Taking China and Germany as examples, from the requirements and changes of building energy conservation in developed countries, look forward to the future development of door and window markets in developing countries.

1. The changes in China's national and local standards

In March 2023, the Department of Standards and Quotas of the Ministry of Housing and Urban-Rural Development of China requested the National Standardization Technical Committee of Curtain Wall Doors and Windows (hereinafter referred to as the "Standard Committee") to organize experts in the industry to form a research and development working group, mainly for the current performance of doors and windows in China. According to local conditions, improve the green indicators of China's door and window performance, greatly improve the heat insulation, sound insulation, airtight performance, and other indicators of China's doors and windows, so that the performance of China's doors and windows can reach the leading level in the same climate zone in the world (such as the doors and windows in Beijing in 2023 The thermal insulation performance reaches about 1.0 W/m²℃), and it is decided to use the energy-saving performance of doors and windows as a breakthrough to simultaneously improve the safety, durability, and comfort of doors and windows. The Standardization Committee immediately set up a working group on the development of key technical indicators of building doors and windows standards. After more than a year, the working group investigated, collected, and sorted out all the requirements of 33 advanced countries on the performance of doors and windows in the world, and completed the work. The report was submitted to the Department of Standards and Quotas of the Ministry of Housing and Urban-Rural Development, and it was planned to promote the substantial improvement of all performance indicators of doors and windows in China following the requirements of "one step in place and implementation of step by step".

Under the vigorous promotion of the Ministry of Housing and Urban-Rural Development, some provinces and cities in China have issued local technical regulations and regulations on doors and windows, and have improved various performance indicators of doors and windows. The provinces and cities that have been issued so far include Beijing, Shanghai, and Jiangsu, Zhejiang, Fujian, Hebei, etc. Provinces and cities that are in the stage of the organization or opinion solicitation include Tianjin, Anhui, Hubei, Hunan, etc. The most notable changes in these revised local standards can be summarized in the following points:

(1) The requirements for energy-saving indicators have been greatly improved. For example, Fujian requires the heat transfer coefficient of doors and windows to reach 3.0W/m²C;

(2) Put forward clear requirements for standardized doors and windows and systematic doors and windows;

(3) Put forward clear requirements for the installation process and construction of doors and windows;

(4) There are clear requirements for the durability and service life of doors and windows.

It is worth mentioning that Beijing's energy-saving index requires a direct increase from the current 75% energy-saving 1.5^2.0W/m²℃ to 1.1 W/m²℃, and the balance calculation method is canceled, that is to say, all doors and windows are converted into The energy-saving index of standard windows must meet the requirement of 1.1 W/m²℃, which is only high compared with the requirements of the Ministry of Construction that the energy-saving index of doors and windows in Beijing in 2023 should reach the level of Germany in the same period in 2018. Domestically, we have been talking about changes in the technical indicators of the German door and window market and changes in German standards for doors and windows. So, how does the German door and window market develop, what is the current market distribution and development trend? To answer these questions, LIJIANG Glass believes that it is necessary to first understand the types, prices, market share, and market evolution of doors and windows in the German market, to predict future changes in the Chinese market.

2. The Development and Evolution of the German Door and Window Market

In 2022, the German Door, Window and Curtain Wall Association VFF and the German Glass Association BF jointly published a report, which is divided into six parts, namely:

(1) Energy-saving performance of different types of windows;

(2) Germany's modernization potential;

(3) cost-effectiveness of new windows;

(4) the cost-effectiveness of investing in high quality rather than replacing minimum standards;

(5) Additional benefits of new windows;

(6) Significance of replacing windows.

The tables that are cited for this article are as follows, including Tables 1 to 3.

^{Table 1 The number of doors and windows in stock in the German market in 2021}

At what stage were these types of windows used in the entire historical cycle of door and window development in Germany? How do the doors and windows perform? As shown in Table 2.

^{Table 2 Heat transfer coefficient and solar heat gain factor SHGC of different windows}

So, in Germany, what are the market prices and market distribution of different types of doors and windows? Compared with the minimum performance requirements of the EU ENEV standard, are the doors and windows sold in the actual market the same as those in the domestic market, and only meet the standard requirements? Table 3 shows the differences between the types of doors and windows in Germany and the minimum standard requirements.

^{Table 3 Differences between German door and window types and comparative minimum standard requirements}

The replacement window market is in the industrial housing insulating glass (Uw=0.95W/m²K. Solar heat gain factor SHGC=62%) replaces the window f2K. Solar heat gain factor ~SHGC: 60% according to the ENEV standard)

From Table 3, we can know that the door and window products sold in the German market are about 10% higher than the minimum requirements of the EU standard ENEV in terms of price and performance. For example, the EU standard ENEV requires the energy-saving index of doors and windows to be L3W/m²K in 2016, while the U value of products sold in the German actual market (including the retail market and engineering market) is about 1.1W/m²K~1.2W/m²K. In addition, in the German market, the largest market share is PVC windows, accounting for about 57.8%, while the market share of aluminum alloy windows (all aluminum alloy windows in Germany are aluminum alloy with broken bridges, which will not be repeated in this article) 18%. This is related to the climatic conditions in Germany, the size of the window opening, the type of building, the height, and other factors. People who have been to Germany can see that the height of residential buildings in Germany is multi-story buildings, and the window openings are standard, and most of the windows used are single-frame single-leaf opening windows, so plastic windows are more common. Due to the large size of openings and large window grids in most commercial buildings, most of them use broken bridge aluminum alloy windows. As for the changes in the types of the entire door and window market, the types of glass configurations, and the market share since the implementation of building energy conservation in Germany in the 1970s, the survey report gives the different types of trends in the German construction market from 1977 to 2021. The evolution of doors, windows, and configuration glass.

It can be seen from the questionnaire that Germany began to implement building energy-saving standards in 1971. After eight years of improvement until 1979, the glass used for doors and windows is still the coexistence of single-layer glass and double-layer glass. In terms of aluminum alloy profiles, the use of broken bridge aluminum alloy profiles accounts for only 10%, and most of them are still ordinary aluminum alloy profiles. After another 10 years, by 1989, insulating glass had been used for all glass, and ordinary aluminum alloy profiles had completely withdrawn from the market. It took 20 years from the 3.7W/m²K required for building energy efficiency to 2.8 W/m²K in 1989. With the improvement of energy-saving requirements, in just 6 years from 1989 to 1995, the German market's requirements for the K value of doors and windows increased to 2.0W/m²K, an increase of nearly 30%. From 1996 to 2000, the German door and window standard was raised again from 2.0W/m²K to 1.3W/m²K, a further increase of 35%. Until 2007, warm-edge insulating glass began to be used. After just five years, warm-edge insulating glass accounted for more than 50% of the market share in the door and window market. So far, in the German door and window market, the U value of the entire window is required to be between 1.2W/m²K and 1.3W/m²K. In terms of product configuration, the market share of warm-edge insulating glass has exceeded 63%, and the U value of multi-cavity PVC profiles, heat-insulating aluminum alloy profiles, and wood profiles has become an inevitable configuration.At present, China's door and window market is very similar to Germany's in 1989 in terms of the technical level of materials, design level, and market distribution situation. The development is similar. Taking the evolution of the German door and window market as a reference, we can conclude that the future Chinese door and window market will be dominated by triple-layer insulating glass, warm-edged inflatable insulating glass, and large series of high-energy-saving profiles. However, according to the current market situation, we need to pay attention to the following aspects:

(1) The material properties of the door and window profiles and the analysis of various elements in the design process of the frame profile structure will become the key factors for whether the frame profiles can meet high-quality applications;

(2) Warm-edge insulating glass will become the standard configuration of building doors and windows, but the current market situation in China requires a clear understanding of the performance of warm-edge materials and problems arising from improper use, otherwise, it will lead to the loss of warm-edge products confidence;

(3) If the insulating glass is not filled with air, it will not be able to meet the requirements of energy-saving indicators, but once the insulating glass is filled with air, then according to the current domestic material performance and processing quality, whether it can meet the high-quality requirements will be determined in the future Inside has become the main topic of industry doubts.

Due to the limited space, the following only talks about LIJIANG Glass's views on warm-edged insulating glass.

3. The warm edge insulating glass

The warm edge insulating glass is relative to the traditional metal spacer insulating glass. There is a clear definition in ISO standard IS010077 called thermal improvement spacer. The standard stipulates that X (dx9) <0.007, where d is the wall thickness of the spacer Dimensions, and Nine is the thermal conductivity of the spacer material. China's building materials industry standard JC/T2453-2018 was written by the author. In this standard, the definition of warm edge performance of warm edge insulating glass can not only be theoretically calculated according to ISO standards but also can be tested by testing warm edge insulating glass. The equivalent thermal conductivity of the edge of the insulating glass is obtained by testing. Theoretically, the equivalent thermal conductivity of the warm edge insulating glass should be between 0.15~0.9W/m²K. The formulation of industry standards provides clear guidance for the selection and determination of warm-edge insulating glass for customers inside and outside the industry and contributes to the development of the industry. However, there are also certain deficiencies. The biggest deficiency is the warm-edge insulating glass spacer. The material cannot be clearly defined and PVC materials cannot be used. Due to the current situation of domestic standard formulation, we can only refer to relevant foreign standards to determine the indicators of domestic standards under the condition of lack of experimental data support and actual cases as reference. However, under the provisions of discriminatory regulations in foreign countries, any written material cannot stipulate that a specific material cannot be used. Therefore, when writing the JC/T2453-2018 standard, we could not exclude PVC materials from the selection of standard materials, which caused a misunderstanding in the domestic industry that PVC materials can be used for insulating glass spacers, and also led to warm-edge insulating glass. There are a lot of problems with the application.

Why can't PVC material be used as spacer material for insulating glass? What harm will there be in using PVC material? PVC material is only a representative, the most important thing is not to use materials that produce volatiles under the action of light aging as spacer materials. Because the periphery of the insulating glass is sealed, the air inside the cavity is a stationary gas. When the sunlight enters the room through the insulating glass, it will be refracted by the glass and then enter the indoor side after being refracted by the air. If the molecular diameters of the air are the same, then The refractive index will be the same. However, if spacers with volatile substances are used on the edge, polymer gas will be volatilized under the sunlight. The molecular diameter of these gases is different from that of air, so the refractive index of light is also different, and light crossing will occur at the edge. put one's oar in. If white glass is used, people cannot distinguish it from the naked eye due to its better transmittance. When Low-E glass is used as the original insulating glass, especially when ultra-clear Low-E glass is used as the original insulating glass, the interference effect will be Zooming in will eventually lead to light interference chaotic patterns on the edges of doors and windows, which is academically called polarization effect, as shown in Figure 1. This effect will have a great impact on the appearance of doors and windows, and will also bring loss to the service life of doors and windows, so you must be careful when choosing the material of the warm edge spacer!

Figure 1 Polarization effect

What benefits can warm edge insulating glass bring to users?

(1) Warm-edge insulating glass can increase the indoor ambient temperature at the contact point between the insulating glass and the window frame, and reduce the possibility of condensation on the indoor surface of the window, thereby reducing the pollution of the interior decoration surface and the possibility of mildew on the wall, and improving the indoor environment. Under the standard conditions of -20°C outdoors and 20°C indoors, the edge temperature of the traditional aluminum spacer insulating glass is -4.5C, and under the same conditions, the traditional aluminum spacer is replaced with Technoform's warm edge TGI spacer, Then the surface temperature at the same position inside the hollow glass chamber reaches 0.6°C, which is 5°C higher. Under the premise of ensuring no condensation, the indoor relative humidity can be increased from 23.07% to U35.12% under the condition that the indoor temperature in the north is kept at 16°C in winter, and the indoor living comfort is greatly improved.

(2) Warm-edge insulating glass can reduce the temperature difference between the edge of the insulating glass and the center of the glass, reducing the possibility of glass self-explosion and thermal stress cracking during the application process of the glass. Too many construction projects in China have the phenomenon of self-explosion of tempered glass and thermal stress cracking of coating and insulating glass. Although these phenomena appear due to factors such as silver sulfide impurities and alumina impurities inside the glass body, the inducing factors in the application process lead to product failure. The reasons for the problems are rarely studied, which leads to various problems. To reduce the early failure of architectural insulating glass, the use of warm-edge insulating glass is one of the most economical solutions.

(3) Warm-edge insulating glass can reduce the U-value of the entire window by 0.2W/m²°Co At present, in the door and window industry, many people have misunderstandings, that is: as long as the U-value of the door and window profiles and the U-value of the insulating glass are well designed, the two can get the U value of the whole window according to the area-weighted calculation. These are two misunderstandings. Through the calculation formula of the U value of doors and windows, we can clearly understand that the linear heat transfer coefficient of the contact part between the door and window profiles and the glass also has a great influence on the U value of the entire window. According to the size of the window separation, The size and the U value of the profile are good or bad, and the linear heat transfer coefficient can affect the U value of the whole window, and the degree of influence is from 0.2W/m². To 0.8W/m²℃, which is a very important factor for the U value design of the whole window. How to choose warm edge insulating glass? Article 3.4.1 of JGJ102-"Technical Specifications for Glass Curtain Wall Engineering" clearly stipulates that when insulating glass is used for glass curtain walls, in addition to the relevant provisions of the current national standard "Insulating Glass" GB/T11944, the following requirements should also be met.

(1) The thickness of the insulating glass gas layer should not be less than 9mm.

(2) Insulating glass should be double-sealed. Butyl hot-melt sealant should be used for the first seal, and its performance should meet the requirements of the current industry standard "Butyl Hot-melt Sealant for Insulating Glass" JC/T914. The second sealant of insulating glass used for the hidden frame, semi-hidden frame glass curtain wall, and point-supported glass curtain wall should use silicone sealant, and its performance should meet the requirements of the current national standard "Silicon Structural Sealant for Insulating Glass" GB24266; The second sealant of insulating glass for frame curtain wall can be polysulfide sealant, polyurethane sealant or silicone sealant.

(1) The spacer frame of insulating glass can be made of a metal spacer frame or composite spacer frame of metal and polymer material, and the spacer frame can be folded continuously bending or gusseting, hot-melt spacer strips are not allowed. The desiccant in the interval frame should be filled with a fully automatic molecular sieve filling machine; therefore, the application range of hot-melt butyl warm-edge insulating glass products such as TPS adhesive strips is limited to residential buildings, and most public buildings are due to most If it is designed as a curtain wall, it is impossible to use warm-edge insulating glass legally. This result is similar to the current application in European and American markets. Although insulating glass made of the above products is occasionally used in some domestic curtain wall projects, this is adopted without the user's understanding. Once the domestic standard requirements are known, This kind of glass cannot be widely used in China.

When applying the warm edge spacer as an alternative to aluminum strips, the internal gas retention rate must be considered. According to the requirements of the Chinese national standard GB/T11944 and the European standard EN1279, the gas retention rate inside the insulating glass must be guaranteed every year. The leakage rate is less than 1%. If it cannot be guaranteed that the spacer is continuously bent by an automatic aluminum strip bending machine and the efficient filling of molecular sieves by an automatic desiccant filling machine, or that the corner welding is used to form a frame spacer such as SWISSPACER, the gas protection outside the corner cannot be guaranteed. If the continuity of the membrane is not guaranteed, the leakage of the air in the insulating glass will not be guaranteed to meet the standard requirements, and the performance of the insulating glass will be affected, and the performance will be greatly reduced.

^{For more information about LIJIANG Glass insulating glass processing equipment and insulating glass processing accessories, please click here to learn more.}