A common misconception about Passive House is that you can’t utilise natural ventilation.
Nothing could be further from the truth.
Passivhaus is a comfort standard that seeks to maintain optimum internal comfort levels with minimum energy use. So if the external temperatures are amenable, open your windows! Let that breeze through your house and enjoy the indoor / outdoor lifestyle that Perth is famous for.
The main difference with a Passivhaus is that you don’t need to rely on natural ventilation to be comfortable. If the windows are closed you can still enjoy a constant supply of fresh filtered air delivered at the a comfortable temperature and humidity level.
There is also the perception that Perth has a favourable climate for most of they year. However looking at average daily maximum temperatures, only 4 months of the year have conditions within the comfort range of 21 to 24 degrees (April, May, Oct, Nov). Even during these months early morning temperatures can be cold, down to 10 degrees, and this wouldn’t be welcome when you wake up first thing in the morning. Similarly, these months can experience very hot weather - up to 37 degrees plus.
During these peak and low temperature periods it is best to stabilise the internal environment by keeping the doors and windows closed and allowing the ventilation system to do its job, but if you want to open your windows go ahead, do what makes you feel most comfortable!