Green architecture – but what about hot still days?

Melted Ice Cream Truck_2We can go a long way to achieving thermal comfort without the need for airconditioning in most of Australia. All our Australian offices are mixed mode, in our Sydney office we have made it through the hottest summer in Australian history and only turned on our air conditioning for on for 6 days!

We achieve a good level of comfort on hot days when we have a good breeze blowing and can design to capture these breezes. The question I then get asked every time we design or propose natural ventilation is – “but what about hot still days, when the wind isn’t blowing?”

Well here is the answer.

Weather Nerding 

The Bureau of Meteorology is a big friend of a weather nerd like me. They record weather data at over a hundred weather stations across Australia, many of them have hourly data going back to the early 70’s with daily data going back to the 1800’s.

For a very reasonable fee you can buy a lot of weather data – which is awesome (for me).

At Cundall we use this data to inform masterplanning, subdivision layouts, optimise orientation and debunk myths.

Do we get hot and still days

The answer to the question of hot still days can be answered with weather data for most locations across Australia.

Lets take Sydney as one example.

Using hourly weather data we can analyse for each temperature band what the coincident wind conditions were. We then count the wind speeds and the number of occurrences.

The table below shows the average number of hours per year for each temperature band for each wind speed, together with the percentage of each temperature occurrences that have no wind – still days.


I originally hail from England where I used to think that 27degC was a heat wave, I now know that’s a nice spring day!

So in Sydney, I would class above 30degC as a hot day.

The average number of annual hours where the temperature has been over 30degC AND there has been no wind movement, over the 10 years from 2000 to 2010 – Zero.

Do we get hot still days in Sydney – maybe a couple of hours over a 10 year period, but basically no we don’t get hot still days.

Any weather nerd questions you would like to ask, please drop me a comment below.

2 Comments on “Green architecture – but what about hot still days?”

  1. “All our Australian offices are mixed-mode”… except for the Perth office which is 100% natural ventilation!

    Nice article Simon, I find myself always explaining to clients the number of very hot days, even in Perth, is typically about 5-10 per year (This summer was the hottest on record and we had 3 heat waves which caused the max temperatures reached above 37 for a total of 15 days). Of course on those days it feels like the world is going, to end and everyone remembers them… but for the remaining 270 working days of the year the conditions are absolutely perfect… and on those days we all agree that the few days of discomfort are more than compensated by the almost thermally perfect comfort conditions that comes with good natural ventilation.

    Clients who have spend many years of their lives working in glass boxes with suit jackets on in the middle of winter because its too cold have a hard time relating to how good natural ventilation can actually be.

    • Thanks Mark, I forgot the extra commitment you guys make. When we relocate to different countries or cities with different climates it takes about 6 months for our psychological expectations of thermal comfort to change. This is exactly the same going from an air conditioned office to a naturally ventilated office – give it six months and people will adjust and probably prefer the new environment.

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