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Several technical issues to improve the energy-saving of insulating glass①

1. Brief introduction

Since the oil crisis in the 1970s, the application of building energy-saving products has become the mainstream of the international construction industry. Many developed countries have guided, encouraged, and regulated the construction and building materials market from product technology development, technical guidance, application promotion to legislation, and other aspects. The application of type building materials has broad space. In the United States, the use of insulating glass doors and windows accounts for 82% of all glass windows, and the German government has legislated since the late 1970s to stipulate that new buildings that do not use insulating glass will not be approved for construction.

Some developing countries have been paying attention to building energy efficiency since the 1980s, and successively promulgated the "Building Law", "Energy Law", "Building Energy Efficiency Planning", "Civil Building Energy Efficiency Design Standards" and other relevant laws and regulations, making the use of energy-saving hollow glass doors and windows products Entered a new period.

For the entire building, the area of doors and windows accounted for more than 20% of the building area, and glass accounted for more than 70%. From the perspective of energy conservation, about 50% of the energy loss of the entire building was on doors and windows. According to the experience of developed countries, the more developed the economy, the higher the standard of living, and the more civil energy consumption. With the economic development of developing countries, the current ratio will continue to expand. Therefore, reducing the energy consumption of building doors, windows, and exterior walls, and improving the heat insulation and airtightness of building doors, windows, and exterior walls are urgent problems we face, which provides a policy basis for the development, promotion, and application of insulating glass products.

2. The performance of insulating glass

In the recently revised insulating glass standard, insulating 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 periphery to form a dry gas space between the glass layers. Because the gas inside the hollow glass is dry, the hollow glass has the functions of sound insulation, heat insulation, anti-condensation, reducing cold radiation, and enhancing the safety of the glass.

2.1 The principle of heat insulation and sound insulation of insulating glass

As we all know, there are three ways of energy transfer: radiation transfer, convection transfer, and conduction transfer.

Radiation transfer is the transfer of energy in the form of radiation through rays, which include visible light, infrared and ultraviolet radiation, just like the transfer of solar rays. Reasonably configured hollow glass and reasonable thickness of the insulating glass spacer layer can minimize the transmission of energy through the form of radiation, thereby reducing energy loss.

Convection transfer is due to the temperature difference between the two sides of the glass, which causes the air to drop on the cold side and rise on the hot side, resulting in air convection and loss of energy. There are several reasons for this phenomenon:

The first is the poor sealing between the glass and the surrounding frame system, causing the gas inside and outside the window frame to be directly exchanged to produce convection, resulting in energy loss; 

The second is the unreasonable design of the internal spatial structure of the hollow glass, which causes the gas inside the hollow glass to produce convection due to the temperature difference, which drives energy exchange, resulting in energy loss; 

The third is the temperature difference between the inside and outside of the windows that constitute the entire system. As a result, the temperature difference between the inside and outside of the insulating glass is also large. 

With the help of cold radiation and heat conduction, the air first generates convection on both sides of the insulating glass and then passes through the insulating glass as a whole to form a loss of energy. Reasonable hollow glass design can reduce the convection of gas, thereby reducing the convective loss of energy.

Conduction transfer is through the movement of object molecules to drive energy to move, and achieve the purpose of transfer, just like using an iron pan for cooking and soldering things with an electric soldering iron, and hollow glass conducts energy transfer through the glass and its interior. The air is done. We know that the thermal conductivity of glass is 0.77W/m² k. The thermal conductivity of air is 0.028W/m² k. It can be seen that the thermal conductivity of glass is 27 times that of air, and the presence of active molecules such as water molecules in the air affects the energy transfer and convection transfer performance of hollow glass The main factor, thus improving the sealing performance of insulating glass, is an important factor in improving the thermal insulation performance of insulating glass.

2.2 Anti-condensation, reduction of cold radiation, and safety performance of insulating glass

Since there is a desiccant that can adsorb water molecules inside the hollow glass, the gas is dry, and when the temperature is lowered, condensation will not occur inside the hollow glass. At the same time, the dew point on the outer surface of the hollow glass will also increase. high. For example, when the outdoor wind speed is 5ms, the indoor temperature is 20°C, and the relative humidity is 60%, the 5mm glass starts to condense when the outdoor temperature is 8°C, while the 16mm (5+6+5) insulating glass under the same conditions, the outdoor temperature Condensation starts when the temperature is -2℃, and the 27mm (5+6+5+6+5) three-layer insulating glass starts to condense when the outdoor temperature is -11℃.

Due to the good insulation performance of insulating glass, the temperature difference between the two sides of the glass is large, and the effect of cold radiation can also be reduced; when the outdoor temperature is -10℃, the temperature in front of the indoor single-layer glass window is -2℃ and the hollow The temperature in front of the glass window is 13℃; in the same house structure when the outdoor temperature is -8℃ and the indoor temperature is 20℃, the cold radiation area of 3mm ordinary single-layer glass accounts for 67.4% of the indoor space, while the double-layer Insulating glass (3+6+3) is 13.4%.

The use of insulating glass can improve the safety performance of the glass. In the case of using the same thickness of the original glass, the wind pressure strength of the insulating glass is 1.5 times that of the ordinary single glass.

2.3 The structural composition of insulating glass

According to the place where the insulating glass is used and the purpose of use, the raw materials and structure of the insulating glass are also different. For example, in the southern region, where the temperature is higher throughout the year and the duration of light is longer when using insulating glass, more consideration is to control the external heat to enter the room less. When choosing the original insulating glass, it will be more important. Consider the use of coated glass in many places; in northern areas, the main purpose of using insulating glass is heating and heat preservation, so more consideration will be given to choosing transparent glass as the original sheet of insulating glass. Wherever noise needs to be controlled, three-layer or gas-filled insulating glass is needed to achieve the purpose of use.

With the development of the economy, the varieties of insulating glass products have also developed more, and the varieties of raw materials used have also increased. Such as hollow glass for curtain walls; hollow glass for automobiles and trains; hollow glass for electrical appliances; hollow glass for decoration (including hollow glass for inlays, hollow glass producing by automatic vertical insulating glass production line), and so on. All these products, although the raw materials used are different due to different uses, the basic composition is the same as below:

Glass-All flat glass and its deep-processed products are the basic components of insulating glass;

Figure 1 The flat glass

Figure 1 The flat glass

Sealant-Seal the edges and sides of the insulating glass to ensure that as little water vapor as possible enters the interior of the insulating glass, and prolong the failure time of the hollow glass;

Figure 2 The sealany sealing glue

Figure 2 The sealany sealing glue

Desiccant-ensure that all water vapor sealed in the hollow glass is absorbed cleanly, and the water vapor that enters the hollow glass over time is absorbed to ensure the life of the hollow glass;

Figure 3 The desiccant

Figure 3 The desiccant

Spacer Bar-control the distance between the inner and outer glass of the insulating glass, and control the external water vapor to be completely isolated in this part, to ensure that the insulating glass has a reasonable space layer thickness and service life.

Figure 4 The spacer bar

Figure 4 The spacer bar

From the above we can see: among all the raw materials that make up the insulating glass, the performance of the sealant and desiccant has a greater impact on the service life of the insulating glass product; when considering energy conservation issues, the gap between the spacer and the sealant.

The thermal conductivity will directly affect the side insulation performance of the insulating glass, thereby affecting the overall thermal insulation performance of the doors and windows. 

After decades of development, the production technology of insulating glass is constantly improving. The heat and sound insulation performance of the product has been improved from the earliest welding method, welding method to the cemented aluminum strip method. 

After the oil crisis in the 1970s, people found that the side insulation performance of aluminum strip method products was poor, and it must be improved to improve the overall insulation performance of the insulating glass. 

By the early 1980s, the world's first warm-edge system of insulating glass came out, this is Swiggle plastic strip system insulating glass. This kind of insulating glass has improved edge insulation performance because the sealing performance of the rubber strip has been improved, the service life is longer, the overall insulation effect of the insulating glass is better, and the market application of the insulating glass products has been broader.

In the next article, Several technical issues to improve the energy-saving of insulating glass②, the author will specifically introduce the composition of Swiggle rubber strips, the selection of insulating glass Swiggle rubber strips, and ways to improve the technical performance of insulating glass.

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

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