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When constructing glass buildings, should Low-E glass be online or offline?

Low-E glass (Low Emissivity Glass), as a kind of coated glass, not only has high visible light transmittance but also has the characteristics of strong infrared blocking, which can play the dual functions of natural lighting and heat insulation and energy saving. It is more and more widely used in construction. Low-E glass is mainly divided into "offline" and "online" according to the manufacturing process. So what characteristics do different production methods bring to the application of the product? As a design institute, how can Party A judge its cost performance?

1. What is the difference between the two concepts?

On-line Low-E glass is a float glass production line that uses special equipment to form a layer of low-radiation functional film on the surface of the glass ribbon on the float glass production line through chemical vapor deposition and special materials. The Low-E glass produced by this process is called online Low-E glass. Its film material is semiconductor oxide, and the product color is only a few varieties such as cold gray, colorless and transparent.

Offline Low-E glass adopts special vacuum magnetron sputtering coating equipment and process technology to coat a multilayer composite film on the surface of the glass to realize the Low-E function. The main functional film layer in the film layer is generally silver (Ag) film layer, and other metal and compound film layers are auxiliary film layers, which can strengthen the adhesion between the film layers, adjust the reflection color of the film layer, and control the light transmittance and reflectance. , Protect the Low-E film from scratches and corrosion.

2. What is the difference in optical performance?

Optical performance is a major performance. It can be said that optical performance determines the performance and color of Low-E glass. For Low-E glass, whether it is online or offline, the absorption rate of radiant energy is generally very low, and the reflectance is generally only in the visible light band, which can be ignored in engineering.

Offline Low-E glass has a multi-layer structure, which can control the reflectance and reflection color of visible light and infrared wavelengths through the interference of light between the layers. The optical performance indicators cover a very wide range.

Online Low-E glass is generally a single film structure, and its color and reflectivity are mainly determined by the performance of the film itself, so the optical performance coverage is small.

3. What is the difference in energy-saving performance?

Energy saving is the main characteristic of Low-E glass, and it is also a technical indicator that users care about. Low-E glass is generally made into the hollow glass and used in buildings. The mainstream product structure is tempered Low-E hollow glass, which combines the two energy-saving forms of Low-E and hollows into one. It is a perfect combination and complements each other. The structure of laminated Low-E, laminated Low-E hollow, or tempered laminated Low-E hollow glass can also be used, which can provide better safety. In terms of energy saving, the shading coefficient Sc value of offline Low-E glass has a larger control range, which can be as low as 0.2 or less to more effectively block solar heat radiation, or as high as 0.7 or more to collect more sunlight. Thermal energy, which is very necessary to meet the energy-saving requirements of different climate regions. In addition, offline Low-E also has a lower heat transfer coefficient K value and better thermal insulation performance. 

In comparison, it is difficult to reduce the shading coefficient Sc value of online Low-E glass below 0.4. Under the same hollow glass structure, its heat transfer coefficient K value is also higher than offline Low-E, so the overall energy-saving effect is slightly worse. But the energy-saving effects of both are undoubtedly higher than that of non-Low-E glass products of the same structure by 40-50%.

4. What is the difference in machinability?

Online Low-E glass can be directly tempered, heat-increased, and hot-bent, and can be directly made into the insulating glass; while offline Low-E glass is generally made into insulating glass by first tempering white glass, and then coating. The early offline Low-E film cannot be thermally processed, otherwise, the film will be damaged and the Low-E function will be lost. The current coating technology has been able to mass-produce offline Low-E glass that can be tempered in different places, that is, first in the large plate. After coating the original piece of glass, it is transported to another place for tempering and synthetic hollow processing. At present, the products produced in this mode have become the mainstream products of Low-E insulating glass for building doors and windows. When synthesizing insulating glass with offline low-emissivity glass, it is necessary to remove the film on the edge of the glass to ensure the airtightness of the insulating glass and prolong the service life of the product.

5. What is the difference between variety and appearance?

There is a single variety of online Low-E glass. Due to the limitation of the large-scale production of float glass, generally only products with a thickness of 4-6mm are produced, and products with a thickness of 8mm and above are rarely produced due to market reasons. The color of the film layer is mostly gray and colorless and transparent. If other colors are needed, it needs to be coated on the colored glass. Considering the long period of the float glass production process to change the color, the flexibility of changing the color is poor. Offline Low-E glass is used to control the optical performance of the product by adjusting the material and thickness of each film layer. Therefore, the product variety is rich and diverse. Products with high, medium, and low light transmittance and reflectance can be made according to user needs. A variety of color series such as silver, gray, blue, green, brown, gold, and colorless and transparent are produced on colorless transparent glass, and more colors can be produced if matched with colored glass. The thickness can be produced from 3-19mm.

6. What is the difference in performance parameters?

The spectrum of online Low-E glass shows the characteristics of tin oxide conductive film, while the spectrum of offline Low-E glass shows the characteristics of silver and tin oxide composite film. Both have a good transmission for visible light, while the latter for near-infrared light. It has much higher reflection than the former, and the latter absorbs far-infrared radiation less than the former and has higher reflection. Therefore, online Low-E glass has a lower shading coefficient and heat transfer coefficient than offline Low-E glass.

The Low-E online glass 1

The Low-E online glass 1

The Low-E offline glass 1

The Low-E offline glass 1

7. What is the difference in electromagnetic shielding performance?

Low-E glass has the function of electromagnetic shielding, which can shield electromagnetic waves, prevent information leakage, and improve information security. The shielding effectiveness of offline single-layer Low-E glass is generally 19-28dB; while for online Low-E glass products, it is between 15-20dB.

8. What is the difference in product applicability?

In countries all over the world, online Low-E glass is mainly used in residential buildings, because residential buildings are usually short, the glass size is small, no toughening is required, and the price is cheap; while offline Low-E glass is mainly manufactured due to its wide variety of colors and excellent energy-saving effects. Cheng tempered insulating glass is used in high-end buildings such as public buildings and commercial buildings.

9. What is the difference in durability?

The online Low-E glass uses a tin dioxide semiconductor film, and its surface emissivity is 0.17-0.25. The tin dioxide semiconductor layer has very good chemical stability, so it can remain stable even in a bare environment. Change, whether it is used as a single piece or combined into the hollow glass, the film performance can be guaranteed to never attenuate. Traditional offline Low-E glass uses metallic silver as a functional film to block infrared radiation. The initial emissivity of the film layer is 0.05-0.15. However, if the silver layer comes into contact with trace amounts of sulfur and oxygen in the air, a chemical reaction will occur. The emissivity will be significantly increased, which will increase the heat transfer coefficient of the glass, and cause serious discoloration of the glass film. The current coating technology can make the protective layer very dense to improve the corrosion resistance and scratch-resistance of the Low-E film. Even so, offline Low-E glass cannot be used as a single layer. A new product recently launched on the market-offline silver-free Low-E glass, its functional layer blocking infrared radiation is a semiconductor compound, the film is corrosion-resistant and scratch-resistant, so the film surface can be exposed in the indoor natural environment as a single piece Use, or use it as a sandwich Low-E structure product.

10. How cost-effective is the glass?

In developed countries such as Europe and the United States, there are corresponding laws and regulations, so that users and manufacturers can only use Low-E glass and make it into an insulating glass structure to meet the energy-saving indicators specified in national laws and regulations. Chinese country's current "Design Standards for Energy Efficiency of Public Buildings" and "Design Standards for Energy Efficiency of Residential Buildings" also stipulate energy-saving indicators in different climate regions. From the value of indicators, only Low-E insulating glass can meet the design requirements. The state encourages users to use Low-E products to facilitate energy conservation and environmental protection, improve air quality, and improve the living environment.

Because offline Low-E glass is more energy-efficient than online Low-E glass, and architects pursue the unique style of architectural works, most of them choose offline Low-E glass products with a rich variety of colors and better energy-saving performance. Online products are more often used in residential buildings or ordinary low-end buildings. Under the premise of the same glass structure, the costs of the two products are roughly the same.

11. Concluding

Finally, Jinan LIJIANG Glass would like to remind you that whether offline Low-E glass or online Low-E glass is essentially coated glass, it has similarities to a certain extent. In actual applications, it should be selected according to architectural design requirements and construction costs. good. The current status quo is that the utilization rate of offline coated glass in large public construction projects is as high as 98%, while the utilization rate of the two in civil residential projects is equivalent. This is mainly determined by its performance and price. In the past, white glass was mostly used in civil residences. After all, the performance of online coated glass is better than that of white glass, and the price is relatively cheap, so it is more suitable for civil residential use. Public building projects pursue building grades, appearance and color effects, and higher energy-saving requirements, and use high-end offline coated glass products.

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