How to choose high-quality PVC windows: double-glazed windows

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What kind of glass unit will we install? This question will surely be asked by the manager you will contact to calculate the cost of the window. Of course, the specialists of the window company know the time-tested options for filling the skylight, which are suitable for your climatic zone in terms of the main parameters. Usually they are offered to the consumer, but not all people understand the importance of this element of the window system, and often they try to save money on double-glazed windows, considering their wide range to be the result of multi-stage marketing tricks.

How to choose high quality PVC windows. Part 2: double-glazed windows

It is really difficult to navigate this issue, especially since some companies that collect windows cultivate a certain confusion in terminology. Nowadays, people often refer to a whole window as a double-glazed unit (aluminum or wooden glass unit). Sometimes the assembled window block is called by the profile trademark (for example, “Rehau windows”), which inclines the developer to choose windows, focusing only on the origin of the profile system and overlooking the features of other components. And you can also hear about “double” and “triple” packages, and here it is completely unclear whether we are talking about the number of cameras or glasses.

In fact, a double-glazed unit occupies up to 80% of the window area, therefore, the functionality of the entire window system will depend on its durability and thermophysical characteristics. As a warmer replacement for single glass, double-glazed windows appeared in the 30s of the twentieth century and, thanks to their manufacturability, are now used everywhere. Now double-glazed windows are used to complete not only plastic, but also wooden, aluminum doors and windows. They are used to assemble hinged facades, used for the manufacture of interior partitions, winter garden ceilings and other spatial structures. Packages do not have to be rectangular, nothing prevents them from being trapezoidal, triangular, round, with curved sides. There are even bent (curved) double-glazed windows for the manufacture of designer windows and complex elements of a ventilated facade..

Design features of a glass unit

A double-glazed window (JV) is a prefabricated multilayer product designed to fill an opening in translucent structures. A distance frame is installed between several glasses (two or more) with a seal, then the end of the package is sealed with special compounds. The main advantage of the joint venture is the increased resistance to heat transfer: the fact is that there is an air / gas layer between the glasses, which is tens of times less heat conductive than glass.

How to choose high quality PVC windows. Part 2: double-glazed windows

In terms of thickness, double-glazed windows are from 14 to 60 mm, which depends on the distance between the glasses, their number and thickness. The most widely used joint ventures are 24, 26 and 32 mm thick. Since various profile systems have a depth-limited filling space, it is not always possible for massive packages to be installed in a specific frame..

In general, when developing a specific glass unit, the correct ratio of the area of ​​the product, the thickness of the glass and the width of the spacer frame must be taken into account – only in this way the joint venture will have the normalized spatial rigidity. For example, a single-chamber package with 4 mm glasses can be made up to 3 m2, and with glass 5 mm thick – up to 4.2 m2. In any case, the lengths of the sides of the double-glazed window must be in a ratio no more than 5: 1. The minimum size of the joint venture on one side is 300 mm, and the minimum radius of rounding of a glass unit is 100 mm.

Depending on the number of isolated chambers, double-glazed windows are divided into: single-chamber and two-chamber (designated as SPO and SPD, respectively). Occasionally, JVs with three or more chambers are custom-made, but they are too heavy, wide and expensive. Higher performance is easier to obtain using special coatings for glass, or gas filling the existing two or three chambers.

Glass – the basis of a glass unit

Modern double-glazed windows can be made from almost any type of glass, the choice is made depending on the light and insulating properties that need to be given to the finished window. It uses tinted glass, self-cleaning, with a hard and soft energy-saving coating, tempered, triplex, armored, mirror, patterned, frosted (we will tell you more about them later). By combining different technologies in one insulating glass unit, an ideal glazing with predefined characteristics is obtained. Most often, the joint venture is made of high-quality float glass with a light transparency of up to 90%, which becomes the basis for the production of the glasses listed above. Glasses of the world’s leading manufacturers are considered the best: Glaverbel, Guardian, Pilkington, Saint-Gobain – they are most often used.

The traditional glass thickness is considered to be 3, 4, 5, 6 mm; sheets with a thickness of 8, 10, 12 mm are used somewhat less often. Options with glass of 15-25 mm are available on request.

Distance frame

The frame unites the glasses into a single package, it is necessary to set the distance between the glasses, that is, the width of the cameras. Hollow closed-section profiles made of aluminum or stainless, galvanized steel are used as spacers. The metal in these zones is a cold bridge, and it is here that condensation is most likely to occur (the problem of the edge zone). Therefore, steel for these purposes (unlike aluminum, which is several times more heat-conducting) is considered preferable. However, there are also spacers made of reinforced plastic or fiberglass that allow you to create a truly warm contour around the edges of the insulating glass. These are the sensational technologies TPS (a resilient butyl frame is used) and Swiggle Strip (an insulating strip made of a wavy aluminum strip-spacer and polymer sealants is used). Also in our market there are frames with insulating polymer thermal bridges, thermal inserts from the companies: TGI, Azon, Pilkington.

How to choose high quality PVC windows. Part 2: double-glazed windows

Frame profiles are connected using corners, or bend at the corners. The second option is more effective, since there is only one joint, which means there is less chance that gas filling will be lost, or water vapor will enter the chamber..

The surface of the spacer has a perforation that faces into the inter-glass space. Spacer cavities are filled with an absorbent – molecular sieve, which absorbs moisture from the interior of the chamber. Different desiccants differ in chemical composition and do not have the same desiccant properties. As a rule, zeolite with pores up to 0.3 microns in diameter from CECA, Degussa, Grace Davison is now used. Outdated silica gel is rarely used, as it is much inferior to modern materials.

The width of the spacers used is from 6 to 24 mm, but spacers of 10-16 mm are considered optimal. When the frame is increased to 16 mm (and, accordingly, the width of the chamber), the insulating characteristics of the joint venture are improved. Further, when using a thicker frame, there is no such dynamics. But if the chamber is made wider than 24 mm, the convective movement of air / gas begins in it, and the insulating properties of the glass unit begin to decrease sharply. Too thin a frame with a large area of ​​the package can lead to the effect of “sticking of glasses”, when the air of the chamber at low temperatures is strongly compressed, and adjacent glasses, touching each other, are destroyed.


The tightness of a double-glazed window is a prerequisite for its thermal insulation, since moisture entering the air chamber increases the heat transfer rates. However, the sealant serves more than just these purposes. It is necessary to glue the glass sheets and the spacer into a single structure with sufficient spatial rigidity. Double-glazed windows with a metal spacer frame, which are common in our country, are sealed in two layers. The first, butyl, is applied in the thinnest layer (a few tenths of a millimeter) from the sides of the frame, in places of contact with the glass. Being non-hardening, it effectively stops moisture and gases. The secondary sealing layer 3-5 mm thick is applied to the end part of the glass unit. It hardens to a certain extent, but by imparting rigidity to the joint venture, it retains some opportunity for temperature shifts of the elements of the package. In this case, silicone compounds, polyurethane masses, as well as two-component polysulfides are used..

How to choose high quality PVC windows. Part 2: double-glazed windows

Performance characteristics of double-glazed windows

A double-glazed window as a complex high-tech product solves several tasks set for the window system, which we talked about in the article “How to choose windows. Basic information about modern window constructions “. In addition to providing light transparency, the working properties of glass units can be considered:

  • thermal conductivity;
  • the level of sound insulation;
  • mechanical strength (including burglary resistance and security).

Therefore, when choosing double-glazed windows for plastic windows, we simultaneously need to take into account several nuances: the climatic zone in which the translucent structure is installed; the level of street noise pressure; wind loads; number of storeys; design issues and other points.

Warm glass unit

As we have already noted, the area of ​​the joint venture is several times larger than the area of ​​PVC window elements. That is why there is no point in using expensive high-quality profile systems, if at the same time using glass units that are weak from the point of view of thermal insulation. Ideally, a glass unit should not be inferior to profiles in terms of resistance to heat transfer, and this is not so easy to achieve. The energy efficiency of a glass unit is realized in different ways, the main ones can be considered:

  1. Increase in the number of air chambers, the width of the chambers, the thickness of the glass.
  2. Use of glass with a low-emissivity coating.
  3. Filling the inter-glass space with inert gases.

Double chamber or single chamber? A double-glazed unit with two chambers transfers heat approximately 30–35 percent less than a single-chamber one, which cannot be used in heated residential premises without additional energy-saving technologies. For example, a single-chamber joint venture, made according to the scheme 4-12-4 (glass-distance-glass), differs in heat transfer resistance of about 0.37 m2° С / W, which is clearly not enough for the Russian norms, which are at the level of 0.45-0.55 m2° С / W. In turn, the package with the scheme 4-12-4-12-4 shows quite acceptable resistance to heat transfer in 0.58 m2° С / W.

A wider chamber means a warmer package. Increasing the width of an insulated chamber by 2 millimeters improves the insulating characteristics of a double-glazed unit (it does not matter, single-chamber or double-chamber) by about 10%. For example, SP 4-8-4-8-4 shows 0.5 m2· ° С / W, and 4–10–4–10–4 – already 0.55 m2° С / W. But do not forget that it is technically impossible to infinitely increase the number of chambers and the width of the air gaps, we have already talked about this above..

How to choose high quality PVC windows. Part 2: double-glazed windows

The use of energy-saving glass with low-emission optical coatings is the best way to make a glass unit more efficient in thermal engineering terms. The point is that most of the heat is lost as radiation. To return / reflect thermal energy back into the room, special compounds are applied to the glass. A distinction is made between k-glasses and i-glasses.

K-coating based on tin compounds is called hard, it is performed immediately after the sheet leaves the oven. Such glass is installed from any, even the street side of the glass unit, since the K-coating is characterized by sufficient mechanical strength and resistance to weathering and high temperatures, including tempering. So, if you use k-glass in a single-chamber package, then instead of 4-16-4 (0.39 m2° С / W), we get 4-16-4K (0.52 m2° С / W). This is almost what is needed, but in a single-chamber JV it often turns out to be insufficient, it makes sense to use K-glass in a two-chamber glass unit or in combination with gas filling.

I-coating (E-low) of several layers of rare-earth metals in a vacuum is sprayed onto the finished glass. This coating is considered “soft”, as it needs protection (such glass is placed on the side of the room, turning the spray into the chamber). Glass with soft I-sputtering is even more effective than with hard glass – a single-chamber package 4-16-4I shows 0.58 m2° С / W, and this is already the norm and even a little better.

To increase the resistance to heat transfer, the dried air inside the chambers of the glass unit is replaced with denser inert gases that prevent convection. They transfer heat from the inner glass to the outside more slowly than air. Most often these are argon, krypton, xenon and their various mixtures. Krypton is a rarer gas, but it insulates a little better than others. Gas filling itself is not very effective – insulation improvement is no more than 5%. But if you pump inert gases into a glass unit containing glass with an energy-saving coating, then it will become warmer by another 10-15%. It is worth saying that now there is a technology for manufacturing a joint venture with a vacuum in the inter-glass space, which are somewhere 20-25 percent better than their air counterparts and quieter..

Soundproof properties of glass units

If special requirements for sound insulation are imposed on the PVC window block, then special double-glazed windows should be used to fill the skylight. First of all, the width and number of chambers have an impact on the resistance to noise pressure. The dynamics are as follows:

  • increasing the distance between the glasses by 2-4 mm, the sound insulation coefficient improves by about 10 percent;
  • a two-chamber joint venture is quieter than a single-chamber one by about 40-45%.

How to choose high quality PVC windows. Part 2: double-glazed windows

Using gas filling also optimizes the acoustics of the glass unit. For example, SP 4-16Ar-4K has a coefficient of 35 dB, while SP 4-16-14K has only 28 dB.

Good performance is achieved by using an asymmetrical insulating glass design that prevents resonance from occurring. In this case, you can manipulate both the width of the cameras (using spacers of different thicknesses) and the thickness of the glass. Here is an example: SP 4-8-4-8-4 shows the coefficient up to 37 dB, and SP 4-6-4-10-4 – up to 40 dB.

Also, sound waves are quite effectively damped by glasses with various polymer layers, such as triplex. Some glass companies have developed special acoustic films.

Safe double-glazed windows

During operation, glazing is exposed to various mechanical and temperature influences. Glass is a fragile material that, if broken, can cause serious harm to a person. To neutralize this danger, insulating glass units with tempered glass are used, as well as laminated and reinforced products..

Tempered glass is heat treated similar to metal tempering. As a result, the mechanical resistance of glass increases several times (to impact, stretching and deflection), and when broken, it crumbles into many small pieces. It is interesting that you can temper any glass (colored, tinted, energy-saving with K-coating), while it does not lose its insulating and light transmission characteristics. It is logical to use such glazing in children’s rooms, in massive windows, at a height.

How to choose high quality PVC windows. Part 2: double-glazed windows

Laminated products (triplex and polyplex) consist of several glasses, which are connected over the entire area with a polymer film or polymer resin. The highlight of this glass is that when destroyed, the fragments do not scatter, but remain on the elastic film. It is on the basis of triplex that bullet-resistant and armored glasses are made. Triplex glasses significantly improve the resistance of the window block to force burglary. By combining various glasses and films in triplexes, we get packages with original visual and functional effects. Triplex is good where there is a danger of intruders entering through the window – summer cottages, cottages, apartments on the first and last floor.

Reinforced glass has a metal mesh in its structure, which also prevents the formation of fragments in the event of a glass unit break. Naturally, such products are distinguished by increased strength, they are often used as fire-fighting in public, technical and industrial premises. Reinforcement lends itself to transparent, patterned, corrugated glass.

Insulating glass units for sun protection

We do not always need to collect heat; in the summer, the opposite situation arises, when the room heats up too much. The problem can be exacerbated by the presence of a low-emission coating, which creates a thermos effect. There are several options for resolving the issue.

How to choose high quality PVC windows. Part 2: double-glazed windows

Tinted glass is obtained by adding metal oxides to the melt. They have a blue, green, bronze, gray shade, visible both outside and inside the room. JVs with such glasses absorb up to half of the solar energy entering the room, they hardly reflect the rays and do not glare. Tinting can also be carried out on the glass surface, as a rule, this is a hard coating made of a metal or oxide layer..

There are glasses that, being transparent, reflect the heat rays of the sun, but let natural light into the room. Reflective glasses with a mirrored coating work well against the sun, by the way, they are very practical to protect from the gaze of strangers (first floors, special rooms).

Additional elements inside the air chamber

The developers of double-glazed windows came up with the idea of ​​using the inter-glass space in order to place auxiliary elements of the window system there. A striking example is a decorative layout (shpros), which helps to visually diversify the appearance of a plastic window. Shpros with a width of 8 to 26 mm are fixed to a spacer frame with a thickness of 12 mm during the assembly of the glass unit. The strips can have different colors, but the most popular are white, brown, bronze, gold, silver. There is a lot of room for imagination in terms of creating an unusual layout configuration, since there are a lot of different connecting elements.

How to choose high quality PVC windows. Part 2: double-glazed windows

An interesting modern technology is built-in blinds and roller blinds that do not need to be looked after. Lamellas and canvases can be installed in any glass unit, the main thing is that the chamber width is from 20 to 27 mm (depending on the manufacturer). The shutters inside the package can be rotated to any angle and raised / lowered. The control rod of the mechanism is displayed on the window profile, there are systems with magnetic control knobs, there is an electric remote drive. Qualitatively assembled double-glazed windows with built-in shutters do not lose their insulating characteristics, they remain sealed, some manufacturers fill them with inert gases.

Who produces double-glazed windows

Large window firms assemble double-glazed windows themselves, being able to control product quality. Many profile converters order glazing from specialized companies that operate on automated lines using only high-quality parts. Unfortunately, there are joint ventures on the market that are assembled by handicraft from components of unknown origin. You can distinguish these products on your own, for example, if you use the provisions of GOST 24866-99 “Glued glass units for construction purposes”. With the help of the simplest tools, a glass unit not attached to the window is examined, you need to pay attention to the following points:

  1. Product marking should include information about the manufacturer, types of components, production date.
  2. The presence of chips, chipping, air bubbles and other defects of the planes and end of the glass is not allowed.
  3. Internal non-hardening sealant must not penetrate the chambers.
  4. The outer sealing layer must be even, without tears and sagging.
  5. It is necessary that the camera is free from moisture.
  6. The limiting difference in the lengths of the diagonals is no more than 3 mm for windows with a side of 1.3 meters and 4 mm for windows up to 2.3 m (measured with a tape measure).
  7. The permissible deviation of the thickness of the glass unit is up to 1 mm (check with a vernier caliper).
  8. For a distance of no more than a millimeter, the glasses can be displaced relative to each other (we attach a square to the end).
  9. The package must be flat, an even rack level (about a meter long) or a rule is applied to it.
  10. By visual inspection we determine the transparency of the glasses, the presence of optical distortion.

How to choose high quality PVC windows. Part 2: double-glazed windows

At the company where you are going to order windows, ask whose production of double-glazed windows they use, what components they use, what equipment they assemble – the efficiency of the window unit directly depends on this. This is all that we wanted to tell about double-glazed windows, in the next article we will talk about fittings for PVC windows.

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