About Custom Ratings
Accredited organisations wishing to demonstrate the energy efficiency of their products comply with the Window Energy Rating Scheme (WERS). WERS enables windows to be rated and labelled for their annual energy impact on a whole house, in any climate of Australia.
The Window Energy Rating Scheme employs a combination of physical testing and computer simulation to generate energy ratings for fenestration products. WERS applies a suite of interlinked procedures including those used by the U.S. National Fenestration Rating Council (NFRC). As with the NFRC, WERS uses the software tools Window 6, Optics 5 and Therm 6. In addition to the U.S. software, several other ‘downstream', purpose-designed tools have been developed for WERS to process data, calculate performance indicators and create final reports. The tools perform different function according to the type of fenestration product being rated.
AFRC Ratings Sizes
The WERS scheme operates on three levels to convey information about the energy performance of custom-rated windows and skylights:
- Star ratings for heating and cooling
- Indicative % reduction in heating and cooling needs
- Thermal, solar and optical performance data
Most of the rating data produced by WERS is at the level of the manufactured product and is therefore valid regardless of the final building type the product is employed in. Only the WERS star ratings are building-specific and relate to the annual energy impact of the rated product on a model house. All other WERS rating data is application-independent and can be adjusted and customised for any building type, usage pattern or climate.
The data derived is available for public access in the Certified Product Directory tables attached to the member name and allows for easy comparison of windows.
The WERS scheme allows manufacturers to assist energy raters, window specifiers and consumers in the selection of the most energy efficient Windows for a home and support those who need to know if the window will enhance or degrade the house in energy and comfort terms. Energy efficient windows offer significant benefits to house owners and occupants. In addition to reducing energy costs and green house gas emissions, a properly selected window plays an important role in improving a homeowner's comfort and well being.
Key to Rating Tables
Column 1: A window ID number, for example Window 14,used as a shorthand to identify each window in many of the examples given in this chapter.
Column 2: A glazing description listing the products used to make up the glazed parts of the window, where IG (or IGU) - means insulating glass unit,usually made up of 2 glass panes with a sealed space between them,filled with air, argon or other dry gas. Note that the space is not evacuated.
3/12/3 - represents the order (from outside to inside) and the spacing between glass products, in this example a 3 mm thick glass pane,followed by 12 mm of air space or gas (argon) fill, followed by 3 mm thick glass pane; similar explanations apply to all other combinations listed.
'toned' and 'supertoned' refer to different grades of body-tinted glass products available in the market. Low-e indicates the presence of glass products with low-emittance (low-emissivity) coatings. A pyrolytic low-e coating is one type of coating technology.
Column 3: Cooling Stars when compared with the base case Generic Window 1 (3mm clear glass in a standard aluminium frame).
Column 4: Heating Stars when compared with the base case Generic Window 1 (3mm clear glass in a standard aluminium frame).
Column 5: Percentage improvement for cooling compared with the base case Generic Window 1 (3mm clear glass in a standard aluminium frame).
Column 6: Percentage improvement for heating compared with the base case Generic Window 1 (3mm clear glass in a standard aluminium frame).
Column 7:Whole-window U-value (Uw) that accounts forthe performance of the frame, edge-of-glass and centre-of-glass components. Uw is calculated for the standard sizes given in Table 1.
Column 8: Whole-window solar heat gain coefficient (SHGCw)that accounts for the performance of the frame and glass components.With SHGC, there is no distinction between centre-of-glass and edge-of-glass. SHGCw is calculated for the standard sizes given in Table1.
Column 9: Whole-window visible transmittance (Tvis).Product of glazing Tvis and glazing/frame area ratio.