Use of Incorrect Performance Values
15 April 2013
Many energy ratings, particularly those entered into the free on line calculators are using glass only U Value (U GLASS) and Solar Heat Gain Coefficient (SHGC GLASS) performance results. Under the National Construction Code (NCC), within Building Code of Australia (BCA), energy efficiency provisions for Volume One, Section J2.4 Glazing and Volume Two, Section 18.104.22.168 External Glazing state that external glazing performance data must be determined in accordance with the guidelines of the AFRC (Australian Fenestration Rating Council).
The BCA guide states that:
- Glazing, for these purposes means a transparent or translucent element and its supporting frame located in the envelope, and includes a window and
- By referring to glazing, J2.4 and section 22.214.171.124 require Total U-Values and SHGCs to be assessed for the combined effect of the glass and frame. The measurement of these Total U-Values and SHGCs is specified in the Technical Manual and Procedures Protocol for Energy Rating of Fenestration Products of the Australian Fenestration Rating Council (AFRC) which has been derived from the United States of America National Fenestration Rating Council (NFRC).
Energy ratings from AFRC accredited energy raters are the only acceptable performance results for use with:
- BCA Glazing Calculators (Volume 1 and 2),
- BASIX and
- NatHERS Software tools
Not using total window system values to Australian approved procedures and environmental conditions can result in significant under performance or over performance of the building envelope, especially in buildings with large glazed areas. The stated performance of the building will not meet the energy efficiency provisions of the BCA.
Example of Uw and SHGCw that must be used for calculators
The Window Energy Rating Scheme (WERS) (www.wers.net) is the only AFRC accredited scheme currently in Australia. WERS performance data can be entered directly into the glazing calculator as total window system values.
How to ensure that you are getting a WERS (or other AFRC Certified body) certified Product.
- Can the company provide a WERS (or other AFRC Certified body) Certificate of Compliance?
- Is the company a member of WERS (Window Energy Rating Scheme)?
- Can the company direct you to a WERS listing for the product? - Located on www.wers.net
NOTE: Results pictured are samples only and cannot be used for performance results. (if in doubt please contact WERS to check the performance values).
The BCA Glazing Calculators (pictured above) is a tool developed by the ABCB in order to assist NCC users with the calculations required by the elemental Deemed-To-Satisfy energy efficiency provisions in NCC Volume One and Two. For more information of the glazing calculator please visit www.abcb.gov.au.
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