Glazing In Mixed Climates

Mixed Climate Zones 4 & 5 - NSW, WA, SA

Areas included in these climate zones are Sydney, Perth and Adelaide.

In mixed climates you need to account for hot and cool conditions in roughly equal energy proportions over the course of the year. You ask the same set of windows to keep the inside conditions cool in summer, yet warm in winter.

Measures that work for a hot or cold climate may work in a mixed climate for part of the year, but they can increase the heating and cooling load on the home at other times of the year.

Guide to Glass Selection - Climate zones 4 & 5 (mixed areas)

 Considerations

Balance the benefits of solar heat gain in winter against keeping cool in summer.
Use mid-range solar control
Reduce heat flowing through windows (in & out) over course of year

 Preferred U-Value Low
 Preferred SHGCw Mid Range (or ideally tuned by elevation)
 Other Factors

“Season-specific” physical shading of windows (e.g. eaves over Northern-facing windows)
Windows with adequate openable area for ventilationar

Star Impact SHGCw optimised (clear to toned) – approximately 0 to 0.5 stars
U-Value – approximately 0.33 stars for each unit reduction in U-Value
Ventilation – little impact beyond the average of 20% openable area
Heating/Cooling Impact

Each star corresponds to reduction in heating/cooling requirements of approximately 20% to 30% on pre-improved level
Star uplift due to reducing SHGCw reduces cooling load but may increase heating load in cooler months
In general U-Value improvements act to reduce heat and cooling loads

Cost & GHG Savings Approximately 3,000MJ of energy saved per star, mostly cooling – worth about $250/year and up to 0.4t of GHG. (Based on Sydney/Perth/Adelaide, 240m2 house)

 

Notes:
1. This information is a guide only.
2. For more specific information refer to your window or glass supplier or the WERS Website (www.wers.net)
3. For window selection, Australian Building Code requirements and energy raters will specify actual U-Values and SHGCw for BCA-DTS or simulation tools such as AccuRate, FirstRate 5 or BERS Pro.

The easiest answer (and the one used in the SWA modeling) is to use the same glazing throughout – it’s simple, fool-proof, and overcomes issues of variances in design or orientation. In this case we should choose a product with a mid-range SHGC, one which compromises between summer and winter, a window SHGC of 0.3 to 0.5.

Though we’ll miss out on a bit of desirable passive heating in winter, we’ll make it back in the savings on cooling over summer. But we can do better – we can exploit the

very predictable path of the sun (day to night and through the seasons) and use physical shading to shield our windows when we want to keep cool, and leave our windows unobstructed at colder times. This doesn't mean closing a blind or the curtains – if we’re clever we can avoid (or certainly reduce) the need to take any manual action to block out the light and view in order to control heat.

So the daily path of the sun is familiar enough – rises in the east, sets in the west. Typically night-time temperatures will be cooler than the following day, so we’re happy to bring warmth into the home in the morning, but less pleased with inviting heat in during the afternoon (potentially overheating an already warm house).

In terms of glazing, we’d consider using lower SHGC windows on the west than elsewhere in the home. The east may also warrant some solar control, but usually not to the same extreme as the west.