Discussion on sunshade and energy saving technolog

2022-08-04
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Discussion on sun shading and energy saving technology of glass curtain wall

Abstract: the importance of energy saving of glass curtain wall as building envelope; The necessity, function and effect of glass curtain wall shading; Form and structure design of sunshade; Intelligent design of sunshade system

key words: building energy conservation; External shading and glass shading; Glare

with the wide application of glass curtain walls in China, the national use volume last year has exceeded 1.5 million m2. Metal glass curtain wall has the advantages of light weight, non combustibility, shock resistance, rapid construction and so on. Under the premise of modern urban high-rise, fire prevention, shock resistance and construction safety, it has become one of the main forces of high-rise buildings in the future. The metal glass curtain wall can reduce the use of a large number of steel bars and concrete for the traditional concrete exterior wall, which is of great help to reduce the use of high energy consuming building materials to save energy and resources; But at the same time, as the external enclosure structure of the building, the glass curtain wall is the most active and sensitive part of the building in terms of heat exchange and heat conduction. It is 5 ~ 6 times the heat loss of the traditional wall. The energy consumption of the curtain wall accounts for about 40% of the energy consumption of the whole building. Therefore, the energy conservation of the curtain wall plays an extremely important role

1. The necessity of shading the glass curtain wall

the energy-saving design of the outer envelope of the building is linked by factors such as window opening, orientation, shading and thermal insulation materials, which affect the energy consumption of the building. The Seraya Research Office in Taiwan has studied the peripheral protective structure of office buildings in Taiwan, and analyzed the energy consumption of various elements of the building's external protective structure. The analysis results are as follows:

from the above, it can be concluded that:

1.1 the window opening rate of the external wall is the most important factor for external wall energy conservation. Reducing the window area ratio is the most important means to save energy, but reducing the window area ratio must also take into account to ensure proper natural lighting and avoid the psychological sense of closure. However, for the glass curtain wall that pursues the transparent effect, the energy-saving requirements can only be achieved by reducing the open window area and strengthening the heat insulation design in the opaque area

1.2 external shading and glass shading are the second important factor of external wall energy saving. Both the glass material and the external sunshade affect the shading rate, but the installation of sunshades, sunshades and other external sunshades is far more effective than changing the glass material. Reflective glass and heat absorbing glass with high reflectivity can be selected as the glass material (only reflective glass with too much reflectivity will cause glare pollution)

1.3 the building orientation factor is the third element of the external wall energy-saving design (accounting for 12%). Large area glass curtain wall shall be protected from exposure to sunlight from the east to the West. The long direction of the building shall face the north-south direction. In China, with the development of market economy, building energy conservation is an urgent need for China's sustainable economic and social development. The awareness of energy conservation and environmental protection of construction units and design units has also been continuously improved, and the requirements for energy conservation of glass curtain walls have also been continuously improved. At this stage, the main measures to improve the heat insulation performance of glass curtain walls include:

1.3.1 using coated glass, Low-E glass, heat reflective glass Insulating glass and other glass processing technologies to reduce the direct radiation of the sun through the glass

1.3.2 the application technology of high thermal resistance materials such as aluminum-plastic composites and heat break bridge profiles shall be adopted

the principle of the above thermal insulation measures is relatively simple, which greatly reduces the heat transfer coefficient of the glass curtain wall structure. These energy-saving measures have been widely used in buildings at this stage. Although the glass curtain wall building can achieve better heat insulation and energy saving effect by adopting shading measures, at this stage in China, all parties do not pay enough attention to it. The annual air conditioning power consumption of a poorly designed building with all glass curtain walls may be four times that of an ordinary concrete exterior wall building. Otherwise, the glass curtain will accelerate the wear of various parts of the hydraulic pressure. The service life of the wall will be as long as 50 years. Of course, its energy-saving effect is far better than that of short-lived air conditioners, refrigerators, boilers, etc. Therefore, the consumption rate of glass curtain wall should be gradually increased. The energy conservation of buildings is more important than that of other building products. Therefore, the development of shading technology for glass curtain wall is also one of the important means for building energy conservation, that is, large-scale manufacturing → large-scale customization → interconnected factories

2. The role and effect of shading

as the glass curtain wall is composed of glass and metal structure, the glass surface has strong heat exchange and high heat transmittance, so it has a great impact on the indoor thermal conditions. In summer, the sun shines through the glass into the room, which is the main cause of indoor overheating. Especially in the hot areas in the south, if the human body is directly exposed to the sun again, it will feel hot and uncomfortable. The sun shading system on the glass curtain wall can minimize the direct sunlight exposure, thus avoiding indoor overheating. It is one of the main measures for building heat protection in hot areas. After sunshade is set, it will have the following functions and effects:

2.1 sunshade effect on solar radiation. The thermal insulation performance of the peripheral protective structure is affected by many factors, among which the most influential index is the shading coefficient. Generally speaking, the shading coefficient is controlled by the characteristics of the material itself and the environment. Sunshade coefficient is the ratio of solar radiation through the enclosure with sunshade measures and the enclosure without sunshade measures. The smaller the shading coefficient, the smaller the solar radiation heat through the outer enclosure structure, and the better the heat protection effect. The measured shading coefficients of the main windows in Guangzhou are 17% in the west, 45% in the South and 60% in the north. It can be seen that shading has a considerable effect on shielding the solar radiant heat, and the shading measures for glass curtain wall buildings are more effective

2.2 the effect of shading on indoor temperature. Shading has an obvious effect on preventing the rise of indoor temperature. The test observation in a west facing room in Guangzhou shows that the maximum difference between room temperature with and without shading is 20 C with an average difference of 1.40 C under the condition of closed windows. Moreover, when there is shading, the room temperature amplitude is small, the time delay of the maximum value at room temperature occurs, and the indoor temperature field is uniform. Therefore, shading can reduce the cooling load of air-conditioned rooms, so shading is one of the main measures to save electric energy for air-conditioned buildings

2.3 the effect of sunshine on daylighting when the total investment is within 50million euros. From the point of view of natural lighting, shading measures will block direct sunlight, prevent glare, make indoor illumination distribution more uniform, and contribute to the normal work of vision. For the surrounding environment, shading can disperse the reflected light of the glass (especially the coated glass) of the glass curtain wall, and avoid light pollution caused by large-area glass reflection. However, as the sun shading measures can block the light, the indoor illumination will be reduced, which is more unfavorable in rainy days. Therefore, full consideration should be given to the design of shading system to meet the requirements of indoor natural lighting as far as possible

2.4 effect of shading on building appearance. The sun shading system forms a light and shadow effect on the glass wall with the appearance of the glass curtain wall, reflecting the aesthetic effect of modern architectural art. Therefore, in the European architecture industry, the external shading system has been used as an active facade element, even called the double-layer facade form. One floor is the facade of the building itself, and the other floor is the facade form of dynamic shading state. This "dynamic" building image is not because of the intelligent design of the sun shading system for building curtain walls, but because the modern computer integration technology is adopted for the control system of the motor controlling the angle adjustment of the sun visor or the lifting and lowering of the sun visor. At present, domestic and foreign manufacturers have successfully developed: time motor control system and climate motor control system

3. To study the role and effect of sunshade system on building art and building technology, especially in building energy conservation and intelligence, we need our continuous development and research, so as to truly make the sunshade system of domestic building curtain wall keep pace with the times

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