Advantages and disadvantages of using double-glazed windows with energy-saving glass

According to heating engineers, in country houses 20-25% of heat is lost through windows, in apartments of multi-storey buildings - 40-50%. In this regard, window manufacturers take all possible measures to reduce heat losses: they use high-quality seals, multi-chamber frame profiles and double-glazed windows with different formulas, warm slopes and window sills. The problem was solved, but heat loss indicators decreased slightly.

Everything changed with the advent of low-e glass. An expert from the StroyGuru website will tell you what it is and how effectively it retains heat.

Windows on the thermal imager.

Types of energy-saving glass

1) Hard energy-saving coating (k-glass)

To give float glass energy-saving properties, a thin layer of a special metal oxide coating is applied to the surface of the still hot glass by pyrolysis during the production process on the float line. Such a coating, “sintered” with glass, is particularly durable and is therefore called “hard coating”.

2) Soft energy-saving coating (I-glass)

The production of I-glass involves applying a low-emission optical coating based on metal oxides to its surface using high-vacuum production equipment equipped with a magnetron sputtering system.

Recommendations

At the ordering stage, you must immediately find out what types of savings technology the company provides to consumers.

When accepting the finished product, it is important to read the markings on the glass.

1. The letter “m” means that plain glass was used in production.
2. “K” or “i” correspond to the type of spraying used, soft or hard.
3. The presence of film is marked with the sign “pl”.
4. "Ar" is present if argon is used as filler.
5. If there is no marking, there is air inside.

After a detailed review of the characteristics of energy-saving windows, it is easy to make a choice in favor of the appropriate type. In this case, you need to take into account the financial capabilities and features of the premises.

Advantages and disadvantages of K-glass

• The hard coating is resistant to mechanical stress and can be used even with single glazing.
• K-glass improves thermal insulation and, accordingly, heating costs, optimizes the entry of solar heat into the room, reduces condensation and also transmits light well. Externally, k-glass is similar to ordinary transparent glass. The effect of the low-e coating on light transmittance and reflection is barely noticeable.
• A “hard” coating allows you to retain approximately 70% of the heat flux incident on the window in the room.
• “Hard” coating is less efficient and more expensive, but it is stronger than soft coating, and also, from the point of view of processors, has certain technological advantages. The fact is that when assembling double-glazed windows that use Low-E glass with a “hard” coating, a number of technological operations that are inevitable when working with glass with a “soft” coating are absent. Such operations include, in particular, removing the coating from the edge of the glass to a width of about 10 mm along the entire perimeter of the panel, ensuring the required level of adhesion of the sealant to the glass in the area adjacent to the spacer frame. The hard coating does not reduce the level of adhesion, so there is no need to remove the low-emissivity layer. In addition, hard-coated glass has an unlimited shelf life and can be used in single-glazed window systems, while soft-coated materials must be used no later than 3 months after shipment from the manufacturer and are intended for double-glazed units only.

Thermophysical explanation

Someone will rightly note that not even three years have passed since I changed the windows, but they are no longer relevant, they are not the best. What now, as soon as a new product has appeared, should you immediately spend money on it? I’ll buy a film to save heat and that’s it. Although not an ideal option, it has the right to life.

Let's take a look at how thermal physics is integrated into the design of the new product. Maybe this will convince, the person will decide for himself whether it is necessary to change or not, whether the new product is worth the money or not. Moreover, let us remind you that classical wall insulation technologies are not applicable for window openings. But the advantage of new window systems is that by reducing heat leakage, the manufacturer increases the access to light.

Let's return to the physical explanation. Thermal energy travels either in the form of radiation or convection.

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Radiation - infrared spectrum, is determined by the level of surface heating. Convection is the exchange of heat between hot and cold.

Simple glass does not interfere with the infrared ray, that is, you can stick a film on it, it will reduce the release of hot heat to the street. When making energy-saving bags, at the production stage the glass is coated with non-ferrous metal sulfide and silver plating is done. They can apply a film.

The treated surface increases the level of reflection of infrared radiation by 80%. The treated glass surface transmits 72% of light, the remaining 28% does not affect perception. In summer, the surface will reflect up to 45% of solar radiation.

Advantages and disadvantages of i-glass

• The soft coating is easily deformed, so the side of the glass on which such a coating is applied must necessarily face the inside of the glass unit.
• I-glass reflects long-wave heat rays towards their emitter (that is, in winter towards the apartment where heating devices are operating, and in summer towards the street where sun-heated stones, asphalt, etc. are located), which significantly reduces heating costs in winter and for air conditioning in summer. In other words, the coating leaves heat where there is more of it.
• I-glass is superior in technical characteristics to its brother “by the letter k”. The use of double-glazed windows with i-glass allows not only to significantly increase indoor comfort, but also to reduce energy costs. During the heating season, the heat retained by a medium-sized window with i-glass is equivalent to the effect of burning 120 kg of liquid fuel.
• A “soft” coating allows you to retain 90% or more of the heat flux falling on the window in the room.
• Due to the higher energy-saving properties of i-glass, you can abandon a double-chamber double-glazed window, limiting yourself to a single-chamber one, which greatly simplifies the design.
• Low-emissivity glass with a “soft” coating is on average about 2-2.5 times more expensive than regular glass. But calculations show: due to energy savings, additional investments pay off within 1.5-2 years. It is also necessary to take into account that, along with direct payback, there are a number of factors stimulating the demand for low-emissivity glass. For example, by reducing the weight of a double-glazed window, it is possible to maintain the geometry of the window and eliminate the problem of durability of the fittings in the window frame.

Window energy efficiency class

Everyone is accustomed to seeing stickers on household appliances with a scale of their energy efficiency indicators. The same information also applies to double-glazed windows. They mean how much products of this marking allow you to save on heating and cooling (air conditioning) of the room.

Many countries have adopted standards that summarize two types of energy savings. Requirement indicators in regions with cold climates and in hot countries are different. An energy efficiency class scale has been created.

In Russia the following classification is used:

• E - low class;
• D - reduced;
• C - normal;
• B - high;
• A is the highest.

There are many different climatic regions in Russia and in each of them the requirements for double-glazed windows differ. For example, from the Moscow region, where heat and cold are average, they include the highest energy efficiency class for both the hot season and the winter.

Trends

The process of producing high-quality low-emissivity glass is quite labor-intensive and requires the highest qualifications from the manufacturer. It is no coincidence that there are only a few companies in the world that produce energy-saving glass in large volumes.

All this greatly complicates the choice of the type of coating, the use of which would be optimal in each specific case. According to experts, the higher efficiency of glass with a “soft” coating, as well as the emerging trend of reducing the cost of this material, will lead to a gradual decrease in the share of glass with a “hard” coating. Indirect confirmation of this: in Western European countries, about 80% of buildings in the enclosing structures of which Low-E type materials are used are glazed with soft-coated glass.

Where does heat loss come from?

Manufacturers' explanation:

• Particular attention is paid to the glass area. The frame is one fifth of the total area.
• Energy-saving glass is effective due to the type of glazing used: quantity and distance between glass.
• The frame material filling the inter-glass gas influences.

A two-chamber window is not effective for retaining heat due to ordinary glass. They conduct heat well, that is, they transfer it to the street equally with the room 50 to 50. To retain heat, you need to install an insulator on such bags. Low thermal conductivity is determined by the following characteristics: during the cold period, the surface cools down quickly, and with increasing humidity it becomes covered with condensation. If you see this at home, take the signal - the window design is ineffective.

Light transmittance of glass

In addition to protecting from cold, rain, noise, and ensuring air exchange, windows must provide the premises with natural light. This is one of the main functions of the window. Maintaining high light transmittance values ​​of glass ensures the most efficient use of all the benefits of natural light.

It is known that the dimensions of the glazing for each room must take into account the required level of natural illumination and light transmission. Clear glass is chosen to allow as much light as possible into the room.

Thus, the minimum light transmittance for transparent glass, depending on the nominal thickness from 2 mm to 10 mm, decreases and ranges from 89% to 79%. This figure for the most common types of double-glazed windows is already between 75% and 65%.

When applying heat-saving coatings, light transmission changes slightly and is practically no different from conventional insulating glazing. The assessment of neutrality on a scale from 0 (black) to 100 (neutral) shows that this coefficient for a double-glazed window made of ordinary glass is 99, and with i-glass it is about 98, i.e. Almost double-glazed windows are visually indistinguishable. Transparent sheet glass 4 mm thick (depending on the type of glass) transmits 85-90% of visible light, reflects about 8% and only 2-7% of visible radiation is absorbed by the glass. UV and IR radiation up to 2500 nm passes through glass only partially (approximately 75 and 80%, respectively), and at wavelengths greater than 2500 nm it is absorbed almost completely.

At the same time, the use of solar control glass with a low heat transfer coefficient makes it possible to use large areas of glazing without significant heat loss and costs for air conditioning and heating. This significantly expands the architectural and design capabilities of the design and construction of both modern buildings and structures, and those being reconstructed. To ensure a balanced microclimate in buildings and structures, it is necessary to use the sun protection capabilities of glazing.

Glass must solve not only the problems of providing people with natural light, protecting them from noise, excessive solar radiation, and moisture, but also issues of safety and structural reliability.

The coefficient of directional light transmittance of glass with solar control coating, glass colored in the mass, laminated glass with solar control properties can be significantly lower than colorless glass. When choosing a glazing option, you should calculate the number of light openings and their sizes, based on the requirements and standards for the level of natural light in the premises.

For glazing windows and balcony doors, it is mandatory to use double-glazed windows of class 1 (heat transfer resistance 0.54 - 0.64 m2.°C/W) and class 2 (heat transfer resistance 0.65 - 0.84 m2.°C/W). When constructing energy-efficient buildings, it is recommended to use double-glazed windows of class 3 (heat transfer resistance 0.85 - 1.24 m2.°C/W) and class 4 (heat transfer resistance more than 1.24 m2.°C/W).

How to install?

1. To begin with, it is worth dismantling the window , window sill, and old window frame. Installation of the window frame begins by securing it in the corners with wooden wedges (temporarily) and checking it with a level. If all is well, move on to the next step.
2. The frame is secured with anchor bolts and mounting plates. The window structure is secured with construction screws. Nails should not be used here; this may cause deformation of the product. This design is considered the main procedure.
3. The next stage is sealing , which is carried out using polyurethane foam. The surface where it will be applied should be wetted with water.
4. As soon as the foam hardens, you need to remove the temporary pegs. Next, a window sill is installed to the stand profile. The slopes are plastered both outside and inside. Then they do the painting, and after all operations the protective film is removed from the package.

Adviсe:

1. Install certain dimensions of packages (3×3.2) m; narrow spacer frames cannot be used in dimensional packages. A change in temperature will cause depressurization and its destruction.
2. The greater the distance between the glasses (25 mm), the higher the price of the product, and the thermal insulation will decrease. The optimal distance is 10-15 mm.
3. For a residential building you should buy single-chamber or double-chamber packages.

What's the difference?

What are these – energy-saving windows? Many ordinary people, buying ordinary structures made of metal-plastic, heard from sellers and managers that these are real windows assembled using this technology. During operation, many were disappointed. When installing a conventional structure made of polyvinyl chloride, the tightness will be excellent, but this greatly disrupts the normal exchange of air, which negatively affects humidity, a dew point appears and condensation occurs, which is immediately visible on the cold glass of the window.

What are these – energy-saving windows? These are structures in which the inner surface does not cool even in severe frost. So, if the temperature outside drops to -26, and inside the room is heated to the standard 20 degrees Celsius, the surface of the window maintains the temperature at 13 degrees. Of course, if the humidity in the room is very high, even this will not save you from condensation, and yet its amount will be much lower than when installing PVC windows. A reliable manufacturer will definitely tell you that these are energy-saving windows, and also explain how the design works. It must be remembered that effectiveness is maintained only if integrity is maintained.

Spraying features

No matter how many cameras there are in the window system, spraying is done only on one glass and only on one side. To ensure longer service life, the treated side is usually located inside the first chamber, on the street side. There are several varieties of layers used to save energy.

One of the most common options is k-coating. It is considered hard because it has increased strength and resistance to mechanical damage. Created using metal oxides. For application, the surface is first heated to a very high temperature, so the least resource-intensive spraying process is during the manufacture of a double-glazed window.

An alternative option is i-coating of two layers. It is destroyed to a greater extent under the influence of aggressive mechanical factors, therefore it is classified as soft. First, a silver layer is sprayed, for which the glass must be completely prepared and placed in a vacuum. The second layer – protective – consists of titanium oxide.