Glass and Glazing

Distinguishing features:

• Safely and securely holds large areas of glass
• High insulation and security technology
• Innovative technology
• System-tested security
• Wide range of units and opening types
• Efficient thermal and sound insulation

Glass and Glazing

South Africa is under crises from a shortage of energy and it is up to the glazing and fenestration companies to try their best to enhance the product responsible for the most energy loss in construction, glass. To this end the industry has to conform to SANS 10400-XA which pertains to energy efficiency. The calculations compare a value called U-value (the measurement of energy loss through the glass) and Solar Heat Gain Coefficient (SHGC or total radiant energy transmission) required to enhance the comfort of dwelling and energy efficiency inside your home or office building, by using different types of glass with the correct “Solar Control” in areas facing North and West. For example, utilising SIGU’s (Sealed Insulated Glazing Units) with a Low-E, or low emissivity coating, on the interior glass for all vertical glazing to keep all energy produced from an airconditioning unit in the summer or a heater in winter time inside the house, you are able to produce the same amount of comfort during summer or winter using less energy, since less energy escapes through the glass. For the best control of energy entering the house by means of heat from the suns’ infrared rays, we recommend using a glass on the exterior of the double glazed unit with a superior “ Solar Factor ”. In other words; using a glass with a slight, to heavily tint by means of either tint or pigmentation.

Trapping a layer of hydrophobic air between two panes of glass (preventing convection currents from forming) we achieve a superior insulating medium. Insulating a glass unit also reduces the emission of radiant solar energy from a warm surface to a cold body or room. Under standard conditions the insulation value of a double glazed unit with Low-E is reduced by around 67% in winter and around 64% in summer when compared to ordinary single laminated glass. Introducing Argon gas to the air gap enhances the insulation properties of the double-glazed unit even further. All the glazing products used by Fenster Aluminium adhere to SAGGA (South African Glass and Glazing Association) regulations. The most important aspect of any double glazed unit is it’s ability to insulate by means of the highest quality sealant found on the market. The best sealants are produced in Europe and are the only ones used on Fenster Aluminium products, which is why we believe in using only the best polysulfide sealant from Germany due to the consistent product quality guaranteed, ensuring the seal is consistent and upholds to the highest performance standards in the harshest environments today.

Other benefits of using double-glazed units include:
• The ability of high light transmission but still reduces heat transmittance.
• Supperior acoustic control abilities/noise reduction.
• 99,9 percent of fog buildup inside SIG units are eliminated due to the hydrophobic air made posible by the dessicant filled in each aluminium spacer upon manufacturing.
• Reducing the cost of heating and cooling throughout the year, provided all other peripherals have been attended to such as ceiling, wall and under floor insulation.

Using a 6,38mm / 12mm airgap / 6,38mm specification, the following U-values are achieved:
• 5.8 Single-glazing
• 3.6 Single-glazing Low-E
• 2.8 Double-glazing
• 2.6 Double-glazing with Argon gas
• 1.9 Double-glazing with Low E
• 1.6 Double-glazing with Argon gas and Low E

6.38mm Single Glazed

  • KW/h usage to maintain temperate in a room with Single Glazed units.

6.38mm Single Glazed Low-E

  • KW/h usage to maintain temperate in a room with Single Glazed Low-E units.

6.38mm Double Glazed

  • KW/h usage to maintain temperate in a room with Double Glazed units.

6.38mm Double Glazed Low-E

  • KW/h usage to maintain temperate in a room with Single Glazed Low-E

U-value explained

Thermal conductivity U measures the heat energy that will be transmitted through 1 m2 of material in one hour when there is a difference of 1 Kelvin across two surfaces of the material. The unit of measure of thermal conductivity is W/m2K.

The thermal conductivity of glass units depends on the type of glass used (customary glass, selective glass with different emission factors), the number of glass sheets in the glass unit, the width of air space or type of the filler gas and / or glazing film.

Uw (w = window) – overall value of the window

Ug (g = glazing) – U-value of the glazing

Ψg (linear heat transfer coefficient)

Uf (f = frame) – U-value of the frame

The heat transfer coefficient Uw relates to the entire window. This value also includes the U-values for the glazing and the frame Uf. The overall value Uw is also influenced by the linear heat transfer coefficient Ψg (g = glazing) and the size of the window.

u value -1_1

U-value of window glazing: Ug

The Ug value is a function of the type of gas filling of the intermediate space between the glass sheets, the distance between the sheets and the number of sheets.

U-value of window frame: Uf

The Uf value for the frame-sash combination is defined by means of measurement or calculation. The area for the calculation of the Uw value is the cross-section of the profile.

Linear heat transfer coefficient Ψg

The value Ψg for the edge seal of the glazing is first and foremost a function of the used material for the insulated glazing spacer. The standard material with the worst thermal properties is Aluminium. Spacers with improved thermal insulation are referred to as “warm-edge” spacers. These spacers are made of stainless steel or plastic. A larger edge cover of the insulated glazing in the sash profile further enhances the Y-value of the edge seal.

Examples of Ψ-values:

Aluminium spacer: approx. 0.08 W/m2K

“Warm edge” spacer: approx. 0,04 W/m2K

U-value of window: Uw

The heat transfer coefficient for windows and window doors Uw is usually calculated in the standard window size 1230x1480mm

size window1

Window U-value worsens as the size decreases, larger windows feature better values. This is because U-values achieved in glazing are better than in the frame material and therefore a larger glass area is able to produce a better thermal insulation value.


Uw-value calculation

The following formula is used to determine the heat transfer coefficient:


Ug = heat transfer coefficient of the glazing

Uf = heat transfer coefficient of the frame

Ψg = linear heat transfer coefficient of the insulated glazing edge seal

Ag = glass area

Af = frame area

Aw = Ag + Af

lg = length of inside edge of frame profile