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[China Glass Net] The glass curtain wall is a new type of wall in the contemporary. It gives the building a large feature that organically unifies the elements of architectural aesthetics, architectural functions, building energy conservation and building structure. The buildings are presented from different angles. Different shades give the dynamic beauty with the changes of sunlight, moonlight and light. The glass curtain wall is the product of the development of modern science and technology and is also a prominent feature of the modern high-rise building era. The energy-saving way of the glass curtain wall is usually to reduce the structural heat transfer coefficient by using coated glass, Low-E glass, heat-reflecting glass, insulating glass and heat-breaking bridge aluminum profiles, eliminating the "heat bridge" of the structural system and reducing the heat loss of air permeation. Improve sealing and so on. The project uses heat-dissipating aluminum profiles and hollow glass structures filled with argon to achieve heat-dissipation and energy-saving, reducing the heat loss through conduction and reducing the possibility of indoor moisture condensing on the surface of aluminum profiles due to supersaturation. Therefore, the use of aluminum alloy glass curtain wall in high-rise buildings has received extensive attention from the industry.
1. Application and development of aluminum alloy glass curtain wall for high-rise buildings
The ventilated curtain wall consisting of two inner and outer glass curtain walls is also called double-layer curtain wall, breathing curtain wall and hot channel curtain wall. A ventilation and ventilation layer is formed between the inner and outer curtain walls. Due to the circulation or circulation of air in the ventilation layer, the temperature of the inner curtain wall is close to the indoor temperature and the temperature difference is reduced, which saves energy compared with the traditional curtain wall heating. %~52%, saving energy by 38%~60% during cooling. With the continuous development of China's economic construction, building curtain wall as a high-tech product in China's construction industry has developed by leaps and bounds. With the development of aluminum alloy hidden frame curtain wall, the aluminum curtain wall has also sprung up. The use of aluminum alloy glass curtain wall in the curtain wall project makes the high-rise buildings in China more colorful and colorful, forming various colors and forming a beautiful curtain wall pattern. A curtain wall made of aluminum is a form of building curtain wall. It is mostly used for wall covering and non-lighting walls instead of mosaic and glazed tiles. At present, aluminum sheets that can be used for curtain wall engineering in the domestic construction market are generally of several types, such as single-layer aluminum sheets, composite aluminum sheets, and honeycomb aluminum sheets. Composite aluminum sheets are currently widely used.
The heat transfer process of glass curtain wall can be roughly divided into three ways: First, heat transfer of glass and aluminum alloy (stainless steel) metal sash: heat transfer through a single layer of glass, heat transfer through the metal sash, reduce radiation through the coating layer of glass Heat exchange; the second is the heat exchange between the inner surface of the curtain wall and the indoor air and the indoor environment: convective heat transfer between the inner surface and the indoor air, radiation heat exchange between the inner surface and the indoor environment; third, the outer surface of the glass curtain wall and the surrounding air Heat exchange with the external environment; convective heat transfer between the outer surface and the surrounding air, radiation heat exchange between the outer surface and the external environment, and long-wave radiation exchange between the outer surface and the space. Fourth, the ordinary glass curtain wall adopts the beam-column structure of single-layer glass and aluminum alloy profiles, while the energy-saving glass curtain wall should be considered from the above three ways: the former approach (heat conduction) has a great influence on the node design, and the thermal conductivity of the glass is Insulating glass is used in design; for the thermal conductivity of aluminum frame, nylon 66 and other structural plastics are used in the design to form a “broken bridgeâ€, which can increase the thermal resistance and reduce heat conduction, thus designing a heat-insulating curtain wall. On this basis, consider the second way (heat convection) and the third way (thermal radiation), using double-layer LOW-E glass in the structure, and convection openings at the upper and lower ends to design a dynamic curtain wall.
The building curtain wall is an integral part of the building envelope structure. It is a part of building heat exchange and heat conduction, which is more sensitive. The glass is an important part of the building curtain wall. The various materials of the building exterior wall are thinner and easier to pass. Hot materials, so to save energy, it is necessary to change the thermal performance of the glass. The insulating glass is composed of two or more pieces of glass. The glass is separated by a hollow aluminum tube filled with a desiccant inside, and the hollow part is filled with dry air or inert gas, and sealed with butyl rubber, polysulfide rubber or structural adhesive. Under certain conditions, the thermal insulation performance of the insulating glass is better than that of the general concrete wall. The ordinary double-layer insulating glass has a heat transfer coefficient of about 30% smaller than that of the single-layer glass, and the reflective hollow glass has a smaller heat transfer coefficient than the single-layer glass. About %, at the same time, the insulating glass has excellent sound insulation performance, and generally reduces the noise by 39 to 40 decibels. If two hollow glass sheets made of different thicknesses of glass are used, the sound insulation effect is better because the resonance is reduced. At this stage, most of the main measures to improve the energy-saving insulation performance of glass curtain wall are to use coated glass, Low-E glass, heat-reflecting glass, insulating glass and heat-insulating bridge aluminum profiles to reduce the structural heat transfer coefficient K and eliminate the structural system. Bridge", reducing air permeable heat loss, reducing the area of ​​the sash, and improving its sealing.
The intelligent curtain wall is an extension of the ventilated curtain wall. It is based on the intelligent building. The building supporting technology (warm, heat, light, electricity) is moderately controlled. The indoor air, temperature and light are effectively adjusted by the computer, and the building energy consumption is only equivalent. 30% of the traditional curtain wall. The basic unit of the photoelectric curtain wall is a photovoltaic panel. The photovoltaic panel is a battery array composed of a plurality of photovoltaic cells in series and parallel. The battery array is placed in two layers of glass and thermoformed with a cast resin, on the back of the photovoltaic panel. Junction boxes and wires, so that solar energy can be converted into electricity for people to use. In general, the columns and beams of such curtain walls are made of insulated aluminum profiles. In order to reduce the heat loss and energy consumption of heating and heating in winter, in order to reduce the heat ingress and energy consumption of air conditioning and refrigeration in summer, the development trend of thermal design of glass curtain wall is to pursue the greenhouse effect for the curtain wall with heating and heating. For the curtain wall dominated by air conditioning and refrigeration to achieve the effect of cold room, no matter what kind of curtain wall will pursue the rational use of solar energy. Dynamic curtain wall (also known as hot channel curtain wall, double-layer ventilation curtain wall) is a good development direction. The photoelectric curtain wall composed of photovoltaic panel system and curtain wall system is also an application development direction of actively utilizing solar energy, and comprehensively uses light energy and heat energy. The intelligent glass curtain wall of electric energy is an ideal development direction. China's building energy consumption is two to three times that of developed countries with the same climatic conditions. In the process of building a well-off society in an all-round way, the task of energy conservation and emission reduction is very arduous. Building energy conservation is the basis for improving residential comfort and reducing the cost of use. It is also an urgent requirement for sustainable development. Only by putting resources and reducing energy consumption in a prominent position can we promote the construction of a harmonious society.
2. Thermal performance and energy saving measures of glass curtain wall
As the building exterior structure, the glass curtain wall has heat loss of heat transfer and cold air penetration, which accounts for 40% to 50% of the total energy consumption of the building. If the glass curtain wall adopts a reasonable structure, the energy loss can be greatly reduced. The influence of glass curtain wall on the energy consumption of existing buildings mainly has two aspects: First, the thermal performance of the glass curtain wall affects the heating in winter and the indoor and outdoor temperature difference heat transfer in summer. Second, the transparent material of the curtain wall (such as glass) is heated by the solar radiation and causes heat in the building.
The thermal performance of the glass curtain wall mainly includes: heat transfer coefficient K, shading coefficient Sc and anti-condensation coefficient. The heat transfer coefficient K value refers to the amount of heat transfer from the air to the air due to the heat transfer of the glass and the difference between the indoor and outdoor temperatures. The heat transfer process includes convection and heat conduction. The heat transfer coefficient is an important aspect of the thermal performance of the glass curtain wall. The insulation performance in the "Classification of Physical Performance of Building Curtain Walls" is divided accordingly. The lower the K value, the lower the heat transfer amount through the glass. The shading coefficient of the glass curtain wall refers to the ratio of the heat of the solar radiation energy passing through the curtain wall glass to the heat passing through the 3 mm transparent glass under the same conditions. The smaller the Sc value, the better the performance of blocking direct sunlight radiation. Therefore, a lower K value and a smaller Sc value can effectively reduce the three heat transfer. According to the experimental results, the ability of heat conduction and convection heat transfer can be measured by the heat transfer coefficient. The radiation heat transfer capacity can be controlled by the shading system, and the heat transfer of the building is the result of the combination of the above three methods. The energy-saving design of the glass curtain wall is to design reasonable control means to achieve energy-saving purposes. The thermal performance of the glass curtain wall can be achieved by controlling heat transfer and increasing occlusion.
According to the energy-saving design standard, the thermal performance requirements of the transparent glass curtain wall are the same as those of the window, and the heat transfer coefficient and the shading coefficient should be determined according to the proportion of the area occupied by the outer wall. The larger the area occupied by the transparent glass, the smaller the heat transfer coefficient and the shading coefficient requirement. Since the area of ​​the transparent glass should not be more than 70% of the area of ​​the external wall, and there are structural structural beams and columns behind the glass curtain wall, it is necessary to set a firewall of 800 mm height between the lower layers of the glass curtain wall required by the fire protection specification. We can design the glass curtain wall of the two parts into opaque glass or other materials. If the area of ​​the two parts is less than 30% of the entire glass curtain wall, it can be calculated and designed through the architect design process. Increasing the proportion of opaque glass curtain wall, thus adjusting the system's virtual and real proportion of the entire curtain wall, so that the energy saving requirements of the entire glass curtain wall are satisfied.
As the window to wall ratio (the area ratio of the transparent portion of the curtain wall and the non-transparent portion) increases, the heat gain through the transparent glass curtain wall increases sharply, and the air conditioning cooling load also increases sharply. Due to different processing techniques, glass can be divided into ordinary flat glass, heat absorbing glass, heat reflecting glass, low radiant glass and some functional glass with special purpose. The heat transfer coefficients of various glass are different. The effect of curtain wall profiles on the thermal performance of curtain walls: whether it is bright frame, hidden frame, hanging type, point-supported or unitized glass curtain wall, its structural frame, especially the performance of the joint profile, is the thermal performance of the glass curtain wall. Have a certain impact.
The transparency of the glass can be used for indoor lighting and heating. The total amount of radiant energy transmitted through the glazing is determined by the local solar radiation intensity, the angle of incidence of sunlight and glass, and the nature of the glass material. When the angle between the incident angle ray and the glass normal exceeds 60 degrees, the reflectance is greatly increased. Summer heat radiation increases the air conditioning load and has a heating effect in winter. Air infiltration is caused by the difference in air pressure between the inside and outside of the building caused by wind pressure and hot pressing, and the gaps or holes existing in the building envelope are necessary for air infiltration. For existing curtain wall buildings, air penetration is caused by loose parts. Hot air infiltration in summer increases the air conditioning load. In winter, the infiltration of cold air will increase the heat load. For the hot summer and cold winter areas, the outdoor outdoor air design temperature is 0 °C, and the indoor and outdoor temperature difference is 20 °C. The increased heat load cannot be ignored.
Reducing the window-to-wall ratio of buildings is a more direct and effective way to reduce the energy consumption of buildings. In actual engineering, the requirements of appearance and lighting should be comprehensively considered. According to the requirements of design specifications, the performance of glass curtain walls should be selected to suit the appropriate window-to-wall ratio. The use of energy-saving glass to improve the thermal resistance of the glass and reduce the heat transfer coefficient of the glass is a relatively straightforward method to reduce the energy consumption of the glass. In order to improve the thermal resistance of the frame, the heat-dissipation bridge type energy-saving profile is selected, the glass curtain wall shading system is installed, the sunshade system shields the solar radiation, reduces the influence of solar radiation on the indoor environment, enriches the building facade, and has various types of glass with substantially the same heat transfer coefficient. Curtain walls, improving the airtight performance of the curtain wall and reducing air convection heat transfer are also critical to reducing the energy consumption of the building curtain wall. To reduce the air leakage of various uncontrollable enclosures, the use of controlled ventilation measures is conducive to increasing fresh air supply, improving indoor air quality and reducing building energy consumption. In addition to the glass panels, the metal profiles of the glass curtain wall are also two important factors that affect the appearance and energy saving of the entire curtain wall system. In the frame glass curtain wall, the weighted average heat transfer coefficient in the glass and curtain wall structure should be taken as the heat transfer coefficient of the glass curtain wall. It seems that the heat transfer coefficient of the full hidden frame glass curtain wall is closer to the heat transfer coefficient of the glass panel, because although there is a structural frame, since it is hidden behind the glass panel, it has less influence on the heat transfer coefficient of the entire curtain wall, but From the perspective of the safety of the curtain wall, the exposed frame is more reliable, and the heat-frame of the metal frame type is reduced by the bright frame of the segment.
The glass curtain wall thermal bridge is part of the structure, and its overall thermal insulation capacity is degraded due to its good thermal conductivity. In the ordinary glass curtain wall, the aluminum alloy frame is the thermal bridge of the glass curtain wall, and its thermal conductivity is hundreds of times that of the glass. The cold bridge is a unique thermal bridge. The structure or component that is not heat-treated is able to conduct heat away faster than the surrounding area and the inside surface of the bridge, so its temperature is lower. This type of thermal bridge, Commonly known as "cold bridge." The aluminum profile that has not been heat-treated in winter is a cold bridge. The indoor water vapor forms on the same surface of the cold bridge and the surrounding condensed water. The presence of condensed water increases the difficulty of structural treatment and provides mildew on the interior decorative surface of the curtain wall. condition. In today's public buildings, exhibition buildings and sports buildings generally use large-area glass curtain walls for display functions and aesthetic requirements. Since glass is a good conductor of heat, hollow glass or Low-E glass is mostly used for energy saving. If an aluminum alloy frame with a common glass curtain wall has a heat transfer coefficient of 203.00 W/m2.K, the aluminum alloy frame will form a heat bridge to generate energy.
The shading system of the glass curtain wall is one of the direct ways to directly reduce the shading coefficient of the curtain wall. In addition to selecting the glass material with different material properties, it is also possible to reduce the shading coefficient by additionally providing a shading system. This has also become an important form of facade. Such a system of glass curtain wall can be divided into three ways: external shading system, double-glazed curtain wall shading system and built-in shading system. Glass curtain walls are becoming more and more widely used in today's buildings. As glass curtain wall technology is further developed and improved, its position in architectural design will become more important. Architects should use appropriate design forms to consider the current form of glass while taking into account its thermal performance, providing energy-saving efficiency according to the building, in line with China's "energy-saving emission reduction" policy and energy conservation.
3. Problems and countermeasures in the promotion and application of broken aluminum profiles in building curtain wall
The building curtain wall is an integral part of the building envelope structure. It is the part where the building heat exchange and heat conduction are more active and sensitive. The aluminum profile is an important part of the building curtain wall, and it is easy to transfer heat in various materials of the building exterior wall. Materials, so to ensure energy savings throughout the building curtain wall, it is necessary to change the thermal performance of aluminum profiles. The heat-dissipating aluminum profile consists of an aluminum profile and an intermediate insulation material, the intermediate insulation material mainly functions to prevent heat conduction. The foreign "breaking heat bridge" technology is to remove a part of the heat conduction path of the high thermal conductivity aluminum profile, and replace the material with low thermal conductivity, and connect the aluminum profiles at different ends of different ambient temperatures to obtain the same. The overall thermal conductivity of the composite material is bound to be greatly reduced, the thermal resistance value is greatly improved, and the heat lost by the aluminum profile is greatly reduced. This type of isolation is called “breaking heat bridge†or “broken bridgeâ€. The aluminum alloy profile with this type of isolation is called “insulated bridge aluminum profile†or “broken bridge aluminum profileâ€, spacer. It is called “breaking heat (cold) bridge material†or “breaking heat (cold) bridge†or “broken bridgeâ€. Due to the adiabatic effect of the heat-breaking cold bridge, when the outdoor end of the profile is below zero, the indoor end remains at a normal temperature. There is a bond between the cold-cold bridge and the aluminum alloy so that the two can interact (transmitting forces and deformations). This ensures that the heat-dissipating cold bridge in the component under the load can coordinate deformation and joint force with the aluminum alloy profiles that are engaged on both sides. That is, the aluminum alloy profile that can be engaged with the two sides of the thermal cooling bridge does not have a relative displacement under load. The temperature linear expansion coefficient of the cold-cold bridge and the aluminum alloy is relatively close. When the temperature changes, there is no large relative deformation between the two, and the adhesion is destroyed. This is a prerequisite for the existence of such a composite material. The heat-dissipating cold bridge aluminum profile effectively improves the thermal insulation performance of the curtain wall. The ability of the cold-brassed aluminum profile to withstand high temperatures is also high. However, it cannot be sprayed with fluorocarbon, so the heat-cooled cold-bridge aluminum profile that needs to be sprayed should be sprayed and then composited.
Nowadays, the use of heat-dissipating aluminum profiles in the field of curtain wall is more and more extensive, but there are also some limitations in the glass curtain wall, such as light pollution and high energy consumption. However, with the continuous emergence of new materials and new technologies, these problems are gradually being incorporated into the comprehensive research system of architectural modeling, building materials and building energy conservation, and are discussed in depth as a whole design problem. There are three measures for preventing the reflection of the glass curtain wall: First, the material should be rough, such as frosted glass, and should not be used with full reflective glass; second, pay attention to the angle of installation of the glass curtain wall, try not to use glass in concave and inclined buildings. The curtain wall; the third is to install double-glazed glass in the glass curtain wall, and the black light-absorbing material is attached to the inner glass, so that the light can be absorbed in a large amount, and the reflected light is prevented from affecting the public.
The heat-dissipating aluminum-plastic composite aluminum profile solves the problem of high heat transfer coefficient of ordinary building aluminum profiles, and fundamentally improves the moisturizing and heat-insulating properties of aluminum doors and windows and aluminum curtain walls. It has made it possible to promote the application of high-efficiency and energy-saving, high-grade luxury aluminum doors and windows, and opened up new market development space. However, the quality and safety of the heat-resistant aluminum-plastic composite building aluminum profiles are very prominent. Mainly manifested in: the safety and reliability of the quality of the thermal insulation layer engineering plastics, as well as the mechanical properties and mechanical strength stability of the aluminum-plastic composite. At present, the research on the heat-dissipating plastic composite profiles processed by the injection molding method or the inlaid strip process is still deepening. The influence of the thermal insulation layer on the performance of the architectural aluminum profiles and the combined mechanical properties of the composite materials will be improved. The heat-dissipating aluminum profile is applied to the window and the exposed glass curtain wall. In order to achieve the equivalent thermal insulation and heat insulation effect, the heat-dissipating aluminum profile is generally used together with the insulating glass. For the framed glass curtain wall, since the aluminum alloy inside and outside is integrated or directly contacted, the aluminum alloy has a large thermal conductivity, and the heat preservation and heat insulation effects are not good. Therefore, the exposed glass curtain wall adopts hollow glass to cut the hot aluminum profile, which has obvious heat preservation and heat insulation effects. For the hidden frame glass curtain wall, the direct contact between the curtain wall structure and the outdoor is hollow glass, between the glass and the aluminum profile is a silicone structural adhesive, and the inner side of the structural adhesive is an aluminum profile. Generally, the thermal conductivity of the coated hollow glass is 2.3 ≤ K ≤ 3.2. If the hollow glass made by offline LOW-E coating is 1.4 ≤ K ≤ 1.8, the heat preservation and heat insulation effects are already good, and the structural adhesive is also a low thermal conductive material, and also has good. Thermal insulation. Theoretical analysis and experimental results show that the hidden frame glass curtain wall does not have to use heat-dissipating aluminum alloy profiles.
At present, in order to reduce costs, some engineering projects use PVC broken bars to replace nylon 66 broken bars. Because the linear expansion coefficient of PVC is far from the linear expansion coefficient of aluminum alloy, and its strength is low (only about 30N/mm2), poor heat resistance (80 °C), poor anti-aging performance, etc. After the actual installation and use of the heat-dissipating aluminum profile, the PVC heat-insulating strip may loosen or even completely detach from the aluminum profile due to thermal expansion and contraction, which may cause looseness and deformation, thereby destroying airtightness. And water tightness, and the overall result is loose and detached. The hot strip is also a function of the broken glass curtain wall. At the same time of carrying the force, the heat-insulating strip also functions as a sealing and transferring. If the thermal expansion coefficient of the aluminum profile matrix by the mechanical composite rolling is inconsistent, then under the condition of uneven heat and cold, the deformation will inevitably occur, and the aluminum profile and the heat insulation strip cannot be guaranteed. A completely independent combination of "spin-and-synchronization" will inevitably lead to loosening of the hot strip in the aluminum profile groove or deformation stress on the heat-dissipating aluminum profile. In addition, the hot strip is an important part of the heat-dissipating aluminum profile, and its dimensional accuracy directly determines the dimensional accuracy of the composite heat-dissipating aluminum profile. The assembly precision of the glass curtain wall is 0.2-0.3mm. In order to ensure the wind-resistant, airtight and water-tightness of the heat-insulating glass curtain wall, the residual error is considered. If the shape of the heat-breaking strip itself cannot be strictly controlled at 0.1 With an accuracy of less than mm, it is difficult to ensure the assembly accuracy of the overall glass curtain wall.
The aluminum alloy building profile GB5237-2004 has been implemented, the new standard has increased the standard for heat-insulating profiles, and the construction industry standard for the heat-breaking strip will also be introduced. With the reference of standardized production operation, all aspects will pay full attention to the manufacture and installation of heat-dissipating glass curtain wall, and will further promote the standardized development of the heat-insulating glass curtain wall market.
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