Saving energy can also be achieved with smartly designed glazing

We are standing right by the production line. What can we see here?
The production of insulating glass begins at the cutting table, where the glass sheets are cut to the desired size. From there, they are transported by an automatic rolling carrier to so-called libraries, which are special shelves or stands where the glass is temporarily stored until it is replenished into the automatic production line – precisely according to the production cycle. Once the individual glass sheets are on the line, they move to the segment where their edges are polished, and then proceed through a washer and dryer to the stacking station where an operator installs spacer frames. The glass then goes into the chamber press, where two or three sheets are glued together under pressure – in a protective atmosphere of argon – depending on whether we are producing double or triple glazing. This is then sealed with a special secondary sealant – polyurethane or polysulfide.

By the way, the placement of the spacer frame is the only moment in the entire production process where manual labor is required. Otherwise, the production is fully automated, which reduces the risk of glass damage or injury. A huge advantage is also the speed of production – it is thirty to forty percent higher compared to a standard line where glass is loaded manually.

What happens if the production operator accidentally touches the cleaned glass while placing the spacer frame?
A small mark can be “polished out” to a certain extent, but due to the coating on the glass, this is problematic. It’s worse when a “smudge” or dust particles appear inside the glass, between the laminated sheets. If the quality inspector then determines that the glass exhibits more defects than the standard allows, we must dispose of it.

Can you still utilize it, recycle it?
We cannot, but there are many recycling companies that can separate flat glass from other materials and use the shards to produce, for example, insulation materials.

Are there orders where you can't do without manual labor to a greater extent? For example, in the case of producing glass of atypical shapes or dimensions?
For smaller glass sizes, we can also produce atypical shapes like trapezoids or triangles on the automatic line. Larger formats are produced on a special project line, where the glass is loaded manually using a suction frame.

How often do you work on non-standard projects?
If I were to quantify it as a percentage of production, it's about up to five percent. In ninety-five cases, we are dealing with rectangular elements.

Where is flat glass used?
About sixty percent of flat glass is processed for the manufacture of windows, glass facades, mirrors, decorative glass, glass interior partitions, and so on. Glass can come in various colors – the most common is clear float (flat glass, note of the editor), but there are also extra clear glasses that have the maximum amount of iron oxide removed, so they do not have that typical green tint. Additionally, glass with special coatings is produced that can either reflect sunlight or let it pass through to a greater extent. The remaining approximately forty percent of flat glass is used in the automotive industry.

You say that the coating can influence the thermal transmittance of the glass, or rather its solar factor. How does this work in practice? What options do architects and designers have if they want to choose from the HELUZ IZOS offering?
When designing a house, its orientation towards the cardinal directions plays a crucial role. Generally, the southern orientation is used, which lets in the maximum amount of daylight into the interior, but during summer also excessive thermal gains. If the windows on the southern side of the house cannot be shaded by any means, whether by the geometry of the building, such as some overhang, or external shading, we can use insulating glass with anti-solar coating – in our offering, this is the IZOS Shadow triple glazing, which allows a maximum of thirty-five percent of solar energy inside. This is at least a third less than ordinary glass.

In cases where southern windows can be shaded, we can instead use insulating triple glazing IZOS Energy+, which maximizes solar thermal gains up to sixty-two percent, allowing us to save on heating during the winter. Then in summer, we can simply shade these windows with, for example, external blinds. For the windows on the northern side, we can use regular triple glazing. The advantage of today’s anti-solar glasses is that they are color-neutral and can be combined within one building with the ordinary ones without compromising the aesthetics of the house.

How much can be saved annually on energy through properly designed glazing?
It can be several thousand korunas. You can even calculate it on our website using a special calculator.

The acoustic insulating properties of windows also play an important role in their design...
First of all, it is necessary to say that the acoustic parameters of the window need to be addressed right from the beginning, as they determine the thickness of the frame, the geometry and thickness of the glazing bead, the type of hinges, and others. The ability of insulating glass, or the whole window, to dampen noise from the outside environment is determined by what is called the air sound insulation index (Rw, note of the editor) given in decibels. The higher this value, the better the window isolates noise. Ordinary triple glazing can dampen sound by thirty-three decibels, and the maximum value of air sound insulation in sound insulating triple glazing is fifty-four decibels.

Acoustic glazing should always be designed with regard to the specific conditions of the environment in which it will be installed – that is, not only considering the intensity of the sound but also its frequency. If you live, for example, near a road with slow traffic, where low-frequency noise spreads, it will be necessary to design a different solution than in the case of high-frequency noise, such as the sound of the human voice.

It’s also good to know that acoustic glasses are often laminated, so they are also safety glasses. The film that holds them together also serves as a one hundred percent UV filter, which has a positive effect on the color stability of interior furnishings and especially on human health.

You mentioned laminated or layered safety glasses. In addition to them, there is also thermally toughened glass, or it may be a combination of both technologies. What is the difference in their use?
Thermally toughened or tempered glass has enormous strength. Compared to ordinary float glass, it is much stronger in tension under bending, so you can bend it into small radii and it withstands wind pressure or strong lateral impacts. That is why it is used to manufacture safety glasses installed in places where there is a risk of injury or where high-strength glass is required. For example, it is used to make barriers for ice surfaces, which are sometimes wrongly referred to as plexiglass. If tempered glass breaks, it does not shatter into the typical sharp shards that can cause serious stab-like injuries but breaks into small pieces that do not fatally injure you.

Thermally toughened glass is also resistant to extreme temperatures, and you can find it, for example, in oven doors. In architecture, it is most often used for glass facades that are exposed to sunlight, and if the glass were not tempered, it could crack. By the way, if you have sunglasses with a polarizing filter, you can tell whether the glass is thermally toughened...

How?
You will see dark spots on it – sometimes called “leopard spots” – which are points with different tension along the cross-section of the glass. This phenomenon is scientifically referred to as anisotropy. It is well visible, for example, on car windows.

During one of your webinars, you pointed out that architects often place radiators near fully glazed walls, which can lead to glass failure due to thermal shock. Do you encounter other such mistakes in practice?
This is a relatively common mistake. The radiator temperature can reach up to sixty degrees Celsius, so if the heating is placed just a few centimeters from the fully glazed wall, the glass may crack. This obviously does not apply if it is thermally toughened.

The second major mistake I encounter is that designers do not respect safety standards when designing insulating glasses. If a window has a low sill, that is to say, down to eighty-five centimeters, or it has none at all, it must fulfill the function of a railing under certain conditions – that means it must have a safety function against falling (ČSN 74 3305 – Protective railings, note of the editor). This is ensured by the combination of toughening and laminating. I dare say that it is not the case in up to ninety percent of instances.

The safety of glass is tested using a pendulum, a steel ball, or an axe. What can the most durable glass you are able to produce withstand?
We specialize in basic safety, that is, against injury and against forced entry. Glass secured against forced entry is offered up to security class P5A, which is stipulated by the ČSN EN 356 standard. This glass is tested by dropping a steel ball from various heights. Glasses designed to protect users from injury are fitted with a double film that keeps shards together in case the glass breaks. This glass is tested by a pendulum drop. Here, according to the ČSN EN 12 600 standard, the highest class 1B1 can be achieved.

What is the weight of this pendulum?
The pendulum weighs fifty kilograms and is covered with two tires that imitate the softness of the human body. For us to label the glass with class 1B1, it must withstand the fall of the pendulum from a height of one hundred and twenty centimeters – it can break, but the pendulum must not pass through. Higher security classes, where the glass is fitted with more films, are tested with a lab axe, and of course, there are glasses that can withstand bullets or explosions. But that is each manufacturer’s know-how.

When selecting insulating glass, not only its functional properties but also aesthetics play a role. The trend in recent years has been digital printing. Can you explain what possibilities this technology brings to architects and designers?
Digital printing allows any motif or photograph to be applied to the glass, up to 4K quality. The customer can use either our database of photographs or send us their own if they have the required quality for the desired format. Digitally printed glass can be used as an image or a backsplash above the kitchen countertop; however, it is not very suitable for backlit applications, where defects may appear that would otherwise not be visible. Currently, we are testing which colors can be used for backlighting – for instance, shades of blue do not contain these aesthetic details, while red is very problematic. It’s alchemy.

How does this method of decorating glass differ from the enameling technology that you also offer?
Enameling is used for solid color coating of glass in any RAL shade. The color is applied using rollers through which the glass passes, whereas with digital printing, it is applied through a nozzle.

At the beginning, I asked you about the production of glass in non-standard formats or shapes. What has been the most atypical order you have encountered so far?
It was definitely the insulating glasses for the facade of the University of Sheffield, which my colleague Petr Hýpal can tell you more about, as I wasn't working here at the time. Regardless, it is still talked about today…

Petr Hýpal: Yes, this order was non-standard in every respect. It involved triple glazing of irregular shapes with anti-solar protection, some tempered, some semi-tempered… The glass had a special milky film, was variously ground, and had different levels of embedding into the modular facade. Some were even protruding. Each piece had to be manufactured in a precise order so that each stand with finished glass corresponded to one module on the facade – there were about eight hundred modules. The individual insulating glasses were very diverse in shape. They were various polygonal shapes, so their assembly, which had to be absolutely precise, was a very challenging task for the production operators.

How long did the production of all the glass take?
Petr Hýpal: At least a year. If it had been standard rectangles of a similar format, we could have produced about a hundred pieces during a shift. As it was, in some cases we produced only about ten a day. Additionally, because the glass was intended for the British market, where they have different regulations, all of it had to be specially marked. The final inspection was also very demanding, so it involved not only our quality inspectors but also a representative of the client.

HELUZ IZOS
www.izos.cz
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Photo: Michael Tomeš