Solar Passive Design - How it Works
Core principals
Understanding how the sun moves throughout the day, and year, on your site, is absolutely critical to designing a home that is comfortable and enjoyable, with low energy requirements, all year round. No matter where you are in Australia, the following information applies:
Easterly morning sun and westerly afternoon sun will hit the building at a low angle as the sun rises and sets. Depending on your climate and design, you may want to harness or avoid this short but harsh light and heat.
Because of its low angle, vertical shading, such as blinds, trees or vertical blades, are the most effective form of controlling this light.
As we’re in the southern hemisphere, the sun will predominantly be in the north of the sky during the day. In northern Australia, this is less pronounced and the sun tracks closer to overhead all year round. In southern Australia, the sun is dramatically further north in the sky during winter.
The beauty of this is that in the hotter northern climates, homes can be easily designed to be shaded all year round, while in the south it’s easy to design for summer shading while still capturing the winter sun.
In southern Australia, the south side of the building only receives early morning and late afternoon summer sun. In contrast, up north, the south side of a building is exposed to the sun for much of the day. In other words, southern sun-strike generally occurs at unwanted times.
How to read a sun angle diagram
You can find the sun angle diagram for any location at www.gaisma.com.
Below you can see the angles for Canberra, which has a cool temperate climate that benefits greatly from clever solar passive design.
It shows the path of the sun during the year from a bird’s eye view. The lower dark line shows the path at the summer solstice and the upper dark line represents the winter solstice. The circles radiating from the centre indicate the angle the sun is from the horizon. For example, at noon on the summer solstice, the sun is almost directly overhead, while in winter it is only just over 30º up from the horizon.
A three-dimensional representation of this diagram looks like this:
How to respond to a sun angle diagram
In Canberra’s climate of hot summers and cold winters and with the solar angles shown previously, the following design solution would be appropriate.
This approach works for any cool-temperate and temperate climate in Australia.
To the north of the house, optimised eaves or horizontal shading can maximise winter solar heat gain, while blocking summer sun strike. The offset and projection of the shading device must be considered.
To the east and west, either retractable shading, deciduous planting, or optimised vertical blades or louvres can allow winter sun in, while limiting summer sun.
In summer, the sun strikes southern windows for a shorter period of the day, but does strike them nonetheless, so they should be limited to avoid untimely summer heat gain and winter heat loss. Similar shade solutions as used for the east and west can be applied if required.
Where to find more
The information above is extracted from my book, 101 Things I Didn't Learn in Architecture School; And wish I'd known before my first job.
While the book is written for students and graduates of architecture, it is also an excellent handbook for anyone embarking on their own project. We provide a free copy with every on-site briefing and feasibility meeting, or you can purchase your own copy here.
Another great resource on basic principles in Australia is the YourHome.gov website which is free to access.