WERS is an energy rating scheme that has been implemented by the Australian Window Association with the support of the Australian Greenhouse Office. WERS rates the energy impact of residential windows and doors with a variety of glass options. AWS or Vantage windows and doors which we manufacture have been WERS rated. Thermal performance software for accessing the energy rating of the building envelope (including windows and doors) is now in use in most states and operating under a variety of names. BERS governs Queensland, Basix covering NSW and ACT with First Rate covering Victoria, South Australia and Tasmania.
The important performance indicators are U-Value (Uw) and Solar Heat Gain Coefficient (SHGC). The U-Value is the measure of air to air transfer through the window due to the thermal conductance of the window frame and glass and the difference between indoor and outdoor temperatures. By comparing the U-Values it is possible to determine the relative thermal insulation performance of the window and glass types. The lower the U-Value of the window system, the lower the heat transference between outside and inside, therefore the better the insulation properties of the window system. SHGC is a measure of total solar energy transmittance entering a building through a window and door as heat gain. The lower the SHGC the better the window and door controls the heat energy transmission.
Glazing, which forms a major content of a window, is approximately 8% of the total house envelope but is responsible for approximately 49% of a homes heat loss and around 87% of its heat gain.
The decision in glass selection is usually one of balance between light, heat and fading.
How much light and heat do you wish to enter into a room, and how much fading occurs as a result. Most people wish to reduce the heat-gain in summer and reduce the heat-loss in winter. Tinted glass reduces the amount of heat and light from the sun that enters your home. The common colours are grey, bronze, green and blue. It provides better heat and UV protection than clear glass and doesn’t have the mirror-like appearance of reflective glass. Reflective glass looks rather like mirror glass when viewed from the outside. It’s particularly effective in cutting down solar heat gain and is useful in large areas of glass facing west and especially in overhead glazing.
Double-glazing (Insulated glass units) will provide considerable performance gains over the single glazing option, but at an increased cost. In summer it reduces heat and UV entry while in winter it provides good light entry and reduces outward heat loss.
The economic option is to use a single pane of solar control glass like Low-E (low-emissivity glass is specially designed to reduce heat transfer in warmer and colder climates). Low-E glass works most efficiently in insulated glass units.