Glazing In Hot Climates

Hot Climate Zones 1, 2 & 3 - WA, NT, QLDAreas included in these climate zones are Northern Australia, Brisbane and Darwin.

Any mention of windows and hot climates inevitably results in the same statement – “we don’t need to worry about insulating our homes in a hot climate”.

Any time you are investing energy (and cost) into changing the temperature of the air inside your home (heating or cooling), it’s worth considering steps to avoid it becoming uncomfortable in the first place, and keeping it comfortable for as long as possible.

Windows are uniquely powerful in giving us this control.  

Guide to Glass Selection - Climate zones 1, 2 & 3 (heating areas)

Considerations

Keep solar radiation out of the home
Retain coolness of air-conditioned air

Preferred U-Value Low
Preferred SHGCw Low
Other Factors

Windows with high operable areas to maximise opportunity for air movement for natural cooling

Star Impact SHGCw optimised (clear) – has the potential to improve up to approximately 1 star.
U-Value – has the potential to improve up to approximately 0.25 stars for each unit reduction in U-Value.
Ventilation – has the potential to improve up to approximately 0.25 star per additional 20% of openable area.
Heating/Cooling Impact

Each star corresponds to reduction in heating/cooling requirements of 15% to 30% on pre-improved level.
Star uplift due to reducing SHGC reduces cooling load but may marginally increase heating load in cooler months.

  Cost & GHG Savings Approximately 3,000MJ of energy saved per star, mostly cooling – worth about $150-$250/year and up to 0.35t of GHG. (Based on Brisbane, 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 sun is hot – keep it outside.

Direct radiant energy from the sun (i.e. heat ‘shining’ onto your home and through the windows) is hundreds of Watts per square metre. Heat reflected off surfaces and ‘diffused’ radiant heat from particles in the air surrounding your home is also appreciable.

Where present, radiant solar heat is generally the biggest heat load through a window, so it should be the first thing we seek to control. In hot climates, use windows with low SHGC glass, provide adequate physical shading (preferably external devices such as eaves, pergolas, awnings, screens, etc.) to reduce your windows’ exposure to direct sun. Apply this principle to all windows in tropical climates, and in sub-tropical areas focus particularly on the western and northern faces of your building (where the midday and afternoon sun will otherwise overheat an already warm home).

Simple toned glass offers a lower SHGC than ordinary clear float, but it only does half the job. Because simple toned glass absorbs heat which makes the glass itself hot, toned glass will tend to reradiate  heat into your home. You can reduce this significantly by using a low-gain Low E glass (i.e. a low emissivity coated glass with a low SHGC) – the coating reduces the amount of heat radiated off the inner surface of the glass, keeping the inside of your home cooler.