Specifying Glass for Energy Efficiency

Specifying energy efficient glass is getting easier. Design software such as AccuRate, FirstRate 5 or BERS pro is assisting the industry to not only specify high performance glass and window types, but it's actually educating on factors such as orientation, eave placement and whether to have louvers or fixed lites.

Three Simple Guides to glass selection in your climate zone are now available for download. The guides, developed with information from the Sustainable Windows Alliance project (SWA), provide information to assist you with specifying the most sustainable glass and windows in your climate.

The three guides cover cooling areas (BCA Climate zones 6, 7 & 8), heating areas (BCA Climate zones 1, 2 & 3) and mixed areas (BCA Climate zones 4 & 5).These downloads are available below.

 

Importance of SHGC and U Value
As long thought by many in the industry, the SWA’s findings demonstrate that SHGC (Solar Heat Gain Coefficient) and U Value are critical considerations when specifying windows and glass.

As shown in the table following, extracted from the SWA report, a low U Value is generally preferable regardless of climate, whereas SHGC should be based on the climate as well as the orientation of the windows.

In cooler climates, north facing windows should have a high SHGC to allow for passive solar energy in winter; fixed shading should be designed to shade the windows during summer. East and west facing windows should have a low SHGC to avoid overheating in summer. In hot climates, a low SHGC is always ideal.

Climate

Considerations

Preferred U-Value

Preferred SHGC

Other Factors

         

Hot - Zones 1, 2 & 3

WA, NT, QLD

Areas included in these climate zones are Northern Australia, Brisbane and Darwin.

  - Keep solar radiation out of the home.

  - Retain coolness of air conditioned air

    Low

 Low

 - Windows with high      openable areas to  maximise opportunity  for air movement for    natural cooling

         

Mixed - Zones 4 & 5

NSW, WA, SA

Areas included in these climate zones are Sydney, Perth and Adelaide.

 

 - Balance the benefits of  solar heat gain in winter  against keeping cool in  summer.

   - Use midrange solar    control Reduce heat  flowing through windows  (in both directions) over  course of year.

   Low

 Mid-range (or ideally      tuned by elevation)

 “Season-specific”    physical shading of  windows (e.g. eaves  over North-facing  windows). Windows with  adequate openable area  for ventilation

         

Cold - Zones 6, 7 & 8

VIC, ACT, TAS, NSW

Areas included in these climate zones cover most of Victoria, Australian Capital Territory, Tasmania and some Southern parts of New South Wales.

  - Maximise solar heat  gain for majority of year

    Low

 High

“Season-specific”  physical shading of  windows (e.g. eaves  over North-facing  windows).

 

For further information on SHGC and U-Val performance figures of specific whole-of-window systems check out www.wers.net, or for further details on Australia's window energy rating body, visit www.afrc.org.au.