Thermal Efficiency - Please select from the headers below:

Westal’s commitment to sustainability is not simply a response to current trends – the company has practiced environmentally sustainable design (ESD) for decades.

Technological advances in the last 25 years have made it possible to design windows which insulate against heat and cold up to four times better than conventional windows.

Energy Efficiency:

An energy-efficient window is one that helps to minimise the use of artificial heating and cooling in a building. In many parts of Australia, the priority is to keep solar heat out of the home, except during colder months, when ‘free' solar heat gain and retention of warmth in the house become important. Heat gain or heat loss take three forms: radiant heat transfer, conductive heat transfer and heat transfer via air infiltration. Ideally, this calls for strong solar protection on east and west windows, but deliberate use of free sunlight (via clear glass) from northerly windows. This means different window solutions for different orientations. Alternatively, it is possible to use the same uniform high-performance window type on all sides of a home - provided it is correctly chosen. From an energy point of view, this is not quite optimal but it simplifies the specification process and still results in very substantial energy savings and improved comfort, compared to using clear single-glazed windows.

In most climates, windows with at least four heating or four cooling stars, on all sides of the house, will ensure that conductive heat losses and heat gains are minimised. This means the windows must have a low U-value. It is possible to reduce the glazing U-value by means of single glazing having a low-e coating. Low-e coatings are near-invisible. While a low-e coating on simple single glazing reduces that part of the heat transfer which is due to radiation, it does nothing to reduce conductive and convective heat flow.

A much better solution is to reduce all three forms of heat transfer. To do this an insulating glass unit (IGU – Double Glazed) is required. The IGU is the vehicle for all high-performance windows, in all climates - hot, cold and mixed. The IGU should preferably have some sort of low-e coating on at least one pane and have argon gas fill between the panes, to give the lowest overall heat transfer. U-values as low as 1.8 are possible, compared with about 5 in the case of a single-glazed clear window. To complement the glazing system, a frame with a low U-value assists in reducing the whole-window U-value.

The most common filling gas between the panes of an IGU is dry air. The narrowest air gap used is 6 mm but this should be avoided unless there is no alternative. The use of wider gaps (10-20 mm) will improve the U-value and increase the WERS heating star rating by at least half a star. The use of argon gas instead of air in the IGU space lifts the heating rating by about a third to half a star in most cases.

Low-e Coatings:

All low-e coatings assist energy efficiency by suppressing radiation heat transfer. This means they act like ‘heat mirrors' and reflect heat back into a room in winter, which reduces the amount lost to the outside. Windows with spectrally selective low-e coatings reduce the solar heat gain coefficient (SHGC) by up to 60% compared with clear 3 mm glass. This reduces or in some cases eliminates the need for wide eaves or shading systems.

Heat leaves or enters a home through gaps and cracks around sashes and frames. When a window is shut it should be “shut”. Traditionally, windows with compression seals, as fitted to awning and casement windows, tended to have superior long-term infiltration performance. However recent advances in some sliding window seals have reduced the gap.

SWA Climate Zones Guides:

SWA - Climate Zones 1, 2 & 3 (2071 KB) 
Northern Australia, Brisbane and Darwin

SWA - Climate Zones 4 & 5 (1937 KB)
Sydney, Perth and Adelaide

SWA - Climate Zones 6, 7 & 8 (1919 KB)
Most of Victoria, ACT, Tasmania and Southern parts of NSW and WA

Information courtesy of the AWA (Australian Window Association)