The Australian Fenestration Rating Council lists all the factors that must be taken into account when considering the design of a building and replacement of window systems. Fenestration plays a significant role in buildings, but what exactly is fenestration and how does it make a positive impact?
Fenestration is the arrangement and design of windows and other glazed elements in a building. It can often be the most impressive feature of a building and covers a range of products, including windows, curtain walls, skylights, window films and glazed doors.
The Australian Fenestration Rating Council (AFRC) is the Australian body that provides independent verification of fenestration product performance. It develops, administers and approves the only uniform, independent, comparative rating and labelling system for the energy performance of windows, doors, skylights and attachment products. Its scheme allows windows, skylights, glazed doors and applied treatments to be tested for their performance in a comparable manner, so that buyers can select the best product for their building.
The AFRC measures the energy performance of fenestration products in three different and important areas. These are the U-Value (UW), Solar Heat Gain Coefficient (SHGCW) and Visible Light Transmission (VTW). These three measures are of great importance when considering the design of a building and replacement of window systems to ensure the comfort, liveability, amenity and energy performance of a building.
So what do these different values mean?
The U-value is about heat transfer. This occurs when there is a difference between the temperature outside and inside. Heat can be lost or gained through conduction, radiation, convection and air leakage. The total of this heat transfer is expressed as a U-Value. The lower the U-value the better the window protects from heat transfer. Basically, the U-value is the insulation provided by the fenestration product. The U-values that are used are whole of product values, meaning that the U-value is for the combination of the frame and glass. These are correctly written as Uw but are generally just called U-values.
Windows also react thermally through direct and indirect radiation. When sunlight (radiation) hits a window, it transfers heat through it. Solar Heat Gain Coefficient (SHGC) is the measure of the amount of solar heat that passes through a window. The rating is measured between zero and one – zero meaning that none of the available solar heat will pass through the window, and one meaning that 100 percent of the available solar heat will pass through.
Visible Light Transmission is the amount of light that is transmitted through a fenestration product, giving natural light to the inside of a building. Not unlike SHGC, VT is measured as a coefficient where zero implies that none of the available light can pass through the window system and one implies that 100 percent of the available light can pass through.
How can you use rated fenestration products to boost the performance of buildings?
To achieve optimal energy savings, amenity and comfort of the building facility managers should look out for various factors when replacing a fenestration product.
Climate affects the selection of fenestration products. Different climatic conditions require different levels of performance associated with that specific climatic zone. The Building Code of Australia (BCA), part of the National Construction Code (NCC), has split Australia into eight climate zones. The Window Energy Rating Scheme has developed a climate zone versus fenestration product guide that can be summarised as:
- Zones 1 to 3 (hot climate) aimed at reducing heat gain
- Zones 4 and 5 (mixed climates) aimed at balancing heat gain versus heat loss, and
- Zones 6 to 8 (cold climates) aimed at reducing heat loss.
It is vital to find true north (also called solar north) for a location to accurately reflect the solar patterns for a building. In all climates, facility managers can use passive solar strategies to their advantage, by either having north-facing windows serve as solar collectors for the building (in cold and mixed climates such as in Melbourne and Sydney) or limiting the solar heat transmission (in hot climates such as Brisbane and Darwin). Best results are achieved if the combination of windows and the building’s thermal mass is matched correctly.
Clever shading and well-designed eaves can admit direct radiation for heating purposes in winter time, yet exclude it in summer, reducing both heating and cooling loads. Northerly windows are useful solar heat collectors in cooler regions in winter, but need eaves or other horizontal shading devices to prevent overheating in summer. This is because, in summer, the sun is very high in the northern sky and the window is easily shaded from direct radiation. In winter, the sun’s lower altitude permits sun penetration through the window. East and west windows are harder to shade because the sun is low in the sky in the morning and afternoon. Horizontal shading devices are of limited use and some form of vertical shading is required such as awning blinds or louvre shutters. In tropical Australia, south-facing windows may need protection by eaves or other horizontal shading systems. This is because, near the Equator, the sun is in the southern sky for much of the day during the summer months.
Using glazing to allow daylight into the building can save energy that would be needed for lighting. The placement of windows and skylights and the amount of reflection from internal surfaces are critical to good day lighting design.
Ventilation is controlled airflow, which can be altered by operable windows. It depends on physical characteristics such as the type of window and the opening size. Windows are a good source of natural ventilation – they help cool the building, increase occupant comfort and reduce energy consumption. In order to provide maximum occupant control, many new windows are now technologically advanced and allow users to operate them using automated mechanisms.
Condensation mainly occurs during colder months when windows are kept closed. The warm air inside increases the level of water vapour in the air. When the warm, moist air hits the cooler window it cools and, unable to hold as much moisture, it deposits the moisture onto the window. This can result in mould development around the edges.
Windows with lower a U-value have interior and exterior glass surfaces that are closer to the adjacent air temperature, reducing condensation.
Ordinary window glass only partially blocks the UV radiation and, as a result, exposure to the lower wavelengths of sunlight can cause interior furnishings to fade. The solution is to select window products that use interlayers such as a laminated glass that will block the majority of UV radiation to penetrate.
How can you ensure that you are getting the performance you are paying for?
The answer is: use products that comply with the AFRC rating.
The AFRC is a not-for-profit organisation that monitors the protocols and procedures used to provide energy rating to all fenestration products in Australia. It comprises and is supported by peak industry associations from the Australian fenestration industry, including the Association of Building Sustainability Assessors, the Australian Glass and Glazing Association, the Australian Window Association, the Insulating Glass Manufacturers Affiliation, the Skylight Industry Association, the Window and Door Industry Council, the Window Film Association of Australia and New Zealand, and the Blind Manufacturers Association of Australia.
Not only is the AFRC supported by industry, it is also required to meet government regulation. The National Construction Code (NCC) requires all window systems to meet the performance requirements for both commercial and residential buildings.
How do I find products that have been rated in accordance with the AFRC?
The AFRC has developed a certified product directory (CPD) on its website, which contains listings of all the products that are energy-rated using the AFRC Protocols and Procedures. Products can be searched by: frame material, manufacturer, window type and glazing type. Alternatively, when discussing your project with the window company, ask if their products have an energy rating.
For more information, check out the AFRC’s Technical Protocols and Procedures Manual for Energy Rating of Fenestration Products.