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energy

SOLAR CONTROL • PROTECTION AGAINST ULTRAVIOLET (UV) RADIATION

SOLAR CONTROL

Energy and light factors are interrelated in the following ways:

fire With the use of specially coated reflective glass, increasing the level of reflected solar radiation. The amount of absorbed solar radiation remains high, as is the amount of secondary emission of infrared radiation (heat) both externally and internally.
fire With the use of colored or specially color-coated glazing, or by means of colored interlayer in laminate glazing, which increases the levels of radiation absorption and infrared radiation (heat) emission, while limiting light transmission.
fire With a combination of reflective and absorbent glazing, carefully selecting the pros and cons of each configuration.

Taking the above methods for solar control into consideration, the following types of glass can be used:

  • Solar control energy glass
  • Low emissivity energy glass

PROTECTION against ULTRAVIOLET (UV) RADIATION

Glass panes are highly transmissive mediums of solar radiation. However, the addition of an interlayer in a laminated glazing unit can result in high levels of absorption of the harmful ultraviolet radiation. Laminated glass exhibits excellent durability over time and against weathering, while offering constant protection against UV radiation, even under conditions of prolonged direct exposure to solar radiation.

The transmission, reflection and absorption drivers for both light and energy performance depend on the types of glass and interlayer. UV radiation is responsible for the fading of colors of furnishings in the interior of buildings, however the use of laminated glass, with the ability of PVB interlayer to block this type of radiation, successfully addresses the problem. Finally, when it comes to human well-being, one cannot overemphasize the importance of protection against UV radiation-induced sunburns and other skin irritations.

VAS GLASS, through its certified range of laminate glazing products, offers 99.9% levels of defense against UV radiation.

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INSULATING GLASS

Insulating glazing is ubiquitous in building construction. The effort of architects and engineers to integrate buildings into the natural environment spawned demand for a wide range of glazing systems. Over time, an additional goal has been added: the conservation of energy for heating and cooling both in new and renovated buildings.

VAS GLASS, in line with architectural, construction and environmental demands, offers its two distinct insulating glazing product lines, certified (CE marked) according to the European Norm EN 1279, under the VAS-ENERGY and VAS-SOLAR brand-names.

The proper combination of these glazing systems can satisfy the requirements of even the most demanding technical specification for a building.

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1. Monolithic glass
2. Low emissivity coating (if applicable)
3. Cavity (under vacuum, or filled with Argon, or Krypton, or Xenon)
4. Initial butyl-based sealing
5. Spacer
6. Desiccant (silicone based)
7. Secondary sealing compound (polysulfide, hot melt, or silicone)
8. Coating position

SOLAR FACTOR

Represents the percentage (%) of the total incident radiation transmitted directly or indirectly through the glazing to the inside of a building.

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SOLAR CONTROL GLAZING

The use of solar control glazing results in the reduction of solar gain and thus, the reduction of the energy requirements for cooling. The image below depicts the difference between an ordinary monolithic glass and solar control glazing.

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LOW HEAT‐TRANSFER GLAZING

Heat-insulating properties of a double glazing unit

The cavity between two glass panes significantly impedes the transfer of heat from the warmer to the colder pane due to the low conductivity of the air space or the cavity-filling gas. This, in a sense, is the advantage of double over single glazing, whereby unobstructed heat transfer via conduction takes place within the monolithic glass.

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Heat-insulating properties of double glazing with low-emissivity glass panes.

The cavity between the two panes significantly inhibits the transfer of heat for the warmer to the colder pane due to the low conductivity of the air space or the cavity-filling gas. The low-emissivity coating inhibits radiated heat transfer between the two glass panes.

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MEANS OF IMPROVING UPON HEAT-INSULATING CHARACTERISTICS

  • Increasing the cavity width (up to a certain point).
  • Using low-emissivity coated glass (low-e).
  • Filling the cavity with a less conductive gas, compared to dry air.
  • Reducing convection within the cavity.
  • Creating conditions of partial or total vacuum within the cavity.
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ENERGY EQUILIBRIUM – TOTAL HEAT EXCHANGE
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Low emissivity coatings prohibit radiation exchange for the long-wave infrared radiation region of the spectrum.

Heat loss reduction. Low emissivity coatings transmit solar radiation in a range starting with UV, up to and including visible light wavelengths until they approach the infrared region of the spectrum.

Solar heat gain. Energy equilibrium is:

Striking a balance between heat loss and solar gain.

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EXAMPLES OF HEAT EXCHANGE

WINTER: HEAT LOSS

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1. Warm air from the interior comes in contact with the colder inner surface of the glass pane, removing heat away from the air, leading to the gradual cooling of the interior space as the air naturally mixes.

2. Heat is conducted through the mass of the glass pane towards its cooler outer surface.

3. Cold air from the exterior comes in contact with the warmer outer surface of the glass pane. Heat is transferred to the colder air and is diffused in the environment.

SUMMER: HEAT GAIN

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1. Warm air from the exterior comes in contact with the colder outer surface of the glass pane. Heat is transferred and heats up the colder glass pane.

2. Heat is conducted through the mass of the glass pane towards its cooler inner surface.

3. Cold air from the interior comes in contact with the warmer inner surface of the glass pane, warming up the air, leading to the gradual heating of the interior space as the air naturally mixes.

SPECTROPHOTOMETRIC FEATURES

When the sun’s rays hit the glazing, a fraction of the solar radiation is reflected outwards, another fraction is absorbed by the mass of the glass and another fraction is directly transmitted in the interior space. The ratio of each such part to the total incident radiation defines the energy reflection, energy absorption and energy transmission factors.

There are two categories of factors that specify the optimal selection of components for insulating glazing:

A. SOLAR ENERGY FACTORS

- DET or τe (EN 410): Direct Energy Transmission, represents the fraction of solar energy in the infrared range of the spectrum that is directly transmitted in the interior through the glazing.
- EA or αe (EN 410): Solar Energy Absorption, represents the fraction of solar energy in the infrared range of the spectrum that is absorbed by the glazing unit.
- ER or ρe (EN 410): Solar Energy Reflection, represents the fraction of solar energy in the infrared range of the spectrum that is reflected outwards by the glazing, back to the environment.
- Ug (EN 673): Thermal transmittance is a glazing insulation index, as it reflects the rate of transfer of heat passing through the glazing, from the warmer to the colder areas. The lower the thermal transmittance value, Ug, the higher the thermal insulation of the glazing system.
- SF or g (EN 410): The Solar Factor represents the total amount of transmitted solar energy (g-value) and is equal to the sum of solar energy directly transmitted through the glazing unit and the solar energy initially absorbed by the glazing and emitted back to the interior space.
- SC (EN 410): The Shadowing Coefficient represents the ratio of the total amount of transmitted solar energy (g-value) to the solar energy (g-value) which passes through 3mm clear float glass (which is 0,87).

B. SOLAR LIGHT FACTORS

- LT or τv (EN 410): Light Transmission factor, is the fraction of solar radiation in the visible light region of the spectrum, transmitted through the glazing into the interior space.
- LR or ρv (EN 410): Light Reflection denotes the fraction of solar radiation in the visible-light region of the spectrum, reflected outwards by the glazing back into the environment.
- LA or αv (EN 410): Light Absorption represents the fraction of solar radiation in the visible-light region of the spectrum absorbed by the glazing.

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(A) Incident solar radiation
(Β) Reflected solar energy ER or ρe (EN 410)
(C) Solar energy emitted outwards (following absorption) qe
(D) Reflected light LR or ρv(EN 410)
(Ε) Absorbed light LA or αv (EN 410)
(F) Transmitted light LT or τv(EN 410)
(G) Directly transmitted solar energy DET or τe (EN 410)
(H) Solar energy emitted inwards (following absorption) qi
(Ι) Solar factor SF or g (EN 410)
(J) Absorbed solar energy EA or αe (EN 410)

The following factors are also important:

C. EMISSIVITY

Glazing has the ability to absorb and re-emit solar radiation in the form of heat. The emission takes place in both directions relative to the glazing plane, inside and outside of the building, resulting in heat loss. The value (e) denotes the emissivity of the glazing system. The emissivity of a glazing system can also be expressed in terms of how absorbent it is.

The lower the emissivity (therefore the absorption), the higher the solar energy reflection, and therefore the higher the heat preservation in the winter, or the heat reflection in the summer, resulting in thermal comfort. The advent of thin-film pyrolitic coatings applied to the raw soda-lime glass represents a significant improvement in thermal efficiency by lowering the emissivity value (e) of the glass.

However, emissivity affects only long-wavelength infrared radiation while, by contrast, has virtually no effect on solar radiation. To combine thermal insulation with solar control, other types of coatings must be used which combine these two functions. Glazing emissivity (e) measurements are performed according to European Norms EN 673 and EN 12898.

Δ. ΕΠΙΛΕΚΤΙΚΟΤΗΤΑ

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The solar energy entering a given space comes entirely from solar radiation (visible light, ultraviolet rays, and infrared radiation). The amount of solar energy entering a building can be limited by using high-performance coated glass, which without significantly reducing light transmission levels, prevents UV and infrared radiation from passing through, while letting visible light in.

The ratio of a glass light transmission (LT) and its solar factor (SF) is its selectivity. The closer the value of the ratio is to 2 (or higher), the more selective the glazing.

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ΕΠΙΔΟΣΕΙΣ ΕΝΑΝΤΙ ΚΛΙΜΑΤΟΣ

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BENEFITS OF USE OF COATED GLAZING IN BUILDINGS

fire TEMPERATURE CONTROLLED BUILDINGS

  • Year-round energy conservation, lower expenditure in air-conditioning.
  • Smaller air-conditioning units, lower capital expenditure.
  • Smaller CO₂ footprint.

fire BUILDINGS WITHOUT AIR CONDITIONING

  • Energy conservation and cost savings during winter.
  • Smaller CO₂ footprint.
  • Comfort during warm periods.

fire ALL BUILDINGS

  • Optimal light transmission / control.
  • Energy conservation and cost savings for artificial lighting.

ΠΙΝΑΚΑΣ ΕΚΤΙΜΗΣΗΣ ΙΔΑΝΙΚΗΣ ΥΑΛΩΣΗΣ

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SPECIAL GLAZING FOR EVERY APPLICATION

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  • Regulation requirements
  • Climatic zones
  • Building orientation
  • Size of openings
  • Building use

Consequently, the parameters that ultimately determine all these values for a given level of incident solar radiation are glazing color, glazing width and in the case of coated glass, the characteristics of the coating. Significant improvement over the thermal transmittance of double glazing was achieved through the replacement of air with noble gases (krypton, argon, xenon) which exhibit both lower conduction and convection properties, inhibiting heat transfer and heat loss, either by contact or through the air.

VAS GLASS offers high performance insulating special glazing systems able to satisfy the technical requirements set forth in any given project’s specification, combining readily available glass substrates from its vast selection in stock.

Proper combinations of various glasses can exhibit the following characteristics:

  • Solar control, from combinations with VAS-SOLAR glazing.
  • Thermal insulation, with combinations of low-emissivity VAS-ENERGY SAVING glazing.
  • Reduced window cleaning and maintenance frequency, with combinations of self-cleaning or self-cleaning treated glass.
  • Sound control, with combinations of VAS-SAFE ACOUSTIC glass.
  • Decoration, with combinations of VAS-SAFE COLOR laminates and tempered VAS-PRINT CERAMIC glazing.
  • Safety, with combinations of VAS-SAFE laminate glazing.
  • Protection, with combinations of tempered VAS-SEC or heat strengthened VAS-HS.

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  +30 22210 52607, +30 22210 53607

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