Glazing in cold climates

Areas included in these climate zones cover most of Victoria, Australian Capital Territory, Tasmania and some Southern parts of New South Wales.

There is no doubting the fact that Australia is the last wealthy nation to take even basic steps to improve the standard of its glazing.

But from May this year, some of that is set to change, in some States at least. And it’s in predominately cold climates like Melbourne’s that some of the greatest energy savings can be made by using better glazing.

Windows will typically represent less than 10 per cent of the surface area of your home, they can quite realistically contribute around 50 per cent of your heat loss in winter.

 Considerations

Maximise opportunity to exploit desirable solar heat gain for majority of year
Reduce heat flowing through windows (in both directions) over course of year

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

“Season-specific” physical shading of windows (e.g. eaves over Northern-facing windows)

Star Impact SHGCw optimised (clear) – offers no improvement in stars (clear is baseline)
U-Value – has the potential to improve up to approximately 0.3 stars for each unit reduction in U-Value. Ventilation – little or no star impact
Heating/Cooling Impact

Each star corresponds to reduction in heating/cooling requirements of approximately 20% to 30% on pre-improved level
In general improved U-Values act to reduce heating load throughout majority of the year, though may marginally increase cooling requirements in periods of hot weather

Cost & GHG Savings Approximately 10,000 to 15,000MJ of energy saved per star, mostly heating – worth about $300/year and approximately 1.0t of GHG. (Based on Melbourne/Hobart, 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.

In a cold climate, over the course of a year we will most often want our homes to be a higher temperature than the air outside – warm homes are inviting and pleasant places to “come home to”.

Cold homes are the opposite.

An appealing and comfortable (and valuable) home would be one that is warm when it’s cold outside. We heat our home with gas heaters and reverse cycle air-conditioning and other energy-consuming devices to keep it comfortable, but so long as it remains cold outside, that heat will make its way to the atmosphere.

It turns out that, compared to wall, roof, and floor materials, glass offers very little resistance to heat flowing through it (think about a café latte served in a glass – it burns your fingers, right?). In fact, there is one common building material that is far more conductive than glass, and that’s aluminium – so the material you chose for the frame of the window has an important role to play also. However, there’s no need to avoid aluminium frames altogether – just make sure that you opt for a thermally improved or thermally broken aluminium frame. Readily available, these types of aluminium frames are specially designed to reduce heat transfer.

The energy loss through ordinary windows is appreciable – on a cool day, a square metre of typical single-glazed glass in a standard aluminium frame can lose energy at a rate equivalent to running an incandescent light bulb. It makes sense to address the “weak link” in the building fabric – those highly conductive windows.

So, a well designed home for a cold climate offers good heat retention within the home – it “keeps its heat” – and low conductivity (low U-value) windows are a critical component of this. For the glass this means Low E glass or IGUs, or ideally a combination of the two.