At the offices of the Australian Window Association (AWA), we field many calls from our members and thermal assessors using various energy rating simulation packages. Often these calls are from people who are frustrated with the out-of-date and incorrect window data in these packages. This article was written by AWA executive director Tracey Gramlick and our Window Energy Rating Scheme manager Richard Hamber to explain the issues that the industry is facing.

This is a real life window story of despair and lost opportunity for the fenestration industry as a whole.

With Window Energy Rating Scheme (WERS) member companies approaching the 450 mark, they collectively own 230,000 sets of residential window and door energy results and 200,000 sets of commercial window and door energy results.

Technically, none of these results can accurately be used in the current Nationwide House Energy Rating Scheme (NatHERS) endorsed software programs AccuRate, FirstRate or BERS. It takes an interested and glazing competent energy assessor to seek custom ratings and then use them to their best effect.

As we received the news that the new version of AccuRate is further delayed we provide this update in an attempt to explain the outstanding issues to a frustrated audience. The release of the AccuRate Program is currently in limbo as the new release, planned for the last six or seven years, hinges on the finalisation of the CHENATH engine. The release of this engine has a number of upgrades to the existing engine including the way that the AccuRate engine calculates the performance of glazing (windows) based on their Australian Fenestration Rating Council (AFRC) performance characteristics.

One of the main problems with the current system is the inclusion of a set of ‘generic’ window systems. These performance based windows (which do not exist in real life) were originally set up to define the performance of windows – allowing energy assessors to select an indicative performance intended to be matched with a real window system that is the same, or better, in terms of energy efficiency performance. This has caused a problem in the selection of a real window system as the term ‘generic’ implies that the selection can be based on the description of the window system.

As this is the case, many consumers end up with windows that match the description but will not meet the window U-value and Solar Heat Gain Coefficient (SHGC). This problem has been identified and the AFRC has worked with the government to develop a new set of default performance characteristics that can be selected in the same way as the current generics but must be matched by performance results. This project was finished in May 2011 but cannot be released until the new CHENATH engine is released.

The current engine includes performance characteristics for 2,000 custom rated window systems, which were made available by WERS for the last update to the NatHERS calculation engine.

Many users have noted that the performance values that are currently available in the software system do not match the performance of the official WERS values and that some systems are not even available to the market anymore.

This has caused much confusion in the marketplace among window manufacturers, energy assessors and consumers as to how to find equivalent products. The only correct way to meet compliance is to match the performance that is in the report to a window with an equal to or less U-value and plus or minus 10% SHGC.

The new list of over 400,000 window systems has been provided to the database developed by the AFRC to be released into the new CHENATH engine. This list will include all of the currently available WERS custom rated products and has been created using a new library builder specifically designed to be read by the new CHENATH engine.

Unfortunately, with ongoing hold ups, there is no way for this list of custom rated products to be released to assessors so that they can use them in the NatHERS programs.

FirstRate 5 and BERS Pro
FirstRate 5 and BERS Pro both depend on the release of the CHENATH engine as it is the approved standardised engine used in all three of the NatHERS programs. They also currently only include the ‘generic’ list of window products along with the shortened list of 2,000 (out-dated) custom rated products. Both of these programs require a release of the CHENATH engine before they can be released. In order to release these updates they will be required to update the calculation engine before they can include the updates.

BERS Pro has also taken one further step by publishing its own range of ‘BERS Generic Windows’. These window performance values are, according to Solar Logic, more representative of commercially available windows but cause further confusion within the industry as they are termed generic windows and have different performance values to the official generic windows available in all three of the NatHERS programs. This confusion has caused indicative window performances to be matched by description only without any verification of the real performance.

This can lead to misrepresentation of window performance and, as a result, whole of house performance. We know that the original WERS generic windows were physically ‘hotbox’ tested to confirm the underpinning simulations. We are not sure if such rigour was applied to the BERS generics.

BASIX (Building Sustainability Index)
BASIX in New South Wales has also been adversely affected by the delayed release of the new NatHERS programs. As the BASIX scheme has two methods of compliance, either using the online BASIX tools or using the NatHERS software packages, the issues above make the rating of a house with the NatHERS tools a confusing process.

BASIX has recently undertaken a project to upgrade the thermal comfort portion of its online tool. This upgrade will include the addition of the default windows that the AFRC has developed under contract for the government and see the process of selecting windows within the BASIX tool become a less confusing area. This will ensure that the selection of windows is verified with tested performance data that is accredited through the AFRC.

No doubt we will jump for joy and announce the pending release to all when it eventually happens and we close with a comment from Rodger Hills, general manager of the Association of Building Sustainability Assessors: “ABSA supports efforts to update the windows information that is embedded in the NatHERS rating tools. The current windows data is out dated and does not meet the current AFRC values used elsewhere by industry. Assessors are unable to specify commercially available windows and this creates confusion for builders and assessors alike.”