About WERS

Introduction

The Window Energy Rating Scheme rates whole of window product energy efficiency performance.

The Window Energy Rating Scheme enables windows to be rated and labeled for their annual energy impact on a whole house, in any climate of Australia.

To participate in WERS, window makers must obtain energy ratings for their products from a rating organisation that is accredited by the AFRC (Australian Fenestration Rating Council)

The Window Energy Rating Scheme is managed by the Australian Glass and Window Association (AGWA).

WERS is independent of any one manufacturer and acts as a fair, rigorous and credible system for testing performance claims. WERS-rated windows must meet all relevant Australian standards. The scheme forms part of the quality assurance that smart manufacturers offer their customers. It is all about certified performance.

To realise their full potential, WERS ratings are designed to 'plug in' to NatHERS, Australia's Nationwide House Energy Rating Scheme accredited software. Similarly, the FirstRate house energy rating software from the Sustainable Energy Authority of Victoria will accept data for 'real' windows. This enables designers to 'kick the tyres' of different windows during a rating before final selection is made.

 

Why You Should Choose Energy Rated Windows

Energy Rating for windows is here to stay. The federal government's Australian Greenhouse Office helped to underwrite WERS as part of its commitment to improving energy efficiency and reducing greenhouse gas emissions from the built environment.

Home resale value, comfort and amenity are improved by the use of high-performance windows. We have moved from an industry traditionally considered as providing a commodity building material to be sold on price alone into offering true consumer goods viewed as performance appliances for energy, noise and security.

WERS conforms to the alternative solution path for energy efficiency within the Building Code of Australia.

 

How Custom Energy Ratings Are Produced

The information needed to generate a WERS rating is furnished on a commercial-in-confidence basis to the rating agency by the manufacturer. This takes the form of drawings, computer CAD files and material specifications for the window components.

Most windows can be rated entirely by a two-stage process of computer simulation. This is the preferred and most economical option. The computer modelling software is the same as that used by the U.S. National Fenestration Rating Council (NFRC). It has been thoroughly validated against laboratory tests in all climates, hot and cold. WERS is truly international in its heritage and draws on over 100 person-years of research and development in 15 countries over the last decade.

Occasionally, unusual or complex products may need to be measured by physical testing to establish their basic thermal behaviour. After initial modelling or testing, a second stage of computer simulation follows using NatHERS, from which the final WERS rating is generated.

 

History

The technical basis of the Window Energy Rating Scheme was established in 1995 under contract by Unisearch Ltd at the University of New South Wales. The foundation work was carried out by Dr. Peter Lyons and PC Thomas in the Solarch group of the UNSW Faculty of the Built Environment. Software assistance and the interface to the Nationwide House Energy Rating Scheme (NatHERS) was provided by CSIRO Division of Building Construction and Engineering. Funding was provided by the then Residential Window Association, the then Flat Glass Association of Australia and the research arm of Pacific Power.

How WERS Works

Rated windows and skylights display the WERS logo, similar to that shown below. Each rated product has a certificate which certifies that it has been energy rated.

The window star ratings for heating and cooling rank the window against alternatives, using a ten-star scale based on 17 'generic' window types. The generic windows range from very low performance to very high performance in heating or cooling. The ratings apply to the effect of the whole window including the relative contributions of glass and frame.

Rating Labels

Rated windows carry a label which certifies that the window has been rated by the Australian Window Association. The window's cooling and heating performance is rated separately on a scale of 0 to 10 stars - the more stars, the better. These stars indicate the effect the window will have on the energy performance of the whole house.

Certified Accreditation

You should also look for the label below or a WERS Compliance Certificate to certify that your window manufacturer is WERS accredited:


Example of a WERS Label

Window Ratings

To provide consumers with a simple benchmark, a comprehensive range of representative windows has been rated for their energy performance which is illustrated in terms of stars. No stars shows that the window is a very poor performer, 10 stars means excellent performance and a whole new world of energy efficiency and interior comfort. Manufacturers participating in WERS may offer custom rated high performance products which exceed the results shown below. Check the tables to see just how much benefit can be gained from a correctly selected window.

In addition, a 10 Star energy rated window will provide significant benefits in noise control and protection from fading. It is important to remember that window placement and site orientation also have an impact on the type of windows required within a house. Your WERS accredited manufacturer can advise you on the right windows to suit your home. Look for the sign that ensures your window manufacturer is WERS accredited.

Official Views

"This Government recognises the important dual role good windows can make in improving quality of life, as well as leading to a reduction in greenhouse gas emissions. I am delighted to note the commitment shown by the window and glass industries to the success of WERS. I look forward to the continued success of this exciting initiative." - Department of the Environment & Heritage

"The Window Energy Rating Scheme is an excellent example of government and industry working in partnership to address the greenhouse problem. The Australian Greenhouse office supports the introduction of the Window Energy Rating Scheme and commends the window industry for helping to reduce greenhouse gas emissions." - Australian Greenhouse Office

"Windows remain the make-or-break issue in achieving a good whole-house energy rating. WERS is the vital source of data for such windows." - Tony Isaccs, Principal Project Leader, Sustainable Energy Authority Victoria.

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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 7, Optics 6 and Therm 7. 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. 

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 pyrolyticlow-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 for the 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.

Column 10: Air infiltration rate (L/s.m2) at positive(inward) pressure difference of 75 Pa.

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How To Use Screened Products

When using the WERS screened products in energy efficiency ratings it is important to utilise them in the correct way to achieve accurate glazing performance outcomes. This page gives a guide to how the simulations were performed and how to use the performance ratings in regulatory tools such as the National Construction Code (NCC) Glazing Calculator, the NatHERS programs and the BASIX tools.

How to use the ratings in regulatory tools

To ensure that when rating a house with a screened product, using the regulatory tools for each state, you are able achieve accurate results it is important to correctly assign the performance ratings for screened and unscreened window portions. For WERS to rate the screen on specific windows it is necessary to rate the product with complete coverage of the system (pictured below).

 

If the window system utilised in the building is completely screened the WERS Screen performance rating for that window system can be used for the whole area.

If the window system contains screened and unscreened portions it is important to break the results into two distinct portions. It is important to apply the results of the screened window system to the screened portion of the window only. The image below shows an example of a window system with screened and un-screened portions.

 

 

When entering the performance values for the sample window system above the window needs to be broken into two main sections. The screened portion of the window system and the un-screened portion of the windows system. In order to insert these two different performance results into the regulatory tools the window system must be broken into three main sections with three different window performance inputs:

• The screened area of the window system: This portion of the window system can be input as one area with the performance values associated with the installed screen on the specific window that are available from the WERS screened product web page.
• The central unscreened portion of the windows system: This area of window is input with the performance values for the specific window from the WERS Database.
• The low light windows below the screened window area: These areas of window need to be split from the main area of unscreened window due to the different impact that shading can have on the window system. They can be inserted using the same window performance data as the central unscreened portion but if shading is applicable the height above the head will need to be associated with the top of the unscreened portion.

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