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What is low e glass?


Low-E glass, also known as Low emissivity glass, there is a film system consisting of multiple layers of metal or other compounds coated on the glass surface. The coating layer has the characteristics of high transmission of visible light and high reflection of middle and far-infrared rays, which makes it have excellent heat insulation and good light transmission compared with ordinary glass and traditional architectural coated glass.


Glass is an important building material, and its use in the construction industry is increasing as the requirements for building decorativeness continue to rise. However, when choosing glass windows and doors for buildings today, people are more concerned about their heat control, cooling costs, and comfortable balance of internal sunlight projection, in addition to their aesthetic and cosmetic features. This makes the newest member of the coated glass family, Low-E glass, stand out and become the focus of attention.


YS tells you about the performance of low e glass


Excellent thermal performance


Heat loss from exterior windows and doors is a major part of a building's energy consumption, accounting for more than 50% of a building's energy consumption. Relevant research data show that the heat transfer from the inner surface of the glass is dominated by radiation, accounting for 58%, which means that to reduce the heat loss from changing the performance of glass, the most effective way is to suppress the radiation from its inner surface. The emissivity of ordinary float glass is as high as 0.84, which can be reduced to less than 0.15 when coated with a silver-based low-emissivity film. Therefore, the use of Low-E glass for building doors and windows can greatly reduce the transfer of indoor heat energy to the outdoors caused by radiation, achieving the desired energy-saving effect.


Another significant benefit from the reduction of indoor heat loss is environmental protection. During the cold season, the emission of harmful gases such as CO2 and SO2 caused by the heating of buildings is an important source of pollution. If Low-E glass is used, the fuel consumed for heating can be significantly reduced due to the reduction of heat loss, thus reducing the emission of harmful gases.


The heat through the glass is bi-directional, i.e. heat can be transferred from indoor to outdoor and vice versa, and it is simultaneous, it is only a matter of the difference in heat transfer. In the winter, the indoor temperature is higher than the outdoor, requiring insulation. Low-E glass can achieve the requirements of winter and summer, both insulation and thermal insulation, and play an environmentally friendly low-carbon effect.


Good optical performance


The visible light transmission rate of Low-E glass ranges from a theoretical 0%-95% (difficult to achieve with 6mm white glass), and the visible light transmission rate represents the indoor lightness. Outdoor reflectivity from 10%-30% or so, outdoor reflectivity is the visible light reflectivity, representing the intensity of reflection or dazzling degree, at present, China requires that the visible light reflectivity of curtain walls is not greater than 30%.


Special cleaning brush for Low-E glass


Low-E glass has been widely used in developed countries due to the above-mentioned characteristics. low-E glass has high requirements for cleaning brushes in production because of the special characteristics of the material when it passes through the cleaning machine. Brush wire must be high-grade nylon brush wire such as PA1010, PA612, etc., wire diameter in 0.1-0.15mm is good. Because the brushed silk is soft, flexible, acid and alkali resistant, temperature resistant, can easily remove the dust on the glass surface, and will not cause scratches on the surface.


YS tells you about low e glass production


Two current methods of Low-E glass production


In-line pyrolytic deposition method.

These products are done during the float glass cooling process. Liquid metal or metal powder is sprayed directly onto the hot glass surface, and as the glass cools, the metal film layer becomes part of the glass. As a result, the film layer is hard and durable. The "Low-E" glass produced by this method has many advantages: it can be heat bent, tempered, does not have to be used in a hollow state, and can be stored for long periods of time. Its disadvantage is that it has poor thermal properties. Unless the film is very thick, its "u" value is only half that of sputtered "Low-E" coated glass. If you try to improve the thermal properties by increasing the film thickness, the transparency is very poor.


Off-line Vacuum Sputtering

The off-line method of producing Low-E glass is the most common vacuum magnetron sputtering coating technology used internationally. Unlike the high-temperature pyrolytic deposition method, the sputtering method is offline. There are horizontal and vertical glass transfer positions.


The sputtering process to produce "Low-E" glass, a layer of pure silver film as a functional film. The pure silver film between the two layers of the metal oxide film. The metal oxide film protects the pure silver film and acts as an intermediate layer between the layers to increase the color purity and light transmission.


In the vertical production process, the glass is placed vertically on a shelf and fed into a vacuum environment of the order of 10-1 Pa, and the appropriate amount of process gas (inert gas Ar or reactive gas O2, N2) is introduced and the vacuum level is kept stable. The target material Ag, Si, etc. is embedded in the cathode, and a magnetic field is placed in the horizontal direction perpendicular to the cathode to form a magnetron target. With the magnetron target as the cathode and a DC or AC power supply, the process gas is ionized and a plasma is formed under the action of high voltage.


Among them, electrons under the joint action of electric and magnetic fields, high-speed spiral movement, collision gas molecules, to produce more positive ions and electrons; positive ions under the action of the electric field, after reaching certain energy to hit the cathode target, the sputtered target is deposited on the glass substrate to form a thin film. In order to form a uniform and consistent film layer, the cathode target moves back and forth close to the glass surface. To obtain a multilayer film, multiple cathodes must be used, each moving back and forth across the glass surface to form a certain film thickness.


The horizontal method is to a large extent similar to the vertical method. The main difference is in the placement of the glass, which is transferred by a horizontally arranged wheel, through the cathodes, and the vacuum level changes after the glass pass through a series of pin set valves. When the glass reaches the main sputtering chamber, the coating pressure is reached, the metal cathode target is fixed and the glass moves. During the passage of the glass through the cathode, the film layer is formed.


At present, the target products of most magnetron sputtering coating lines are sunlight-controlled film glass with mainly monolithic and metallic films coated. The process of these products is relatively simple and the requirements for equipment are low. Therefore, these lines cannot meet the requirements of LOW-E glass coating.


The sputtering method of producing "Low-E" glass has the following characteristics.


The sputtering method can be used to produce Low-E glass in a variety of configurations due to the availability of a wide selection of metal targets and combinations of metal targets. Sputtering is also superior to thermal spraying in terms of color and purity, and because it is an offline method, it is more flexible in terms of new product development. The main advantage is that the "u" value of sputtered "Low-E" insulating glass is better than that of pyrolytic products, but the disadvantage is that the silver oxide layer is very fragile, so it is not possible to use it like ordinary glass. It must be made into hollow glass, and it is not suitable for long-distance transportation until it is made into hollow products.


YS tells you the features of low e glass


97% of the solar radiation energy is concentrated in the wavelength range of 0.3-2.5um, which comes from outdoor; the radiation energy of objects below 100℃ is concentrated in the long-wavelength band above 2.5um, which mainly comes from indoor.


If the room window is the boundary, winter or in high latitude areas we hope that the outdoor radiation energy in, and indoor radiation energy do not leak out. If the wavelength of radiation is the boundary, indoor and outdoor radiation energy is in the 2.5um wavelength of the dividing point. Therefore, the choice of room windows with certain functions becomes the key.


3mm thick ordinary transparent glass has a transmission rate of 87% of solar radiation energy, most of the radiant energy from the outdoors during the day; but at night or rainy weather, 89% of the thermal radiation energy from indoor objects is absorbed, so that the glass temperature rises, and then through the indoor and outdoor radiation and convective exchange of heat, so it can not effectively block the indoor heat leakage to the outdoors.


Low-E insulating glass has more than 60% transmission rate of solar radiation of 0.3-2.5um, and most of the radiant energy from outdoors can be transmitted during the day, but at night and in rainy weather, more than 50% of the heat radiation from indoor objects is reflected back into the room, and only less than 15% of the heat radiation is absorbed and then dissipated through re-radiation and convection exchange, so it can effectively prevent indoor heat from leaking outdoors. This characteristic of Low-E glass makes it have the role of controlling the one-way flow of heat energy to the outdoors.


Short waves of sunlight pass through the window glass and shine onto the objects in the room. After these items are heated, they are re-radiated as long waves. These long waves are blocked by the "Low-E" window glass and return to the room. The fact that re-radiation through the window glass is reduced to 85% greatly improves the thermal performance of the window glass.


The thermal insulation performance of window glass is generally expressed by the "u" value, which is directly related to the emissivity of the glass.


"u" value is defined as ASHRAE standard conditions, due to glass heat transfer and the temperature difference between indoor and outdoor, the formation of air to air heat transfer. Its imperial units are British thermal units per hour per square foot per Fahrenheit, metric units are: watts per square meter per Celsius, the lower the "u" value, the lower the heat transfer through the glass, the better the adiabatic properties of window glass. Radiance is the ratio of the heat radiated per unit area of an object to the heat radiated per unit area of a black body at the same temperature and under the same conditions. The definition of emissivity is the ability of an object to absorb or reflect heat. Theoretically, a perfectly black body absorbs 100% of all wavelengths. That is, the reflectance is zero. Therefore, the blackbody emissivity is 1.0.


Typically, float white glass has an emissivity of 0.84, while most in-line thermally polymerized "Low-E" coated glass has an emissivity between 0.35 and 0.5. The emissivity of magnetron vacuum sputtered "Low-E" coated glass is between 0.08 and 0.15. It is important to note that low emissivity directly corresponds to a low "u" value. The closer the emissivity of the glass is to zero, the better the thermal insulation performance.


The superiority of an "energy-efficient lighting system" must be reflected in the highest possible transmission of total solar energy while having the lowest "u" value. By considering both energy gain and heat loss, an energy balance equation is established, Ueg=UF-RFC. The lighting system with the best energy balance characteristics is vacuum magnetron sputtered "Low-E" coated insulating glass. Although the solar energy transmission of single-layer glass is the largest, its "u" value and "Reg" value are the worst. Therefore, it does not meet the need for a good energy balance.

A purely high solar energy transmission cannot be considered an energy-saving material if it does not effectively maintain this energy. Low-E" coated insulating glass is a better material for energy-efficient lighting. It has a high solar energy transmission, very low "u" value, and, due to the effect of the coating, "Low-E" glass reflects heat back into the room, making the temperature near the window glass is higher, and people do not feel much discomfort near the window glass. The indoor temperature of the building where "Low-E" glass is applied is relatively high, so the indoor temperature can be maintained relatively high in winter without frost so that people in the room will feel more comfortable. Low-E" glass blocks a small amount of ultraviolet light transmission, which is slightly helpful in preventing fading of interior items.


YS tells you the color of low e glass

In terms of process, low-E can be divided into the in-line deposition coating method and the off-line vacuum magnetic sputtering method. In terms of color, there are three basic shades of blue, green, and gray, and different processes can be made depending on the combination of different thicknesses and materials. For example, neutral colors, gold (rose gold), silver, and other relatively distinctive colors.


Low-E glass is currently divided into two types: online Low-E glass, offline Low-E glass.


Online Low-E glass varieties single.


Offline Low-E glass varieties, according to the characteristics of different climates can be made high, medium, and low a variety of transmittance products, and color silver gray, light gray, light blue and colorless transparent, etc., with tinted glass, can also be made green and many other colors. YS tells you what you need to pay attention to in the production process.


1. In-line Low-E glass will be subjected to high temperatures close to the softening point of the glass during the tempering process, at which time the color of the film may have some changes, resulting in color differences.


In addition, the tempering of online Low-E glass is tempered with film, the presence of the film makes the heating of both sides of the glass asymmetric, and the tempering process is difficult to control, which may produce a series of problems such as large tempering deformation.


While offline Low-E glass is tempered first and then coated, there is no problem. In order to avoid the above-mentioned tempering problems of online Low-E glass, some people use the untempered online Low-E glass as the inner piece of insulating glass, while the tempered clear glass is placed on the outside. This usage will not only have some effect on the effect of Low-E glass in the south but also may make the stress spot of the outer tempered white glass aggravated by the amplification of the inner Low-E glass. In contrast, the toughened offline Low-E glass on the outdoor side does not have this problem.


2. Low-E glass single piece off-line Low-E glass film surface is soft and will oxidize slowly when attacked by moisture and some oxidizing agents.


3. Online Low-E glass is "hard coated", and the shelf life of the film is 30 years. Off-line Low-E glass is "soft coating", the film layer is poorly solid and can hardly be kept naked.


4. Off-line Low-E glass must be processed into insulating glass in a very short period of time, and the side coating must be removed when forming insulating glass. Due to the weak respiration of insulating glass, water vapor, sulfide, oxide into the cavity will lead to the gradual loss of offline Low-E glass insulation performance, the appearance of darkening, discoloration, and the gradual appearance of a large number of mold spots.


Such as improper production will lead to low e glass quality is very poor. Therefore, you need to buy from regular manufacturers. Otherwise, the quality cannot be guaranteed, YS has specialized in glass production for over 30 years. low e glass is very simple for us.

According to market analysis, it is predicted that by 2015, the international market demand for Low-E glass will exceed 1 billion square meters, and in the next decade, the worldwide market demand for Low-E glass will grow at an average annual rate of more than 18%.



Single silver Low-E glass

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 five.

Double Silver Low-E Glass

Double silver Low-E coated glass has two functional layers (silver layers), plus other metal and compound layers, for a total of nine layers. However, the technical process control of double-silver Low-E glass is much more difficult than that of single-silver.


Comparison of single silver LOW-E glass and double silver LOW-E glass

Any coated glass will limit the transmission of visible light to varying degrees while limiting the transmission of solar thermal radiation. Double silver Low-E glass is able to block more thermal energy from solar heat radiation than single silver Low-E glass. In other words, with the same transmittance, double silver Low-E has a lower shading factor Sc, which filters sunlight into cooler sources to a greater extent.


Double silver Low-E glass has a lower heat transfer coefficient than single silver Low-E, which can further improve the thermal insulation performance of exterior windows and truly achieve warmth in winter and coolness in summer. Simply put, because double silver Low-E glass greatly reduces the heat exchange between indoor and outdoor environments through the glass, when the air conditioner is heating or cooling, the air conditioner can stay in standby mode long after the indoor temperature reaches the set temperature, thus saving power consumption.

YS tells you the advantages of double silver Low-E glass can be briefly summarized as follows.


1. Double silver Low-E glass has lower emissivity and lower heat transfer coefficient (U-value) than single silver LOW-E with the same glass combination.


2. Double silver Low-E glass has a lower shading coefficient, i.e., Sc value. 3.


3. With the same shading coefficient (Sc value), the visible light transmission rate is higher than that of a single silver Low-E. In short, double silver Low-E glass highlights the shading effect of the glass on solar thermal radiation, combines the high light transmittance of the glass with the low transmittance of solar thermal radiation skillfully, and successfully solves the problem of co-existence of the dual advantages of high light transmittance and low U-value and Sc-value, so it has a better energy-saving effect, which is an advantage that no other glass can have.




Is it better to have the coating on the #2 or #3 surface of an insulating glass unit? 


The light transmittance and U- value of the unit will be the same whether the coating is on the #2 or #3 surface, however, the SHGC will be lower when the coating is on the 2# surface.


In general, if you are concerned about reducing SHGC (typically in a cooling climate), then using the coating on the #2 surface would best meet the requirement. On the other hand, if you are interested in utilizing passive solar heat gain (typically in a heating climate) then using the coating on the #3 surface would best meet the requirement. 


Do all Low-E coated glasses look the same? 


No, they do not. Color differences between various Low-E coatings are due to the use of different coating materials, the thickness of the various coating layers, as well as differences in manufacturing processes. 


Will Low-E glass work only in northern climates? 


No, Low-E coated glass can work in all climates. 


LowE coatings reduce heat loss from the interior through windows, thus reducing the energy used to heat buildings and associated heating costs. 


And, LowE coatings also offer solar control that reduces heat gain due to both the transmitted solar energy and conducted heat caused by indoor and outdoor temperature differences. This reduces cooling loads and consequently the energy and costs associates with cooling the building.   


How can PPG Low-E work both in the summer and winter? 



In the winter, PPG Low-E glass keeps more heat inside by reducing the amount escaping through the glass and therefore reduces heating bills.

Some heat (long-wave infrared) is not permitted to enter the home, but this is outweighed by the benefits of the amount of extra heat kept inside (much fewer heat escapes). 


Some short wave infrared is still allowed to enter the home and is converted into heat. 



In the summer, PPG Low-E glass reduces the amount of heat that enters through the glass thus reducing the solar heat gain and decreasing cooling costs. 


How much does PPG Low-E glass reduce the transmission of ultraviolet (UV) energy? 


The reduction in the transmittance of UV energy is dependent on the specific PPG Low-E coating and the make-up of the insulating glass unit, i.e., glass thickness, glass type, etc. Please refer to the product performance charts elsewhere on the PPG Website for specific information.  


The Low E coated glass improves the insulating properties of the insulating glass unit, while the tinted glass reduces the influx of solar energy through the insulating unit.


How do I know that my window actually has Low-E glass? 


Low-e glass is a plain sheet of glass that has a coating put onto one of its two surfaces. To improve the insulating properties of windows, that plain sheet of glass is put together with another piece of glass to make a sealed insulating glass unit. The Low-E coating goes inside the insulating unit.  


You can test for the low-E coating in a window by doing the following:      


Hold a match or a penlight up in front of the window. You will see four reflections of the flame from the match or the light from the penlight when you look at the glass. 


If you have Low-E, one of the images will be a different color than the rest of the images. 
If your window has no Low-E, the four reflected images will be the same color. 


How does argon gas work?  


Insulating glass can be made with air between the lite of glass or it can be made with other gases between the lite of glass. Putting argon inside the insulating glass in a window improves the insulating value of the IG unit and the overall window. The bottom line is, less heat flows through a window with argon between the lite of glass than through a window with air between the lite.   


LOW-E glass, glass is an important building material, with the requirements of the building increasing decorative glass used in the construction industry volume continued to grow. Today, however, people in the choice of glass doors and windows of buildings, in addition, to considering the aesthetics and appearance features, more emphasis on the heat control, cooling costs, and comfortable balance within the Sunshine projection problems.


The coated glass according to the different characteristics of products can be divided into the following categories: heat-reflective glass, low emissivity glass (Low-E), conductive film glass. 


 Heat-reflective glass coating on the glass surface is usually one or more layers such as chromium, titanium or stainless steel and other metals or metal compounds formed film, the product was rich in color, appropriate for the visible light transmission rate, a higher infrared reflectivity, a higher UV absorption rate, therefore, also solar control glass, mainly for construction and glass curtain wall;  Low-E glass is coated on the glass surface by a multi-layer silver, copper or tin and other metals or metal compounds formed film series, the products have high visible light transmission rate, a high infrared reflectivity, with good insulation properties, mainly for construction and automotive, marine and other modes of transport, due to poor film strength, general are made of hollow glass use; 


Conductive film-coated glass is the glass surface such as conductive indium tin oxide film, the glass can be used for heating, defrosting, defogging, and as a liquid crystal display, etc.;

If you have more questions, please email YS, YS manufactures glass for more than 30 years, YS is your glass expert.YS will customize your glass and recommend and produce the most suitable glass for you. Click the red button on the top right to send an inquiry to YS!