Glazing a visible part of the Window

The importance of glass has been integrated in your window choice. Many solutions are available:

Double Glazing - Double Glazed Units are separated by an air or Argon Gas space to reduce heat transfer and / or sound transmittance across a part of the building envelope. In modern insulated glass units, the space between the glass panes is kept dry by the use of desiccant and the edges are sealed to eliminate possible condensation and provide superior insulating properties.

Low Emissivity - Low-E Glass has a special invisible coating bonded to the glass inside the Double Glazing Unit. This coating reduces Cooling/Heat Loss from the home, by essentially acting like a “mirror” that reflects cool air/heat back into your home. Low E can also reduce solar heat gain that can overheat your house during the warm Australian Summer, while also insulating your house from the temperature outside. Low-E glass greatly enhances the insulating performance by as much as an additional 60% compared to standard double glazing.

Toughened Glass -A type of safety glass processed by controlled thermal or chemical treatments to increase its strength compared with normal glass. Fully toughened glass is approximately 4 to 5 times stronger than heat treated glass of the same thickness when exposed to uniform static pressure loads.

Laminated Glass - Two or more panes of glass permanently bonded together with one or more interlayer. Laminated glass offers good acoustic insulation and a high protection factor against burglary.

Visible Light Transmission - VLT is the percentage of visible light passing through the glass. The higher the VLT, the more light is transmitted.

Solar Heat Gain Coefficient - SHGC, measures how well a window blocks heat from the sun. Therefore, the lower the SHGC, the lower the amount of heat gain. SHGC ratings are shown as a number between 0 and 1. The lower the number, the better the window is at blocking Solar Heat.

Heat Transfer Coefficient

The "U" thermal transmittance coefficient is the measurement unit for determining the loss of heat in a building element. It expresses the quantity of heat which crosses a square metre of a building element per second for a temperature difference of 1°C between internal and external air.

The lower the value, the higher the thermal insulation. Typical values vary between 6W/m2K for a Single Pane Glass Window to 1W/m2K for a Double Glazed Low Emission Window.

The calculation of this is based on the U-values and the size of each single material of all components. This means the glass, the frame material as well as the psi-value, which describes the heat flow generated through the insulated glass edge with the distance piece.

= U-Value Glazing (Ug) * Area Glazing (Ag)
+ U-value frame (Uf) * Area frame (Af)
+ PSI-Value * length of the edge bond (L)
/ Area glazing (Ag) + Area frame (Af)

Comparison of the heat transmittance coefficient for different glazing:

Single Glass Pane or Laminated Glass  = 5.6
Double Glazed Unit without low-e coating = 2.7
Double Glazed Unit with low-e coating = 1.2

So in summation, the lower the U-Value, the better!

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