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Abstract: This article discusses the various factors that affect the energy saving of insulating glass, and then reveals the necessity of transitioning low-performance insulating glass to high-performance insulating glass; by comparing the influence of different sealing structures on the sealing life of the insulating glass, it is necessary to improve the sealing life of insulating glass The conclusion of using dual-channel sealing instead of single-channel sealing structure; introduces the basic status of the current insulating glass in developed countries, and introduces the super spacers that are increasingly used as a necessary configuration of high-performance insulating glass in foreign countries.

At present, the energy consumption of buildings in various countries in the world accounts for about 27.6% of the total energy consumption of each country, and the energy consumption of doors and windows accounts for about 25-30%. The basic energy-saving measure used to solve the energy consumption of doors and windows is to increase efforts to promote the use of insulating glass, and to reduce and eliminate the use of single-layer glass or double-glass windows as soon as possible. But the current situation is that, on the one hand, the use of insulating glass is very limited. According to statistics, the production of insulating glass in my country in 2003 was 30 million square meters, accounting for about 5% of the completed building area that year and 1% of the existing area. On the other hand, the energy-saving performance and quality of used insulating glass are uneven. In the limited use of insulating glass, medium and low performance insulating glass accounts for more than 90% (the concept of high and low performance insulating glass will be discussed below), and the sealing structure and materials that affect the sealing life of insulating glass are also used by many companies to adopt backward structures and Unqualified raw materials.

This article aims to 

(1) discuss the various factors that affect the energy saving of insulating glass, thereby revealing the necessity of transition from low-performance insulating glass to high-performance insulating glass; 

(2) by comparing the influence of different sealing structures on the sealing life of insulating glass The conclusion that the sealing life of insulating glass must use double sealing instead of single-sealing structure; 

(3) Introduce the basic status of insulating glass in developed countries, and introduce the super high-performance insulating glass that is becoming more and more widely used abroad as super spacer bars, which were a necessary configuration for high-performance insulating glass.

High-performance insulating glass

To understand the concept of high-performance insulating glass, one should first understand the several ways of heat transfer and the concept of insulating glass.

Insulating glass

According to the national standard GB 11944-2002, hollow glass is defined as a product in which two or more pieces of glass are evenly spaced for effective support and bonded and sealed around the edges to form a dry gas space between the glass layers.

The definition has the following meanings:

1) The insulating glass can be composed of two or more pieces of glass;

2) The structure of insulating glass is a sealed structure;

3) The gas in the insulating glass cavity must be dry;

4) The insulating glass must contain a desiccant.

However, the national standard for insulating glass focuses on the production and testing methods of insulating glass and does not define the energy saving of insulating glass. Therefore, to explore the energy saving of insulating glass, we must understand the relationship between insulating glass and several ways of heat transfer.

Three ways of heat transfer

The three ways of affecting the heat transfer of insulating glass are heat radiation, heat convection, and heat conduction. Among them, heat radiation accounts for 50-60% of heat transfer, and heat conduction and heat convection account for about 20-25%, respectively.

Ordinary insulating glass

The energy-saving of hollow glass mainly depends on its barrier method to heat transfer.

From the perspective of energy saving, the configuration of ordinary insulating glass includes transparent glass (commonly known as white glass), air, and trough aluminum spacers.

The white glass insulating glass 1

 The white glass insulating glass 1 

Insulating glass adopts a sealed structure, and the dry air in the glass spacer air layer is in a static state within 15mm, which solves the heat convection in the heat transfer. As a result, its U value is approximately 3 W/m² ·K, which is 50% better than the U value of 6 W/m² ·K for the heat transfer of a single glass.

However, the heat radiation and heat conduction of ordinary insulating glass for heat transfer has not been solved, as shown in Table 1. Therefore, energy-saving is very limited. By improving the arrangement of the hollow glass elements, the energy-saving effect of the hollow glass can be further improved.

 Insulating glass configuration elementsEmissivityThermal conductivity W/m·K
Transparent glass0.84
Aluminum spacer
160
Air
0.024
Glass
1

Table 1 Technical parameters of common insulating glass configuration elements

High-performance insulating glass  

From the perspective of energy saving, the high-performance insulating glass starts from three aspects of solving heat transfer at the same time. It adopts low-emissivity glass, inert gas, and warm edge spacer technology to further improve the energy-saving effect of insulating glass.

Insulating glass configuration elementsEmissivityThermal conductivity W/m·K
Low-E glass

Online Low-E0.1-0.2
Offline Low-E0.1
Argon Gas
0.016
Super spacer
0.168

Table 2 Technical parameters of high-performance insulating glass configuration elements

By using different materials to replace the materials of ordinary insulating glass configuration, the energy-saving effect of insulating glass can be continuously improved. Substituting Low-E glass for transparent glass in ordinary insulating glass can improve energy saving by 25%; on this basis, using warm-edge super spacers will further increase the energy-saving effect by 36%. The use of high-performance insulating glass configuration, namely low-emissivity glass, super spacers, and argon gas, reduces the heat transfer of the insulating glass at the same time from three aspects, and the U value is reduced to 1.6 W/m2·K. Compared with the ordinary insulating glass configuration, The energy-saving effect is improved by 44%, as shown in Table 3.

   

Insulating glass configurationCentral U value of insulating glass W/m² ·KEdge sealWhole window performance
W/m² ·K
Compared with ordinary hollow glass windows, the performance is improved by%
Replace transparent glass with Low-E glass
Air
Double glass hollow channel1.8Metal spacer2.125%
Low-E glass
Polysulfide

Use Low-E glass instead of transparent glass, warm-edge super spacers instead of aluminum spacers
Air
Double glass hollow channel1.8Super spacer1.936%
Low-E glass
Hot melt butyl rubber

High-performance insulating glass: Low-E glass, super spacers, and argon
Argon Gas
Double glass hollow channel1.6Super spacer1.644%
Low-E glass
Hot melt butyl rubber



Table 3 Energy-saving performance of high-performance hollow glass windows

The warm edge technology

Compared with the low-emissivity glass and the inert gas argon in the high-performance insulating glass configuration, our understanding of the warm edge technology currently widely used in developed countries is very superficial. However, the warm edge technology plays an important role in the configuration of high-performance insulating glass, so it is necessary to discuss this.

The main purpose of people using insulating glass is to save energy. However, in the structure of ordinary insulating glass, the thermal conductivity of aluminum spacers is 160 W/m·K, which is 6667 times that of air and 160 times that of glass (see Table 1). It is not difficult to see that when there is a temperature difference between indoor and outdoor, the heat energy runs away through the aluminum spacer (cold bridge), which becomes the weak rib of the hollow glass for energy saving. Therefore, aluminum spacers are also called cold edges.According to statistics from the American Door and Window Association, in 1990, insulating glass made with aluminum spacer technology (ie cold edge) accounted for 85% of the North American market, while insulating glass made with spacers with low thermal conductivity accounted for only 15%; but by the end of 2000 Cold edge technology has dropped to 20%, while the market share of spacers with low thermal conductivity has risen to 80%.

The warm edge technology 1

The warm edge technology 1

The definition of warm edge   

Any kind of spacer can be called a warm edge as long as its thermal conductivity is lower than that of aluminum. According to this definition, the warm edge can be obtained in three ways:   

(1) Non-metallic materials, such as super spacers, TPS, glass fiber strips;   

(2) Some metal materials, such as broken bridge spacers, real only high spacers;   

(3) Metal spacers with a lower conductivity than aluminum, such as stainless steel spacers.  

It can be seen that the definition of warm edge in developed countries is very loose. Therefore, we can divide it into the following three categories according to the energy-saving performance: low performance, medium performance, and high-performance spacers.

The high-performance spacers of insulating glass 1

The high-performance spacers of insulating glass 1

Table 4:

Low-performance spacerMedium performance spacerHigh-performance spacer
Shiweigao rubber strip (with aluminum tape inside)Shiweigao rubber strip (contains stainless steel belt)Super spacer
Thermal insulation spacer (aluminum thermal insulation spacer)PPG's U-shaped (stainless steel)spacerTPS
Stainless steel spacer
Fiber glass spacer
U-shaped spacer for PPG

and many moreand many moreand many more

(1) The feature of low-performance spacers is that they contain some metals or use metals with a lower thermal conductivity than aluminum. Using NFRC (National Door and Window Rating Committee) standard window, the U value of the whole window improved by low-performance spacers is 0.01, using SIGMA (American Sealing Insulating Glass Manufacturing Association) to test the U value of insulating glass, U value The degree of improvement is 0.01~0.02 (quoted from SIGMA Technical Report TR-140-96).   

(2) The feature of the medium performance spacer is that it contains some metal or uses metal with a lower thermal conductivity than aluminum metal. Using NFRC (National Door and Window Rating Committee) standard window, the U value of the whole window improved by low-performance spacers is 0.02, using SIGMA (American Sealing Insulating Glass Manufacturing Association) to test the U value of insulating glass, U value The degree of improvement is 0.03~0.04 (quoted from SIGMA Technical Report TR-140-96).  

(3) The high-performance spacer is characterized by the use of non-metallic materials, so the thermal conductivity is much lower than that of aluminum. Using NFRC (National Door and Window Rating Committee) standard windows, the U value of the whole window improved by low-performance spacers is 0.03, using SIGMA (American Sealed Insulating Glass Manufacturing Association) to test the U value of insulating glass, U value The degree of improvement is 0.04~0.05 (quoted from SIGMA Technical Report TR-140-96).

In conclusion

In summary, ordinary insulating glass only basically solves the heat convection in heat transfer but does not solve the heat radiation and heat conduction, so energy saving is very limited. If you want to further improve the energy-saving effect, it is necessary to use Low-E glass, argon, and high-performance warm-edge spacers.

Insulating glass has a history of more than 100 years from its birth to the present, and it has developed into today’s high-performance insulating glass. Although the popularization of insulating glass in some developing countries has only been more than 10 years, developing countries don't need to wait until 100 years before adopting it. High-performance insulating glass configuration should be taken in a philosophical approach. This is not only technically feasible but also urgently needed to further improve building energy efficiency.

In addition, if the configuration of insulating glass directly affects the energy-saving effect of insulating glass, the use of insulating glass sealing materials and reasonable structure directly affects the sealing life of the insulating glass, thereby affecting whether the insulating glass can exert energy-saving effects for a long time.


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