@Determined, whenever we actually get to fixing up our place, we want to make it as "climate change proof" as we can manage. That means trying to keep it a comfortable temperature with as little additional heating and cooling as possible. Weather is likely to become more extreme, and already the state power grid is failing in prolonged heatwaves. So I've spent ages researching insulation, heat gain and loss, air circulation...
The basic rule is that if you want to heat or cool a place, you create an insulated shell with minimal air exchange and heat or cool within that shell. However, minimal air exchange can become unhealthy, so the trick there is to find ways of venting air in that's already been cooled or warmed to some degree, and selectively venting out hot air in summer. (Because cold air sinks, venting out cold air in winter doesn't work...)
A ceiling level vent opened during summer gives the rising hot air an escape point, and if you have a vent somewhere low down and permantly shaded, cool air gets drawn in to replace the vented hot air. We've got a very shady corner on the south wall that gets no direct summer sun at all, so that's our prime cool air vent position (some day). Our old fashioned roof cavity has about 7' headspace along the hipline, so if we built an insulated false ceiling about 1' down and replaced about 1 1/2' of the corrugated iron with black colourbond, that would create a "vent space" that would get really warm in summer. The hot air escaping from that via either a louvered vent at the end of it or a couple of whirlys would create an updraft that could be used to draw warm air out of the house and therefore cool air in, via a similar system of ceiling vents and ducting...
And there's ways and means in winter too of bringing solar heated fresh air in... but that's another story. 😛
