What is Low-E Glass? Application in the Construction Industry
- What is Low-E glass?
- How does Low-E Glass Works?
- Manufacturing Process and Classification of Low-E Glass
- What are the Low-E glass Manufacturing Processes?
- What are the Classifications of Low-E Glass?
- Application of Low-E Glass in Building Energy Saving
- Contribution of Low-E Glass to Energy Saving
- Features of Low-E Glass
With the rapid development of science and technology, glass has gradually entered the high-tech industry from traditional industries, and its application has extended from buildings to solar panels and LCD TV panels. In recent years, it has been widely used in touch products such as tablet computers and mobile phones, and even in the automotive industry. The design of green buildings emphasizes the improvement of energy efficiency and environmental tolerance to achieve the purpose of environmental symbiosis and co-prosperity. Therefore, the use of building materials in green buildings must be adjusted according to the different climates in different places. One Low-E Energy Efficient Glass is the world's highest performance in-line coated low-E glass.
What is Low-E glass?
Low-E glass (Low Emissivity) is a film product composed of multiple layers of metal or other compounds coated on the surface of the glass. The coating layer has the characteristics of high transmission of visible light and high reflection of middle and far-infrared rays. In simple terms, this glass transmits light, but when thermal energy (infrared) from the sun or HVAC hits the Low-E glass, it is reflected into the original space instead of being passed through the glass.
How does Low-E Glass Works?
Low-E glass usually looks tinted but is not the same as tinted glass. Colored glass is made by adding alloy materials to the glass itself, while the surface of Low-E glass has a microscopic thin layer (usually multiple layers) composed of various metal particles. These thin layers of metal turn the Low-E glass into a filter, allowing it to filter light and in turn have excellent thermal insulation properties.
Different types of energy have different wavelengths. By adding thin layers of various metals to the glass surface, you can choose which type of energy to filter. If you want to filter out heat (long wavelengths, i.e., infrared) while allowing light (shorter wavelengths) to be taken directly.
Manufacturing Process and Classification of Low-E Glass:
At present, there are two mature process technologies for commercial manufacturing of Low-E glass, namely, vacuum magnetron sputtering process (offline Low-E) by physical method and chemical vapor deposition process (online Low-E) by chemical method.
What are the Low-E glass Manufacturing Processes?
- Vacuum magnetron sputtering process:
Vacuum magnetron sputtering technology refers to a technology that uses the magnetic field matched on the cathode surface to form electron traps so that the electrons drift close to the cathode surface under the action of E×B. The principle is to make the material to be deposited into a target (cathode), connect the target to high pressure, put transparent glass without visible impurities into a vacuum chamber filled with inert gas, and place it at a certain distance from the cathode and positive. on the anode on the target surface. The inert gas is usually Ar, and a high voltage is applied between the cathode and the anode, and a glow discharge is generated between the two stages to generate plasma. Under the action of the electric field, the electrons collide with argon atoms when they fly to the glass substrate, and the collision ionizes new electrons.
As the number of collisions increases, under the action of the electromagnetic field, new electrons gradually move away from the target surface, fly to the glass substrate, and deposit on it. The ionized argon ions are accelerated to the target, and bombard the target surface with high energy, resulting in sputtering, in which the target atoms or molecules are also deposited on the glass substrate to form a thin film, which is the phenomenon of physical vapor deposition. The coated glass must meet certain aesthetics while pursuing energy saving. Therefore, the target needs to move back and forth on the surface of the glass substrate, so that the coated film can be uniform and have a certain thickness. This method is called offline vacuum magnetron. Sputtering is a novel new technology for material synthesis and processing.
Because the vacuum magnetron sputtering process and equipment are used to coat the Low-E film on the glass plate, there is a molecular bond between the film layer and the surface of the glass plate, and the firmness between the film layer and the glass surface is low, and the film layer itself is relatively soft, easy to be scratched and worn, the silver film is easy to be oxidized and denatured when exposed to the air for a long time, so the offline Low-E glass film is also called soft film. Due to the characteristics of its soft film, offline Low-E glass cannot be used bare, that is, cannot be used alone. Low-E glass is usually made into insulating glass, and the Low-E film is in the air cavity of the insulating glass to protect the Low-E film from scratches and abrasions. And a dry inert gas (Ar) should be filled between the two pieces of glass, which can not only protect the Low-E film layer from being oxidized but also reduce the U value of the heat transfer coefficient of the insulating glass and increase the heat insulation of the insulating glass.
- Chemical vapor deposition process:
Chemical vapor deposition is a chemical technology, which mainly uses one or several gas-phase compounds or elemental substances containing thin-film elements to perform chemical reactions on the surface of the substrate to form thin films.
- Forms volatile substances.
- Transfer the above material to the deposition area.
- A chemical reaction occurs on a solid and produces a solid substance.
What are the Classifications of Low-E Glass?
- By functional layers:
- Single silver Low-E coated glass usually contains only one functional layer (silver layer), plus other metal and compound layers, the total number of film layers reaches 5 layers.
- Double silver Low-E coated glass has two functional layers (silver layer), plus other metal and compound layers, the total number of film layers reaches 9 layers. However, the technical process control of double silver Low-E glass is much more difficult than that of single silver.
- Three silver Low-E coated glass has three functional layers (silver layer), plus other metal and compound layers, the total number of film layers reaches more than 13 layers.
- By transmittance:
- High transmittance type: the light transmittance is more than 70%, which can allow a large amount of visible light to enter the room. The low-E glass used for winter warmth in northern China is generally high-transparency Low-E glass, which can not only keep warm but also meet the needs of natural lighting.
- Medium transmission type: The light transmittance is 50%-70%, which has a strong blocking effect on visible light.
- Low transmittance type: the transmittance is below 50%, which has a strong blocking effect on visible light. Low-transmittance Low-E glass is suitable for places with strong sunlight. While meeting the normal lighting needs, the light will not be too dazzling.
- By shading coefficient (Sc):
The shading coefficient refers to the coefficient of the ability of glass to block sunlight. The higher the value of the shading coefficient Sc, the more solar radiation enters the room through the glass, which is suitable for the northern regions with long winters. The lower the value of shading coefficient Sc, the better the blocking effect of direct solar radiation, which can reduce the direct solar radiation entering the room, which is suitable for the southern region with long summer.
- By heat transfer coefficient (U):
The U value of the heat transfer coefficient indicates that in a steady-state, the inner and outer surfaces of the glass take one square meter of heat within a unit time and temperature difference. Under the same indoor and outdoor temperature difference, a low U value means that the glass transmits less heat energy due to heat transfer due to the temperature difference, and the glass has good thermal insulation performance, which is suitable for areas with high indoor thermal insulation requirements in winter.
Application of Low-E Glass in Building Energy Saving:
- High latitude and cold regions
In North America and Northeast China, these regions have long winters, extremely low temperatures in winter, short daylight hours, and weak light intensity. High-transmittance Low-E glass can maximize the use of natural light due to its better light transmittance. At the same time, a coating surface is placed on the inner layer of the Low-E glass to achieve a better thermal insulation effect.
Application principle: The indoor temperature is higher than the outdoor, the far-infrared heat radiation mainly comes from the indoors, and the Low-E glass can reflect it indoors to keep the indoor heat from leaking. For part of the solar radiation from the outdoors, Low-E glass can still allow it to enter the room. This part of the energy is absorbed by the indoor objects and then converted into far-infrared heat radiation and left indoors.
- Areas with hot summer and warm winter
In Southeast Asia, most of the regions are hot in summer and warm in winter. The temperature rises rapidly in summer, and the demand for heating in winter is lower than that in northern regions. Single-silver or double-silver Low-E glass can be used in these areas, so it is difficult for outside heat to enter the room, reducing the energy consumption of air conditioning cooling.
Application principle: The outdoor temperature is higher than the indoor temperature, and the far-infrared heat radiation mainly comes from the outdoors. Low-E glass can reflect the mid-and far-infrared rays in the sunlight, and only allow the visible light to be taken, so that the sunlight becomes a cold light source and prevents the heat from entering the room. This not only achieves the purpose of energy-saving but also meets the needs of indoor lighting.
- Areas with hot summer and cold winter
Nevada, USA, Central China. The climatic characteristics of this region are that the four seasons are distinguished, the temperature difference between winter and summer is large, and the climatic conditions are relatively complex and more changeable. In these areas, low-transmittance and shading-type Low-E glass can be used, which can reduce the light transmittance of the glass in summer, prevent the outdoor heat radiation from entering the room, and make the heating inside the building less obvious. In winter, although the low transmittance of Low-E glass is relatively low, it can meet the normal lighting needs, and at the same time, it can prevent indoor heating and other heat from being transmitted outdoors.
In this type of area, it is necessary to consider the heat dissipation in summer, and at the same time pay attention to keeping warm in winter. With proper Low-E glass, a balance can be found between summer and winter, to maximize the energy-saving effect and achieve a win-win situation for lighting needs.
Contribution of Low-E Glass to Energy Saving:
- The Low-E film can reduce the heat transfer caused by the temperature difference on both sides of the glass (i.e., temperature difference heat transfer).
- The Low-E film can effectively block solar radiation, thereby limiting the radiant heat energy (i.e., radiation heat transfer) of the sun shining through the glass.
Features of Low-E Glass:
- The elegant and beautiful blue-gray appearance meets the requirements of aesthetic design.
- Good low radiation and solar control performance, with low reflected light, low shading coefficient, and low U value.
- The low-radiation performance helps the building block outdoor high temperatures in summer, reducing air-conditioning electricity bills.
- Low-E properties help buildings maintain the indoor temperature in winter, reduce heating loads, and save energy and low carbon.
- The highly durable in-line coating ensures that the product is easy to handle and process over long distances.
- It can be cut, glued, strengthened, bent, and glazed as easily as ordinary glass.
- There is no need to remove the edge when synthesizing the hollow, which reduces labor costs and improves efficiency.
- It can be stored in a single piece for a long time, and the supply and patch can be guaranteed at any time.
- It can be installed and used in a single piece, and the film surface will not be oxidized and discolored.
- The color is stable before and after the online film layer processing, and the color of each glass is the same.
- Available in a variety of sizes and thicknesses.