Table of Contents
What are insulated glass units?
Insulated glass units are a glass product composed of two or more flat glass panes separated by spacers and sealed with airtight sealant to create a dry airspace between the glass. It is an ideal eco-friendly and energy-saving material that meets the requirements of modern architectural glass. It has the advantages of thermal insulation, sound insulation, heat insulation, light regulation, and can also prevent window condensation in winter, thus saving energy.
What are the types of insulated glass units?
There are various types of insulated glass with different properties based on their functionality, the number of glass panes used, and the type of spacer. They can generally be categorized into the following:
Based on functionality: regular insulated glass, functional composite insulated glass, and point-supported multi-functional composite insulated glass.
Based on the number of glass panes used: double-pane insulated glass, triple-pane insulated glass, and multi-pane insulated glass.
Based on the type of spacer used: metal spacer bar insulated glass and composite adhesive spacer insulated glass.
Based on the production method: fusion insulated glass, welding insulated glass, and adhesive insulated glass. Currently, in the world of insulated glass production, adhesive insulated glass accounts for 55% to 60%, welding insulated glass accounts for 30% to 35%, and fusion insulated glass accounts for approximately 10%.
What are the excellent characteristics of insulated glass units?
Insulated glass, which is made by separating two or more flat glass panels with gas-tight sealing material, has many excellent characteristics compared to single-pane glass, including:
Excellent energy-saving performance: Modern buildings consume energy mainly for air conditioning and lighting, with air conditioning accounting for 55% and lighting 23% of the total consumption. Glass is the thinnest and most heat-conductive material in the exterior wall of buildings. The desiccant in the aluminum frame of the insulated glass keeps the air inside the glass dry for a long time, making it extremely energy-efficient.
High sound insulation: Insulated glass can reduce noise by 27 to 40 decibels. For example, outside traffic noise of 80 decibels will only be 50 decibels indoors.
Frost elimination: Single-pane glass can frost up due to the large temperature difference between indoor and outdoor. However, the inner glass of the insulated glass is affected by the air layer, so even if the outer layer comes into contact with low temperature, it will not condense on the glass surface due to temperature difference. The dew point of the insulated glass can reach 1702 (excluding composite rubber strip insulated glass).
Improved wind pressure resistance: The wind pressure resistance of insulated glass is 15 times that of single-pane glass, which is the main indicator for curtain walls to withstand wind load.
Glass is less prone to self-explosion: The production method of insulated glass is bonding and cold processing, and the stress in the original glass sheet does not change. The glass is sealed with elastic material around it, which makes it less prone to self-explosion.
Coated glass film layer does not peel off: The metal film surface of coated glass cannot be exposed to the air for a long time, but the metal film surface of the insulated glass is in a dry sealed air and will never peel off.
What is the thermal insulation principle of insulated glass units? How is the insulation effect represented?
When buildings use single-layer windows, sunlight in the summer can create a greenhouse effect. This means that some of the sunlight that hits the glass is reflected, but some enters the room and increases the temperature. In the winter, single-layer windows play a role in heat dissipation because of the high heat transfer coefficient of glass. Insulated glass can reduce both conductive and convective heat transfer and radiation heat transfer.
Energy is transferred through three forms: radiation, convection, and conduction. Radiation transfer is energy transmitted through radiation, including visible light, infrared, and ultraviolet rays. There are generally two ways to reduce radiation transfer: first, to determine the spacing layer thickness reasonably; second, to use sunlight control glass, such as low-emissivity glass. Convection transfer occurs because there is a temperature difference between the two sides of the glass, causing air to descend on the cold side and rise on the hot side, creating air convection and causing energy loss. For insulated glass, since the intermediate gas is enclosed in a narrow space, i.e., when the spacing layer thickness of insulated glass is less than 12mm, the intermediate gas will not generate convection. Conduction transfer is achieved through the motion of object molecules, which drives energy to move and achieves the transfer purpose. For insulated glass, this is accomplished through glass and intermediate gas. Since the thermal transfer coefficient of air is 0.028W/(m2·K), which is 1/27 of glass, and air does not convect, the conductive transfer of air is almost negligible. The edges of the two pieces of glass are sealed off by sealant, and the main conductive material of insulated glass, glass, is restricted. According to measurements, in the comprehensive energy transfer of insulated glass, radiation transfer accounts for 60%, conductive transfer accounts for 37%, and convective transfer accounts for 3%.
The thermal insulation effect of insulated glass can be represented by the light transmittance of the glass and the heat transfer coefficient K value [W/(m2·C) or W/m2·K] of the glass window.
The definition of the K value is the amount of heat transmitted from one side of the glass component to the other side of the air per unit time under standard conditions. The smaller the K value, the better the insulation performance: the larger the K value, the worse the insulation performance.
What is the sound insulation principle of insulated glass units?
The sound insulation principle of insulated glass is as follows: the air inside the sealed space of the insulated glass becomes a dry gas with a low sound transmission coefficient due to the action of the desiccant in the rubber strip, thus forming a sound insulation barrier. If insulated glass is made of two sheets of glass with different thicknesses, the refraction index of sound waves is different when propagating in different media, causing refraction at the critical interface of the two media when passing through the insulated glass. As a result, most of the sound is reflected back, and resonance is avoided, making the sound insulation effect more significant.
Glass with the same thickness but different properties has little difference in reducing noise decibels. However, glass with different thicknesses but the same properties has different sound insulation performance. The thicker the glass, the better the sound insulation effect. However, the sound insulation effect of a single sheet of glass or two sheets of laminated glass with different thicknesses is not as good as that of insulated glass made from it.
From the perspective of noise control, the larger the air layer of insulated glass, the better the noise control effect. If the thickness of the air layer is less than 6mm, its sound insulation is only slightly higher than that of single glass of the same thickness. Generally, the air layer thickness of insulated glass is commonly used in two specifications: 9mm and 12mm; in special cases, it can be widened to 20-100mm.
How does the soundproofing effect of double-glazed windows compare to that of ordinary glass?
The loudness of sound is measured in decibels (dB), and people typically perceive environments around 30dB to be relatively quiet, while outdoor noise is usually above 60dB. When the sound changes by 5dB or more, people can perceive a significant difference. According to data, using a single-pane glass can reduce noise by 20-22dB, while using double-glazed windows can reduce it by 29-30dB. To improve the soundproofing effect of double-glazed windows, methods such as using asymmetrical flat glass with different thicknesses, filling the gap with special gases like sulfur hexafluoride, using PVB film to dampen sound waves, or using laminated glass are commonly used. With these methods, the soundproofing effect of double-glazed windows can reach 45dB.
What is the principle behind the anti-condensation of double-glazed windows?
During the winter, when using single-pane glass, condensation often forms on the inner surface of the glass, which is known as condensation. Condensation on window glass not only obscures the view but also contaminates the window frame, curtains, and walls, causing inconvenience in people’s daily lives. Double-glazed windows have excellent anti-condensation performance due to the presence of a desiccant that can adsorb water molecules inside the double-glazed unit. The gas inside the double-glazed unit is dry, so it will not produce condensation inside the unit even when the temperature drops, which raises the dew point of the outer surface. For example, when the outdoor wind speed is 5m/s, the indoor temperature is 20°C, and the relative humidity is 60%, a 5mm glass begins to condense when the outdoor temperature is 8°C, while a 16mm (5mm clear glass + 6mm air gap + 5mm clear glass) double-glazed window only condenses when the outdoor temperature drops to 12°C. A 27mm (5mm clear glass + 6mm air gap + 5mm clear glass + 6mm air gap + 5mm clear glass) triple-glazed window begins to condense at an outdoor temperature of 11°C under the same conditions.
What materials are typically used in the production of insulated glass units?
Insulated glass is typically composed of glass, sealing adhesive, spacer frames or bars, desiccant, and insulating gas, as detailed below:
(1) Glass: Glass is the main material used in insulated glass. It can be float glass, coated glass (such as heat-reflective or low-emissivity glass), heat-absorbing glass (in various colors), or safety glass (such as tempered or laminated glass). Functional glasses, such as self-cleaning glass, are also being developed for use in insulated glass.
(2) Sealing adhesive: There are two types of sealing adhesive used in insulated glass: the first and second sealing adhesives. The first sealing adhesive is typically made of butyl hot-melt adhesive, which has a low diffusion rate for water vapor and greatly extends the lifespan of insulated glass. The second sealing adhesive is most commonly made of polysulfide, which is used to structurally bond the glass pane to the spacer frame.
(3) Spacer frames/bars: Spacer frames or bars are used to separate the glass panes in insulated glass. Depending on the material used, they can be categorized as metal (aluminum), hybrid (stainless steel frame with sealant, aluminum frame with thermal break and wave-shaped aluminum bar as internal support), or thermoplastic spacer bars (super spacer and TPS). Traditional metal (aluminum) spacer frames are known as cold-edge spacer frames due to their good thermal conductivity. However, this leads to heat loss from the edge of the insulated glass through the metal, creating a “cold edge.” This “cold edge” energy loss is 2.2 times greater than that of the central portion of the glass. By contrast, a warm-edge spacer frame such as Swiggle improves the energy-saving effect of the insulated glass by raising the temperature of the glass edge by around 5 degrees Celsius, and reducing the temperature difference between the edge and center of the glass, which can reduce the possibility of spontaneous glass breakage.
(4) Desiccant: When using metal (aluminum) spacer frames to make insulated glass, desiccant is added to the cavity of the frame to keep the insulating gas inside the glass pane dry. Molecular sieve is the most commonly used desiccant.
(5) Insulating gas: The initial insulating gas used in insulated glass was dry air, but as demand for insulated glass increased, inert gases including argon, nitrogen, and sulfur hexafluoride were introduced as filling materials for the insulating space. Oxygen and fluorine primarily improve the insulating properties of the insulated glass, while sulfur hexafluoride primarily improves the sound insulation properties.
What performance should be possessed by the sealing adhesive used for insulating glass units?
The sealing adhesive used for insulating glass should have good resistance to water vapor permeation, gas leakage prevention, UV resistance, and adhesion to substrates. This is because, of the five performance indicators in GB/T 11944-2002, four indicators “sealing performance, initial dew point, high temperature and humidity, climate cycle” are used to test the sealing performance of insulating glass in various environments, while UV irradiation is used to test whether the sealing adhesive contains organic volatile substances that affect the line of sight. Therefore, the quality of the sealing adhesive for insulating glass will directly affect the performance of the insulating glass.
How to choose the sealing adhesive for insulating glass units?
Specifically, the following factors should be considered:
Compatibility between the sealing adhesive and glass;
Modulus of the sealing adhesive;
Ease of processing;
Water vapor permeability;
Adhesion strength to glass and spacer;
Inherent strength;
UV resistance;
Ability to maintain inert gas;
Compatibility with coated glass;
Harmlessness of the adhesive shrinking process to the environment and users.
What is a desiccant?
A desiccant is a type of drying agent that removes moisture from the atmosphere. It works by physically adsorbing water molecules into its own structure or chemically absorbing water molecules and changing their chemical structure to become another substance.
Why is a desiccant used in insulated glass units?
There are three main reasons why a desiccant is used in insulated glass:
To remove any moisture that is sealed inside the insulated glass during production.
To continuously absorb any moisture that may enter the air space between the glass panes during the lifespan of the insulated glass, in order to maintain a low dew point (less than -40°C). Moisture can enter the air space due to improper aluminum frame corner treatment, inadequate sealing adhesive application, and changes in temperature causing glass deflection and increased moisture permeation through the sealing adhesive.
To remove any volatile organic compounds (VOCs) that may be sealed inside the air space during production, as well as any VOCs that may enter the air space during the lifespan of the insulated glass.
What types of desiccants are typically used in insulated glass units?
The desiccants typically used in insulated glass are molecular sieve and silica gel (i.e. silicon dioxide).
What are the characteristics and technical specifications of hollow glass desiccant?
Hollow glass desiccant should comply with national environmental protection requirements, and have strong water absorption capacity, stable moisture absorption rate, low dew point, selectable particle size, good fluidity, and other characteristics. The technical specifications for hollow glass desiccant are as follows:
Particle size (spherical): 1~4mm ≥ 90%
Color: off-white, brown, or light red.
Bulk density: 0.65~0.85g/mL.
Static water adsorption ≥22%.
Compressive strength: 10~30N/particle.
Wear rate ≤0.2%.
Packaging moisture content: ≤5%.
Water absorption rate ≤0.6mg/(g•min).
Static nitrogen adsorption ≤2.0mg/g.
How to choose a desiccant?
The selection of a desiccant depends on its adsorption performance, and the most important factor to consider is its absorption capacity for water, air, and solvents. The desiccant’s absorption capacity for water, air, and solvents depends on the temperature and the required dew point.
The desiccant’s absorption capacity for water and solvents changes with temperature and dew point. The higher the temperature of the desiccant, the lower its absorption capacity for water. The lower the dew point, the lower the desiccant’s absorption capacity for water. Silica gel does not actually absorb water at low dew points and can only absorb a significant amount of water at very high dew points, which can lead to fog formation. 13X desiccant has the highest water absorption capacity, 4A desiccant is second, 3A desiccant is third, and silica gel has the lowest.
The absorption and release of gases by hollow glass desiccants are crucial because they directly affect the curvature of the glass. 13X desiccant has the highest moisture and solvent content but also has the highest air adsorption, which increases the risk of hollow glass cracking, making it the worst option. When solvent adsorption is not required, 3A desiccant has all the ideal properties. However, if solvent adsorption is needed, no single desiccant has all the ideal properties. An optimal desiccant is a mixture of materials that have high water adsorption, sufficient solvent adsorption, and low air adsorption. Mixing 3A and 13X desiccants (or 3A and silica gel) can achieve these properties.
What should be noted when using desiccants?
When using drying agents, the following issues should generally be noted:
① Drying agents are susceptible to moisture absorption and may become ineffective, so it is essential to store them in a sealed container.
② The recycling bin for drying agents must be sealed.
③ If the opened drying agent container is not completely used, it should be sealed and not left open to the air.
④ The recycled molecular sieve must be dehydrated by drying it in a 300°C oven for 3 hours before use.
What is the function of the spacer material in insulating glass units? What are the materials for spacer?
The function of the spacer material for insulating glass is as follows:
① Maintaining the appropriate distance between the two glass panes.
② Ensuring the strength of the insulating glass by providing support for the glass and sealant.
③ Providing adhesion for the first and second sealants.
④ Providing sufficient space for filling desiccant.
⑤ Enabling printing or engraving of the production date and product identification of the insulating glass.
The spacer material for insulating glass can be classified according to the material used into three types: aluminum spacer, stainless steel spacer, and composite spacer made of organic material and stainless steel.
What is an aluminum spacer frame?
An aluminum spacer frame is made of aluminum alloy, with common types including 6A, 9A, 12A, 15A, 16A, and 20A. It has good verticality and anti-warping properties.
What is a stainless steel spacer frame?
A stainless steel spacer frame is made of stainless steel, with common types including 6A, 9A, 12A, 15A, 16A, and 20A.
What is an organic material and stainless steel composite spacer frame?
An organic material and stainless steel composite spacer frame is made of stainless steel and polypropylene, with common types including 8A, 12A, 15A, 16A, and 20A.
What are the gases used for filling in insulated glass units?
The most commonly used gases for filling in insulated glass are dry air, oxygen, argon, and sulfur hexafluoride (SF6). Inert gases such as chlorine and krypton have the characteristic of large molecular volume/weight, move slowly in the air, and can reduce the gas molecule movement due to temperature difference in the air layer, thus reducing heat loss caused by convective heat transfer. Therefore, insulated glass filled with inert gas has outstanding performance.
What are the characteristics of insulated glass units filled with inert gas?
Insulated glass filled with inert gas has the following characteristics:
After filling, it can reduce the pressure difference between the inside and outside, maintain pressure balance, and reduce glass cracking caused by pressure difference.
After filling with chlorine, it can effectively improve the K value of insulated glass, reduce condensation on the indoor glass, and improve comfort level. That is, insulated glass filled with gas is less likely to condense or frost.
Due to the characteristics of inert gas, it can slow down the thermal convection inside the insulated glass, and also significantly improve its sound insulation effect, which can make the insulation and sound insulation effect of insulated glass better.
It can increase the strength of large-area insulated glass and prevent the middle part from collapsing.
It can increase the wind pressure resistance strength.
Since dry inert gas is filled, the air with moisture inside the insulated glass cavity can be replaced to keep the environment inside the cavity dry and prolong the service life of the molecular sieve inside the aluminum spacer.
When using low-emissivity LOW-E glass or coated glass, inert gas can protect the film layer and reduce the oxidation rate, prolonging the service life of coated glass.
What is a composite sealant strip?
A composite sealant strip is a type of composite sealing material developed by American chemists in the 1980s. It is mainly made of butyl rubber and embedded with corrugated support belts, which are then extruded into a certain shape and contain a desiccant inside. It is used in the production of insulating glass, for the internal partition support and edge sealing.
The biggest advantage of composite sealant strips is their simple operation, minimal material waste, low personnel requirements, low management costs, and good working environment. The disadvantage is that specialized equipment, such as a hot press machine, is required for the strips to absorb moisture.
What types of composite sealant strips are there?
According to their structure and shape, composite sealant strips used for insulating glass can be divided into rectangular strips and concave strips.
What is warm edge technology for insulating glass units?
The term “warm edge” refers to any spacer that has a lower thermal conductivity than aluminum. According to this definition, warm edge technology can be achieved through three methods: using non-metal materials with low thermal conductivity, such as super spacers, TPS, and glass fiber spacers; using partially metallic materials, such as thermal break spacers and high-density spacers; or using metallic spacers with thermal conductivity lower than that of aluminum, such as stainless steel spacers.
Therefore, the definition of warm edge is quite broad.
How does the humidity in the production environment affect the lifespan of insulating glass units?
Firstly, the humidity in the production environment directly affects the effective and residual adsorption capacity of the desiccant. The desiccant absorbs moisture from the spacer to meet the required initial dew point. Additionally, the desiccant also has adsorption capacity, which is referred to as residual adsorption capacity. The residual adsorption capacity determines the amount of moisture absorbed into the spacer through diffusion during the use of insulating glass, as well as the rate of moisture accumulation in the spacer. Therefore, it determines the effective usage time of the insulating glass. If the humidity is high during the production of insulating glass, the moisture sealed in the spacer will consume more adsorption capacity of the desiccant, resulting in less residual adsorption capacity.
Secondly, the humidity in the environment has a significant impact on the adsorption rate of the desiccant. The higher the humidity, the faster the adsorption rate of the desiccant. During the production process, the desiccant is exposed to the air for a certain period, and the adsorption capacity consumed by the desiccant is positively correlated with the environmental humidity. As a result, the residual adsorption capacity of the desiccant decreases as the humidity increases. Therefore, the humidity in the production environment has a crucial impact on the effective usage time of the insulating glass. To extend the effective usage time of insulating glass, it is necessary to control the humidity in the production environment at a lower level.
What is the impact of sealant on the service life of insulating glass units?
Choosing insulating glass sealants with low gas permeation coefficients is one of the effective measures to reduce gas diffusion rate. The commonly used sealants in the production of insulating glass include butyl rubber, polysulfide rubber, and silicone rubber, with gas permeation coefficients of 1-5g/(m2•d•cm), 7-8g/(m2•d•cm), and 10-15g/(m2•d•cm), respectively. It can be seen that butyl rubber has the smallest gas permeation coefficient.
What is the impact of adhesive layer thickness on the service life of insulated glass units?
The amount of gas diffusion through the polymer is inversely proportional to the thickness of the adhesive layer. The thicker the layer, the smaller the diffusion amount. Therefore, when using a double-sealed adhesive, the thickness of the outer layer should be 5-7mm, and when using a single-sealed adhesive, the thickness should be 8-12mm. During production, it is important to ensure the uniformity of the adhesive layer thickness, especially the tightness of the corner sealing.
What is the impact of reasonable design and material selection on the service life of insulating glass units?
When designing, it is necessary to fully consider the phenomenon of “thermal explosion” of glass and prevent large temperature differences from occurring on the surface or cross-section of the same piece of glass. To avoid “thermal explosion”, heat-absorbing glass that has undergone strong processing or coated glass with high transmittance can be selected based on the weather conditions of the place of use.
What is the impact of desiccant on the service life of insulating glass units?
For insulating glass produced manually or semi-manually, the desiccant injection process is not sealed, and the desiccant is exposed to the air, which will quickly absorb moisture from the air. If the desiccant’s adsorption rate is low, the amount of desiccant adsorbed will be small in the same amount of time, and the effective adsorption capacity lost will also be small. Similarly, shortening the process time is also to reduce the loss of adsorption capacity.
How to improve the technical performance of insulated glass units?
The technical performance of insulated glass can be improved by adjusting the thickness of the gas interlayer, the type and humidity of the gas in the air layer, strengthening the edge sealing, the thermal transmittance of the glass, and the plane size of the glass.
(1) Thickness of the gas interlayer: By controlling the thickness of the gas interlayer, turbulent airflow can be formed inside the insulated glass to control convective heat transfer and minimize the disturbance between cold and hot gas.
(2) Type and humidity of the gas in the air layer: The type of inert gas filled inside the insulated glass can reduce its thermal insulation and sound insulation properties. Filling the gas with argon or sulfur hexafluoride can respectively improve the thermal insulation and sound insulation performance of the insulated glass.
(3) Strengthening edge sealing: If the edge sealing of insulated glass is poor, the proportion of water vapor entering the inside of the insulated glass through the sealing layer will increase, which will reduce the lifespan of the insulated glass. On the other hand, if the thermal conductivity of the edge material is good, the thermal insulation coefficient of the insulated glass will increase, and the thermal insulation performance will decrease.
(4) Thermal transmittance of the glass: The heat transfer of insulated glass mainly occurs through radiative heat transfer. If high-transparency, low-reflectivity ordinary transparent glass is used, the thermal insulation performance of the insulated glass is much lower than that of high-reflectivity, low-transmission coated or LOW-E glass.
(5) Plane size of the glass: Enlarging the plane size of insulated glass can reduce the heat loss per unit area and improve the overall thermal insulation effect of the insulated glass. During the installation of insulated glass doors and windows, if the glass retaining strip is not installed properly or not sealed tightly, it can cause air circulation and energy loss, which will affect the performance of insulated glass.
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