The content of this article is compiled and published by the editorial department of China Curtain Wall Network:

1. Preface

　　The issue of energy shortage has become a globally recognized problem today. At the Vienna Conference on Science for Development held by the United Nations in 1979, energy was listed as one of the four major issues facing humanity: energy, food, population, and environment. At present, China's economy is in a period of rapid development, and energy demand is also growing rapidly. The contradiction between urban and rural construction and energy supply and demand is very prominent, especially in the construction and residential industries, which are major energy consumers. How to solve the problem of energy shortage? Currently, energy conservation is the top priority in addressing global energy issues, and building energy efficiency has become an important component of the national energy conservation strategy. Building energy efficiency includes energy-saving of new buildings and energy-saving renovation of existing buildings. The real major energy consumers of buildings are existing buildings, as there are a huge number of existing buildings and most of them do not have any energy-saving measures. Their insulation performance is poor, and the equipment system efficiency is low, resulting in serious waste of heating and cooling energy consumption. Most newly built buildings have achieved energy-saving targets through the efforts of the country in recent years, and some areas have started implementing energy-saving plans. So, energy-saving renovation of existing buildings is the key to building energy efficiency in China. If we only consider the energy-saving of new buildings in this regard and do not consider the energy-saving renovation of existing buildings, the actual effectiveness of building energy-saving can only be limited to a very small range. Therefore, it is urgent to strengthen the research on energy-saving renovation of existing buildings.

2. Current situation of existing buildings

　　It is relatively easy for new buildings to meet national building energy efficiency standards, as if the planning and design do not meet the requirements, relevant departments will not approve them. Due to different construction years and structural systems, the renovation modes of existing buildings vary greatly and involve many factors, making energy-saving renovation quite difficult. Therefore, it is necessary to increase investment in research from various aspects. Moreover, most existing buildings have poor insulation performance and low equipment system efficiency, resulting in serious waste of heating and cooling energy consumption. The key to energy-saving renovation of existing buildings is to improve the insulation and thermal insulation performance of the building's enclosure structure, reduce the energy consumption required for heating and cooling, and thus make the building's energy consumption meet the national energy-saving standards. So for the energy-saving renovation of existing buildings, it is necessary to carry out comprehensive energy-saving renovation of the building envelope structure and heating system. The existing buildings currently have the following main problems.

3. Energy saving principle of glass curtain wall

　　The use of glass curtain walls during construction has become a development trend in the modern construction industry. People mainly use glass curtain walls during construction because of their energy-saving function. Glass is a transparent material that allows for the transfer of thermal energy, primarily through convection, radiation (the term "radiation" is provided by industry encyclopedias), and conduction. When conducting heat transfer in glass, in addition to these three methods, it can also be achieved through direct transmission of sunlight. In order to better evaluate the process of energy transfer through glass, people can determine the number of joules transferred per unit area, unit temperature difference, and unit time. The larger the Joule number, the greater the energy loss of glass, which is particularly detrimental to energy conservation. In order to better test the energy-saving effect of glass curtain walls, the shading coefficient can also be studied. Under the same conditions, glass components and transparent glass are placed under sunlight, and the shading coefficient is determined by the ratio of solar radiation energy obtained from the industry encyclopedia. The smaller the shading coefficient, the better the energy-saving effect. When sunlight shines through glass into a room, a portion of it can pass directly through, while another portion is absorbed by the glass curtain wall and converted into heat energy, which directly enters the room. This will increase the heat energy of the house, which can raise the temperature inside the room.

4. Problems and Reasons in Building Glass Curtain Walls

　　4.1 Glass curtain walls have a certain sense of modernity and modernity, and the shape, structure, color and shape of glass curtain walls can be freely changed, making architects like to use glass curtain walls to increase the beauty of buildings. However, the energy consumption of glass curtain walls in construction projects has also caused some difficulties for our country. China is a major energy consuming country, and the rapid consumption of energy hinders the development of its economic construction. Nowadays, in Chinese cities, the energy consumption of buildings accounts for a quarter of the total energy consumption, and the energy consumption of public buildings accounts for the majority of the total energy consumption of buildings. Glass curtain walls in China are generally constructed in public buildings, and they cannot effectively utilize light resources. In summer, the heat absorbed by glass curtain walls increases due to high levels of solar radiation; In winter, due to the relatively low outdoor temperature, the heat dissipation rate of glass curtain walls accelerates, which forces an increase in the frequency of air conditioning use in both winter and summer seasons, resulting in a significant consumption of energy in China.

　　4.2 Nowadays, glass curtain walls can be seen everywhere in cities. Although they beautify the image of the city to a certain extent, they also generate a certain amount of light pollution. The glass curtain wall itself has a reflective effect on light, which affects the safe driving of vehicles on the road. The second issue is that glass curtain walls, when reflecting light for a long time, can have a certain impact on people's vision when they look at the white light formed by the reflection. At the same time, it can also cause certain diseases and affect people's mood. In some bustling metropolises, local city managers constantly receive complaints from citizens about light pollution.

　　4.3 The safety and quality performance of glass curtain walls have been continuously declining due to long-term exposure to rain, wind, and sunlight. Therefore, in some areas such as Shanghai, there have been many occurrences of curtain wall glass bursting (the term "bursting" is provided by the industry encyclopedia) and falling. The beauty of glass curtain walls no longer attracts the public's love for them. On the contrary, when walking below the glass curtain wall, they avoid it. The glass curtain wall, like a ticking time bomb, can explode on the heads of citizens at any time. Even if the design service life of glass curtain walls does not exceed 25 years, it will still put the energy consumption and safety hazards of glass curtain walls in an awkward state.

　　4.4 The occurrence of these problems with glass curtain walls is mostly due to material issues. The main material for building a glass curtain wall is glass material. As the main external maintenance part, the performance of glass directly affects the quality of the glass curtain wall. After formulating new energy-saving standards, some glass curtain wall technologies in our country cannot meet the new energy-saving standards.

　　4.5 In the process of constructing glass curtain walls, the sealing material used to connect the glass (the term "sealing material" is provided by an industry encyclopedia) is very important. The length of time the sealing material is weather resistant will have a certain impact on the length of time the glass curtain wall is used. When researchers conducted surveys on glass curtain walls in some cities, they found that some sealing materials used to connect the glass had already experienced a series of problems, such as cracking and damage to the tempered glass. The emergence of these phenomena has had a certain impact on the indoor environment of buildings and has also caused a significant amount of energy consumption.

5. Energy saving renovation method based on existing building glass curtain walls

　　5.1 When constructing glass curtain walls, a double-layer breathing curtain wall can be constructed. The establishment of a double-layer breathing curtain wall is mainly based on the phenomenon of utilizing the "chimney effect" in summer. The double-layer breathing curtain wall can provide natural ventilation and effectively reduce indoor temperature; At the same time, when constructing glass curtain walls, semi transparent rolling shutters can be installed. In summer, when the sunlight radiation is strong, the rolling shutters can be lowered. The rolling shutters have a certain blocking and reflecting effect, which can effectively eliminate most of the sunlight reflection. This can lower the indoor temperature of the building, reduce the frequency of using air conditioning for cooling, and promote the goal of energy conservation in China. In winter, the outer curtain wall ventilation openings of the double-layer breathing curtain wall can be closed. This way, the temperature inside the curtain wall gradually increases after receiving long-term sunlight exposure. Due to the closure of the ventilation openings, heat is difficult to dissipate, which reduces the temperature difference between indoor and outdoor to a certain extent. At the same time, the indoor temperature no longer transfers a large amount to the outside, playing a certain insulation effect. The application of double-layer glass curtain walls has achieved excellent sound insulation effect. The sound insulation effect of double-layer glass curtain walls is very strong. In the air layer between the glasses, the sound insulation performance of the glass curtain wall is hindered and improved to a certain extent. In some cities, noise pollution is very serious because the buildings in these cities cannot have good window ventilation, and using double-layer glass curtain walls is the best choice in such environments.

　　5.2 In glass curtain walls, sunlight exposure is also a major issue that needs to be addressed, therefore, certain shading techniques should be implemented for glass curtain walls. In some areas with hot summers and cold winters, building shading technology has been widely used. Sunshade technology is a very important building energy-saving technology, which can reflect or absorb solar heat in a timely manner, and has a certain control effect on indoor temperature. It can improve indoor comfort to a certain extent and reduce the energy consumption of air conditioning. The main methods of using sunshade technology in glass curtain walls are to first use horizontal sunshade technology. Throughout the year, the altitude and orientation of the sun constantly change and cycle, which requires designers to design according to the actual situation. At the maximum altitude angle of the sun, horizontal shading can effectively block the projected sunlight; Meanwhile, in winter, the maximum amount of sunlight can be introduced into the room. The second method is vertical shading, which is suitable for the northeast and northwest directions of buildings and can block oblique optical fibers; The third is comprehensive shading, which has a good covering effect on sunlight from various directions in buildings; The fourth option is to use a barrier style sunshade, which is suitable for areas with strong sunlight in the east-west direction. However, it may have a certain impact on people's visibility and indoor ventilation; Finally, there is the sunshade of the louver room, which can be adjusted from various angles according to people's needs, and has a certain promoting effect on sunshade, lighting and ventilation.

6. Material aspect

　　Use heat reflective LOW-E glass, insulated glass, etc. These glasses have been produced in China for a long time, but they are relatively expensive, so they were rarely used in glass curtain wall projects in the past. For example, insulating glass composed of heat reflective glass and transparent glass has better insulation performance than a thick brick wall. Use aluminum-plastic composite materials and heat-insulating profiles to make the crossbeam and column of the curtain wall (the term "crossbeam" is provided by the industry encyclopedia). When using insulated aluminum profiles, if the strip piercing process is used for production, the insulation material should be PUR material. In addition, applying film to existing curtain wall glass can effectively reduce energy consumption. The thermal insulation safety film currently available in the market (the term "safety film" is provided by an industry encyclopedia) can save energy by more than 15%.

7. Construction aspect

　　The use of sunshade facilities such as louvers, grilles, and sun visors can minimize direct sunlight exposure and avoid indoor overheating, thereby achieving better insulation and energy-saving effects. There are horizontal and vertical sunshade louvers, as well as split control, electric and adjustable louver systems. According to the architectural style and requirements, different forms and control methods of shading systems can be selected.

　　A ventilated curtain wall composed of two layers of inner and outer glass curtain walls, also known as a double-layer curtain wall, breathing curtain wall, or hot aisle curtain wall (the term "hot aisle curtain wall" is provided by the industry encyclopedia). A ventilation layer is formed between the inner and outer curtain walls. Due to the circulation or circulation of air in this ventilation layer, the temperature of the inner curtain wall is close to the indoor temperature, reducing the temperature difference. It saves 42% -52% of energy during heating and 38% -60% of energy during cooling compared to traditional curtain walls.

　　Intelligent curtain wall is an extension of ventilated curtain wall, which is based on intelligent buildings and moderately controls building supporting technologies (heating, heating, lighting, electricity). Through computer effective adjustment of indoor air, temperature, and light, its building energy consumption is only 30% of traditional curtain wall.

　　The basic unit of a photovoltaic curtain wall is the photovoltaic panel. The photovoltaic panel is a battery array composed of several photovoltaic cells connected in series or parallel. The battery array is placed in two layers of glass (transparent glass on the upper layer and any color on the lower layer) and heat cured with casting resin. The junction box and wires on the back of the photovoltaic panel can convert solar energy into electrical energy for people to use. In general, the columns and beams of this type of curtain wall are made of insulated aluminum profiles.

8. Conclusion

　　At present, in our country, the main focus is on using energy-saving technologies that are compatible with the level of economic development, and we must not pursue low energy consumption goals without considering economic costs. Simultaneously focusing on the research and development of renewable natural energy technologies such as solar energy, wind energy, and geothermal energy, reducing the cost of utilizing renewable energy, gradually promoting their application from large cities and economically developed regions to the whole country, and achieving the established goal of building energy conservation in China.