expansion coefficient of the heat insulation material and the aluminum profile is avoided, and a large stress and gap are generated between the two in the thermal expansion and contraction; at the same time, the heat insulation material and the aluminum profile are combined. In one, on the doors and windows, the same force as aluminum. Therefore, it is required that the heat insulation material must also have the tensile strength, bending strength, expansion coefficient and elastic modulus close to the aluminum alloy profile, otherwise the heat-insulating bridge may be broken and destroyed.
5 Improve the airtightness of doors and windows and reduce air convection heat transfer
The airtightness of doors and windows refers to the ability to block air penetration when doors and windows are closed. The level of airtightness of doors and windows has a great impact on the loss of heat. Outdoor wind changes will have an adverse effect on room temperature. The higher the airtightness level, the less heat loss and the smaller the impact on room temperature. Therefore, improving the airtightness of doors and windows and reducing the penetration of cold air is also a way to improve the energy efficiency of windows.
The airtightness of windows in residential buildings and public buildings is specified in GB50176-1993 “Design Guidelines for Thermal Engineering of Civil Buildingsâ€: in the winter, the average outdoor wind speed in the area is greater than or equal to 3.0m/s, and it should not be low for 1 to 6-story buildings. In the current national standard "classification of air permeability performance of external windows and detection methods" GB7107 class III level; for 7 ~ 30-story buildings, should not be lower than the above-mentioned standard level II; in the winter outdoor average wind speed is less than 3.0 In the m/s area, the 1 to 6-story building should not be lower than the VI level specified in the above standard; for the 7 to 30-story building, it should not be lower than the level III specified in the above standard.
The air penetration is mainly between the window frame and the sash, between the sash frame and the glass, and between the window frame and the wall. The use of an ideal sealing strip can greatly reduce the air infiltration between the sash and the sash, and between the sash and the glass. The sealing strip is divided into rubber strips, plastic strips or rubber and plastics; the strips, brushes and sheets are in shape; the fixing methods include sticking, pressing or nailing. The sealing strip must have sufficient tensile strength, good elasticity, good temperature resistance and aging resistance, and the cross-section structure size must match the window and door profile.
Because the poor quality of the plastic strip is poor in resistance to aging, long-term exposure to the sun, the strip becomes harder after aging, loses its elasticity, and is easy to fall off. Not only is the sealing performance poor, but it also causes the glass to loosen and create safety hazards. The quality of the opening sealing material directly affects the seal between the window frame and the wall, which not only affects the heat insulation and energy saving effect of the house, but also relates to the waterproof performance of the wall. Therefore, the hole sealing material must also be selected correctly.
The gap between the four sides of the door and window frame and the wall is usually filled with polyurethane foam. This material not only has a filling effect, but also has a good seal insulation and thermal insulation performance, in addition to the application of more sealing materials There are silicone, EPDM rubber strips. When the sealing performance of windows does not meet the requirements of energy-saving standards, appropriate sealing measures should be taken, such as sealing strips or sealants made of rubber, felt, etc., at the gaps to improve the airtightness of the windows.
6 Conclusion
As China's building energy efficiency standards have been introduced, energy-saving doors and windows are increasingly favored by the market. In recent years, China has done a lot of work on the research and development of energy-saving doors and windows and the introduction of technology. Overall, there has been a significant increase in energy efficiency in doors and windows, but there is still a big gap compared with advanced countries. We should learn from foreign advanced technologies and combine China's national conditions for actual research, improve the quality of doors and windows, in order to meet the needs of building energy conservation development.
The above contents are all based on the problems encountered by the trainees during their actual work. For reference, if any problems occur, please communicate and correct them promptly.
Magnetic stripe & Door Sealing stripe
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