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One article to know how to choose the best insulating glass for doors and windows

It can be said that when you buy doors and windows, if you can choose the insulating glass, the task has been completed.

Because 80% to 90% of the area of a door and window is composed of glass, glass almost determines the quality (service life, etc.) and performance (glass configuration) of door and window products.

Among them, insulating glass is the first choice for most users' doors and windows.

Figure 1 The insulating glass 1

Figure 1 The insulating glass 1 

In this article, Jinan LIJIANG Glass will show you how to choose the better insulating glass through several chapters.

1. What is insulating glass

A piece of compliant insulating glass (conventional) is composed of original glass, aluminum spacer, molecular sieve, first sealant (butyl glue), and second sealant (polysulfide or silicone glue).

The glass deep processing factory will first cut two pieces of glass of the same size according to the size required by the customer (it can be tempered or not). Excess water vapor, two sealants act as bonding and sealing materials.

Thus, a safe and energy-saving insulating glass is formed.

Figure 2 The internal structure of a complete piece of insulating glass

Figure 2 The internal structure of a complete piece of insulating glass

2. Why insulating glass has become the standard for doors and windows

The invention of insulating glass is to solve the problem of poor energy-saving and thermal insulation effect of building door and window glass (single-layer glass).

It can replace single-layer glass for three main reasons: first, light weight, the added weight of glass as a hollow layer is small; second, the cost is low, air is free, and the cost of auxiliary materials such as spacer sealant is relatively small. It is used to increase the thickness of the glass, or other methods (such as vacuuming) to improve the performance of the glass, and the cost performance is particularly high;

Figure 3 The insulating glass windows and doors

Figure 3 The insulating glass windows and doors

The third is the most important, the effect of energy saving and heat preservation is outstanding:

A good conductor of glass heat, the thermal conductivity is 0.90 W / (m K), and the thermal resistance is small;Air is a poor conductor of heat, the thermal conductivity is 0.024 W / (m K), and the thermal resistance is large;The heat transfer coefficient (K value) of glass with a thickness of 5 mm is about 5.8 W / (m² K);The heat transfer coefficient of 5 mm + 12 A + 5 mm insulating glass is about 2.7 W / (m² K);The heat transfer coefficient K value is one of the main parameters to measure the energy-saving performance of glass, which reflects the temperature difference heat transfer performance of the glass. The lower the K value, the better the performance;

The heat transfer coefficient of 6 mm + 12 A + 6 mm insulating glass is about 2.70 W / (m² K), and the heat transfer coefficient of 10 mm + 12 A + 10 mm is about 2.65 W / (m² K) );The K value of insulating glass with different glass thicknesses is almost the same. It can be seen that the energy saving of glass is not determined by the increase of glass thickness, but the K value of the hollow layer is greatly reduced;

Glass, coupled with broken bridge aluminum, plastic steel, solid wood and other door and window frames with energy-saving thermal insulation properties, doors and windows can finally be responsible for more than "perfect" (ventilation and lighting) in the building.

3. What are the most important usage requirements for insulating glass

Jinan LIJIANG Glass believes that the key core for consumers to choose insulating glass is the effective service life of insulating glass.

The effective service life of insulating glass refers to:

A reliable insulating glass should have an effective service life (continuous performance) of 15 years (or even more). During this period, the energy-saving and thermal insulation performance of insulating glass is stable (the K value can always maintain a level of more than two points).

What will happen to the effective service life of insulating glass:

If water vapor appears on the inner surface of the insulating glass (that is, the hollow layer) (that is, the ambient temperature reaches the dew point), it means that the performance of the insulating glass has failed (the service life has expired).

The reason is that the relative humidity of the air in the hollow layer is about 0.5 %RH (the relative humidity in our daily life is about 45 %RH ~ 75 %RH), and the dew point is very low (the dew point refers to The dew condensation temperature of insulating glass is the criterion for judging whether the insulating glass fails, and the dew point of normal insulating glass can reach minus 40 ℃).

When the relative humidity of the air in the hollow layer increases, the dew point of the insulating glass will also increase (the dew point of the failed insulating glass may be only three or five degrees or even ten degrees).

When the relative humidity of the air in the hollow layer becomes high, or the dew point is reached to condense water vapor, it means that the air thermal resistance of the inner surface is very low (the heat transfer coefficient of dry air is 0.021 kcal/(㎡·h·℃), and the water transfer coefficient is 0.021 kcal/(㎡·h·℃). The thermal coefficient is 0.5 kcal/(㎡·h·℃)), and the insulating glass almost loses the energy-saving and thermal insulation performance.

At the same time, it also shows that the sealant of the insulating glass has failed (broken or aged, so that it cannot block water vapor from entering the hollow layer), or the molecular sieve has failed (the molecular sieve is saturated with water vapor and cannot absorb excess water vapor). Low air humidity or condensation for a long time will also cause mildew, alkali precipitation, white spot, spacer corrosion, and even glass burst on the inner surface of insulating glass.

Figure 3 The Condensation on the inner surface of insulating glass 1

Figure 3 The Condensation on the inner surface of insulating glass 1

The current situation of insulating glass in the home improvement market:

The home improvement retail market is flooded with a large number of non-compliant and non-standard insulating glass products. The effective service life of these products is often only two to three years, three to five years.

Figure 4 The insulating glass aluminum spacer bar is corrosion

Figure 4 The insulating glass aluminum spacer bar is corrosion 

4. Selection, around the supply chain and glass processing

What I said in the last chapter is actually the true meaning of purchasing reliable insulating glass.

Glass selects qualified supply chains (raw materials), and glass deep-processing plants need production regulations. As long as these two conditions are met, it is difficult to think of glass quality.

Common problems and strategies of original glass:

In preparation, glass is used as the main material, and consumers only need to understand that in most cases, large factories such as North and South Glass can only be considered as the original glass manufacturers/brands, and the production of finished glass for home decoration is basically bought from downstream glass processing factories. 

Figure 5 Comparison of the original glass sheet and the finished glass

Figure 5 Comparison of the original glass sheet and the finished glass

Compared with the original glass manufacturers, they are all large and powerful manufacturers, and the original glass cannot be counterfeited. Most of the original glass of the finished glass is not bad.

It is the top priority for consumers to understand other supply chain options and workmanship of glass deep-processing manufacturers.

Common problems and strategies for two sealants:

In the preparation, two sealants for insulating glass are indispensable, and they complement each other (one has better air-tight effect, and the other has better water-tight effect), and together the two single pieces of glass are tightly connected together and form a relative Sealed, dry space.

Figure 6 the two sealants for insulating glass

Figure 6 the two sealants for insulating glass

But in reality, non-standard and non-compliant workshop-type processing factory may have uneven coating of butyl rubber (manual + rough), gaps or too narrow, and may also use double-sided tape (double-sided tape). Instead of butyl glue to fix the aluminum spacers, and it is even possible to directly omit the link of applying butyl glue.

Figure 7 The insulating glass butyl rubber coating is uneven

Figure 7 The insulating glass butyl rubber coating is uneven

Due to the large amount of the second sealant (polysulfide glue or silicone glue), the merchant may use inferior glue or oil-filled glue to reduce the cost (a lot of impurities, the smell may be irritating, the glue is very hard or very soft, which affects the performance of the glue and life), the dosage may be too small (manual + rough), or even not applied (yes, the real case, because the composite spacer is used, it is said that there is no need to apply secondary glue, the composite spacer does not have the function of secondary glue) .

Figure 8 Some tips to be aware of insulating glass butyl rubber coating

Figure 8 Some tips to be aware of insulating glass butyl rubber coating 

When purchasing, we could ask the merchant about the processing process of the first and second layers of glue, "Are the first and second layers of glue in your supporting glass factory completed by automatic machinery and equipment? Is the glass laminated by machine? Is the butyl rubber evenly coated by those automatic machinery and equipment? ", ask the material of the glue, you can express your concerns about the inferior glue "I heard that some people do not use butyl glue? I heard that many merchants use inferior glue?", you can also understand the brand of glue "used Does the glue have a brand? Is there a photo of the raw material brand?"

Jinan LIJIANG Glass thinks that machine gluing is a very common thing these days, and choosing a factory for machine gluing can directly avoid encountering small workshops with no strength (Note ①: If there is no small workshop, you must be embarrassed; Note ② : Except for special cases, such as extra-small and extra-large glass, it still needs to be glued manually;).

Video 1 The whole insulating glass lamination production line

The merchants understand the glass processing process very well, know the materials used in the supporting factories, or they can show you the video materials and take you to the construction site to watch, then you can rest assured.

Figure 9 The insulating glass Two-sealant sealing automatic sealing machine

Figure 9 The insulating glass Two-sealant sealing automatic sealing machine

Frequently asked questions and strategies for molecular sieves and spacers:

In the preparation, the role of molecular sieve and spacer as a partner is also irreplaceable. The spacer is the "skeleton" of the hollow layer of the insulating glass, which plays the role of evenly supporting and separating the glass. It is also the "storage bag" of the molecular sieve, which can store small particle molecular sieves without affecting the molecular sieve's function of absorbing water vapor.

Why do you need molecular sieves: The first and second sealants of insulating glass play a vital role in sealing and isolating air and water vapor, but the "glue" cannot directly reduce the air humidity in the hollow layer (review the previous article, Production The relative air humidity of the environment is several tens of percent, and the relative air humidity inside the insulating glass is only a few tenths of a percent).

Moreover, in the long-term use of insulating glass, the "glue" does not play a 100% "absolute seal", and the air-driven water vapor still has a certain penetration force.

Therefore, a "desiccant" is needed, that is, after the insulating glass is made, the molecular sieve quickly absorbs the water vapor in the air in the hollow layer, so that the relative humidity of the air in the hollow layer is rapidly reduced to about 0.5 %RH, and the molecular sieve lasts for more than ten years in the insulating glass, even During normal use for a longer period of time, it absorbs a small amount of water vapor in the air that the sealant "puts" in, delaying the time for the dew point of the glass to increase and avoiding the failure of the insulating glass. )

Figure 10 The insulating glass molecular sieve desiccant

Figure 10 The insulating glass molecular sieve desiccant

But in reality, non-standard and non-compliant workshop-type processing plants may use low prices, use calcium oxide, calcium chloride, clay desiccants, or use desiccants with a pore size of 4 A / 5A (there will be Low service life / poor water vapor absorption / corrosion of spacers and sealants, etc.).

It is also possible that the molecular sieve is less filled (for example, about 90 % of the spacers need to be filled, but only 50 % of the spacers / gusseted spacers are filled with only one and two sides of the four sides in order to save trouble), and it is not filled in time (just like puffed food, molecular sieve As soon as the package is unpacked, it begins to get wet, and it needs to be used on the same day as it is opened, not until it is used up), and even do not fill it (in a real case, fans have shaken the insulating glass at home and found that there is no sound, similar to an hourglass).

The spacer is also relatively recessive, the factory may use too inferior aluminum spacer (for example, the size error is large, making the finished glass uneven / burrs rough, which is not conducive to sealant sealing / the gap is not too small or too large, It is not conducive to the contact of molecular sieve with air or the leakage of molecular sieve).

Figure 11 The insulating glass bending aluminum spacer bar

Figure 11 The insulating glass bending aluminum spacer bar

When purchasing, we can ask the processing process of the spacers and molecular sieves of the merchants, "Are the spacers and molecular sieves of your supporting glass factory bent and filled by machine?", ask the material of the molecular sieves, so as to propose our own opinion on the inferior molecular sieves. Worry about "I heard that many molecular sieves are not 3A? What is 3A molecular sieve?", and also understand the brands of the two "Are they all brand-name products? Are there any photos of the raw material brands?"

Figure 11 The insulating glass 3A molecular sieve

Figure 11 The insulating glass 3A molecular sieve

In addition, if the merchant tells you that it is better to bend aluminum spacers, there is a certain reason, because the factory has a fully automatic spacer bending machine, indicating that the factory is more formal, but it is not necessary to buy bending, because if the factory works well, two In addition to the difference in appearance, performance can be said to have no effect.

Figure 12 The insulating glass machine bending and desiccant filling

Figure 12 The insulating glass machine bending and desiccant filling 

If the merchant tells you that black spacers are better (black aluminum spacers are more popular now), then you have to ask "what is the material?" If it is aluminum, the answer is that there is no difference except for the appearance. If it is some Warm-edged material, that's exactly what it is.

Figure 13 The composite material of insulating glass spacer bar

Figure 13 The composite material of insulating glass spacer bar

If the merchant recommends you to use composite spacers, Jinan LIJIANG Glass’s personal suggestion is to investigate more. The composite spacers are for the glass deep processing factory to reduce 3 processes: aluminum spacer bending (or gusset), spacer molecular sieve filling, spacer It is used for coating butyl glue to improve production efficiency and appearance of special-shaped glass.

It's essence is still aluminum spacers, but some businesses will use composite spacers to pretend to be warm edge strips. In addition, the quality of the composite spacer is uneven (some factories do not even apply a second sealant). If the deep processing manufacturer feels unreliable, it is recommended that consumers choose the traditional aluminum spacer process.

5. The performance improvement of insulating glass

Insulating glass is the basic type of door and window glass. In addition to choosing the quality of its products, you can also learn about the ways to improve its performance.
Plan No. 1 can achieve 5% - 10% improvement in energy-saving and thermal insulation performance without spending money: that is, the thickness of the hollow layer, from the perspective of energy-saving effect, the hollow layer should be between 9 A - 15 A (20 A and other large hollow layers) Glass layers are not suitable.

Of course, considering that the total thickness of the hollow laminated glass is relatively large (the notch limit for installing the glass on doors and windows), and the possible large glass situation (the hollow layer of the large glass should be larger to prevent the glass from absorbing), when consumers choose, You can consult the door and window business in advance for the appropriate glass configuration.

Door and window manufacturers have a complete set of glass pressing lines, and the product series is relatively large (the ratio of single window and single window, and the ratio of integrated window screen and integrated window screen, which cannot be confused), and the flexibility of glass selection and configuration is higher.

Figure 14 The iterative calculation of heat transfer coefficient of insulating glass

Figure 14 The iterative calculation of heat transfer coefficient of insulating glass

The second plan is to improve the energy-saving and thermal insulation performance of insulating glass by 5% - 10%: that is, the hollow layer is filled with inert gas, or aluminum spacers are added with warm edges.

The commonly used inert gas is generally argon gas (it can also be filled with krypton gas and xenon gas, which is less), and the price is 30 to 50 per square meter. Compared with ordinary air, it has 3 main characteristics:

  • First, the thermal conductivity is lower, so it is also often used for energy-saving and thermal insulation;
  • Second, the gas is inactive, which can protect and delay the oxidation time of silver ions in offline Low-E, thereby improving the service life of offline Low-E glass;
  • The third is to improve the safety of the large glass. The overall density of the inert gas is higher than that of the air, to protect the large glass from being squeezed by external forces (thermal expansion and contraction, strong wind, etc.) and reduce the hidden danger of internal interest.

The performance comparison of inert gases with different gas fillings

Gas typeThe content in air/%Density/Thermal Conductivity/Heat transfer coefficient/
(6mm white glass+12mm+6mm white glass) insulating glass
Air1001.290.02412.667
Argon gas0.931.780.01632.508
Krypton gas1.14*102.860.00872.454
Xenon gas0.09*104.560.00522.420

illustrate
  1. The content in air refers to the volume percentage
  2. Density and thermal conductivity refer to the situation at a temperature of 0 degrees Celsius and an atmospheric pressure of 101.325Kpa
  3. The heat transfer coefficient value is calculated by computer measurement software under the assumption that the 12mm intermediate layer is filled with 100% gas content.

When consumers buy insulating glass, they generally do not consider adding inert gas to improve the performance by 10% (considering the cost-effectiveness factor, adding Low-E Glass is also the same price), or making larger glass (5 ㎡ or so of the glass can be taken into account) when the incidental advantage performance.

Either when there is a need for energy saving and thermal insulation in the home (especially in the high latitudes of the northern hemisphere), when Low-E insulating glass has been used (to effectively extend the life of Low-E Glass), or the glass itself has a high configuration. (for the ultimate performance), it is more reasonable to increase the configuration.

Of course, the inert gas may also have the problem that the initial concentration is not high (the effect becomes worse, the service life becomes lower), and the escape is too fast (the sealant mentioned above cannot be completely sealed). Therefore, when choosing, you can also check a lot: "How about the fully automatic insulating glass gas-filled lamination equipment in the glass processing factory?" "What is the initial concentration of inert gas?" "What is the annual emission rate of the insulating glass you produce?" "High-concentration inert gas How many years can the gas be used effectively?" "Does the insulating glass you produce have a warranty? What should I do if it leaks?"

It should be pointed out that the Low-E glass that brings about a 33% improvement in heat transfer coefficient is an offline single silver coating with e=0.1. If the heat transfer coefficient is further improved, there are several options, which are to use double silver-coated Low-E glass, e=0.05, or to use argon gas. Its U value changes see the table.

The comparison of U-value improvement with Low-E coated glass and argon gas

Insulating glass configurationGlass central U valueGlass center △UImprovement △U brought by argon filling
E=0.1, Air1.82--
E=0.05, Air1.700.12-
E=0.1, Argon gas1.53-0.29
E=0.05, Argon gas1.360.170.34

The two heat transfer methods given in the table are the comparison between the ΔU brought by the Low-E coated glass and the argon gas. The basic configuration in the table is warm edge insulating glass, 3mm+12A+3mm Low-E coated glass; what is tested is the U value of the central COG of the wooden window. It can be seen from the data in the table that on the basis of using the single silver coating of Low-E glass, if double silver coating is used, e1(0.05)<e2(0.1), the U value will be improved to △U1=0.12, about 6.6% ; In contrast, the improvement brought by inflation is △U2=0.29, about 16%.

A cost-effective solution to improve thermal insulation performance;

Common warm edge spacers are mainly divided into rigid warm edge strips (such as ordinary stainless steel spacers, the inner core of German Technowind is PP material, and the outer TGI spacer is covered with stainless steel material, and the reinforced glass fiber of Saint-Gobain, France. SWISSPACER spacers), flexible warm edge strips (such as TPS spacer and 4SG spacers made of special butyl rubber made by German Comelin company, and SuperSpacer spacer strips with porous silicone foam and resin adhered by Conex company in the United States).

Figure 15 The composite material of insulating glass warm edge spacer

Figure 15 The composite material of insulating glass warm edge spacer

Their prices range from tens to hundreds of dollars. Compared with ordinary aluminum spacers, they have 2 main features:

First, the thermal conductivity of the warm-edge spacers is lower (the thermal conductivity of aluminum is 160 W/m·k, and the thermal conductivity of stainless steel with the highest thermal conductivity in the warm-edge is 15 W/m·k, many of which are at a few tenths), which improves the thermal conductivity of the glass. Energy-saving and heat preservation effect, which improves the problem of easy condensation on the edge of the glass;The second is the flexible warm edge spacer. Because it does not contain metal inserts, the overall sealing effect of the glass can be better (the metal spacer is due to seams, thermal expansion, contraction, etc.), which can improve the effective service life of the insulating glass and effectively solve the problem of inertia. The problem of gas escape;

Figure 16 The performance difference of insulating glass butyl rubber under the pump effect(thermal expansion and cold contraction)

Figure 16 The performance difference of insulating glass butyl rubber under the pump effect(thermal expansion and cold contraction)

The flexible warm edge improves the edge sealing of the insulating glass, image source Quanex (Kenex);

When consumers buy insulating glass, they generally do not directly add a warm edge to insulating glass (too extravagant). If considering the ultimate performance, more reasonable order of adding is: insulating glass / three glass two cavities → adding Single-silver Low-E Glass → Add inert gas (argon) → Warm edge → Single-silver to double-silver Low-E Glass → Finally, three silver.

Figure 17 The insulating glass TPS spacer bar

Figure 17 The insulating glass TPS spacer bar

Figure 18 The insulating glass SuperSpacer bar

Figure 18 The insulating glass SuperSpacer bar

The third plan is to use insulating glass as the basis for the addition of door and window glass, and make appropriate additions according to the home's requirements:

The first is the order of adding energy-saving thermal insulation mentioned above.

The second is when the home is faced with noise problems. If the noise itself is not a big problem, but its requirements are relatively high, you can consider adding three-glass two-chamber insulating glass to the insulating glass, which has a good energy-saving and thermal insulation effect.

If faced with low frequency noise (such as overhead, road noise), the insulating glass is mainly laminated, such as insulating laminated glass (such as 6 + 0.76 PVB + 6 + 12 A + 6), or double laminated insulating glass ( Such as 6 + 0.76 PVB + 6 + 12 A + 6 + 0.76 PVB + 6);

Figure 19 The double laminated insulating glass

Figure 19 The double laminated insulating glass

6. Other questions about insulating glass

When purchasing windows and doors, consumers will encounter many problems when choosing hollow laminated glass (to be supplemented and summarized):

1. Regarding the glass thickness of insulating glass: the size of the glass area directly determines the thickness of a single piece of glass, because, with the increase of the glass area, the rigidity of the glass must be simultaneously improved by increasing the glass thickness (laminated glass also increases the film thickness) and deflection for safe use:
As shown in the figure below, the specification requires a single piece of glass no more than 2 m², use 5 mm, and a single piece of glass no more than 3 m², use 6 mm ...That is, if a 3 m² piece of insulating glass is to be used, each piece of it must be 6 mm thick;

The specification has strict requirements on thickness. In the actual home improvement door and window market, it is not necessary to fully follow this standard (of course, businesses should follow the standard), and the standard can be appropriately lowered (this article is suitable for experienced businesses who save money for you) ), for example, a single piece of insulating glass below 3 m² is mostly 5 mm;

Because the choice of glass area and thickness also depends on the quality of the glass, whether it is filled with inert gas, local conditions, business products, and experience, you should listen to the recommendations of the business or consult professionals when making large glass;

The Maximum allowable area of safety glass

Glass type
Nominal thickness (mm)
Maximum allowable area (m²)
Tempered glass
4、5、6、8、10、122.0、2.0、3.0、4.0、5.0、6.0
Laminated glass
6.38、6.76、7.52、8.38、8.76、9.52、10.38、10.76、11.52、12.38、12.76、13.523.0、5.0、7.0、8.0

2. Regarding the price of insulating glass: the market price of an insulating glass of an ordinary area is about 150-300 yuan / square meter.

Its price is mainly affected by the cost (such as the skyrocketing price of raw materials this year), the materials used in the deep-processing glass factory and the quality of the factory, the size of the glass area at home, and the size of a single piece of glass (the larger the area, the more expensive).

3. Regarding the recommendation of the glass deep processing factory: the finished glass of a good glass deep processing factory has more guaranteed quality control, and of course, the price will be higher.

Jinan LIJIANG Glass believes that a large-scale glass deep-processing factory specializing in finished glass has the best glass quality.

The second is the glass deep processing factory/insulating glass production line set up by the door and window factory itself, and the glass deep processing enterprise with technology, scale, and equipment at the same time.

4. Regarding the sound insulation effect of the insulating glass itself: the insulating glass will not improve the sound insulation effect due to the existence of the hollow layer (the impact is small), such as the actual sound insulation value of the 5 + 5 insulating glass and the single-layer glass of 10 mm are almost the same.

If you want to improve the sound insulation effect of insulating glass, the most effective way must be to increase the configuration (three glass and two cavities, hollow sandwich, etc.), and secondly, by increasing the thickness of the glass and making a glass of different thickness (such as 5 + 6) Limit (theoretically effective, the actual difference of one or two decibels is imperceptible).

Insulating glass configurationGlass central U valueGlass center △UImprovement △U brought by argon filling
E=0.1, Air1.82--
E=0.05, Air1.700.12-
E=0.1, Argon gas1.53-0.29
E=0.05, Argon gas1.360.170.34


5. Regarding the warranty time and self-explosion warranty of insulating glass: the warranty time of general glass is the same as that of doors and windows, and no special warranty standard of 15 years will be given. At the same time, self-explosion is generally not included in the scope of the warranty. Generally, the merchant will negotiate with the seller and solve the problem by using the merchant to pay the cost and the seller to pay the labor fee.


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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