Energy Efficient Windows

Windows can play a critical role in lifting a building’s energy rating. Retrofitting older apartment buildings with modern performance glass can reduce energy consumption, while creating comfortable, light filled and secure home.Ordinary windows are an energy leak. A typical, adequately-insulated building that uses ordinary glass can lose up to 61% of heat through the windows in winter. These same windows can allow up to 86% of the solar heat gain in summer.Performance MeasuresWhen reviewing glass options, you’ll come across these standard industry measures:

• Solar Heat Gain Coefficient (SHGCw) measures how readily heat from sunlight flows through a window. The values are 0 to 1. The lower a window’s SHGC, the less solar heat it transmits. (G-value or Solar Factor is the equivalent European measure.)
• U-Value (Uw) measures the rate of non-solar heat loss or gain through a window. It includes the effect of the window frame, glass, seals and any spacers. The values are 0 to 1. The lower the U-Value, the greater the window’s insulating value.
• Visible transmittance (Tvw) is an optical measure of how much light comes in through a window. The values are 0 to 1. The higher the number, the more light is transmitted.

The Right GlassThe right choice of window glass depends on three factors: the windows orientation, how much shading they receive, and not least, your climate:

1. Hot Climate Areas (e.g. Northern Australia, including Darwin, Brisbane, and the Gold Coast)

• Preferred U-Value: low
• Preferred SHGCw: low

1. Mixed Climate Zones (e.g. Sydney, Perth and Adelaide.)

• Preferred U-Value: low
• Preferred SHGCw: mid-range (adjusted for elevation)

1. Cold climate zones (most of Victoria, ACT, Tasmania and some Southern parts of New South Wales)

• Preferred U-Value: low
• Preferred SHGCw: high (adjusted for elevation)

Window technologies

• Tinted (or toned) glass –produced by the addition of metal oxides, reduces solar heat transference and glare. As the thickness of the glass increases, so to does the intensity (or darkness) of the tint. Spectrally selective tints effectively select the visible light band from the solar spectrum (resulting in high light transmission) and filter out the UV and infra red bands.
• Low E glass – glass coated with metal or metal oxide, which increases a window's ability to insulate (low U-value and low SHGC).
• Integrated Glazing Unit (IGU) – two or more panels of glass separated by an air space and a spacer around the edges, providing thermal and noise insulation. For greater performance one of the glass panels should have a low-e coating and argon gas between the panes.
• Smart glass – also called E-glass or switchable glass, its light transmission properties alter when an electric current is applied.

StandardsAll glazing undertaken should comply with Australian Standard AS1288-2006 for the selection and installation of glass, and Australian Standard AS2047 for the selection and installation of windows.Useful linksGlass and Glazing Assoc of Australia Australian Window Association Standards AustraliaRef: Strata Community Aust