Designers Specifying Glass for Energy Efficiency
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.
Australian Climate Zones Map
Image sourced from BCA 2010, courtesy of the Aust. Building Codes Board www.abcb.gov.au
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). |
Glass Selection Guides for Each Climate Zone
Guide to Glass Selection - Climate Zones 1, 2 & 3 (Heating areas)
Guide to Glass Selection - Climate Zones 4 & 5 (Mixed areas)
Guide to Glass Selection - Climate Zones 6, 7 & 8 (Cooling areas)
Unsure of how window performance figures work? See Energy & Glass - How it Works
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.