Australian Passive Solar Home

As we know, opening the house at night cools the thermal mass. But where does that cooling air come from?

If you said ‘outside’, you’d be right.

But what I have found is that after a hot day, the air entering our house through southern windows is measurably cooler (e.g. 1-2°C) than that entering through northern windows. I assume that this is because the southern side of the house is better shaded than the north, and so the ground is cooler. Therefore, when maximum cooling of thermal mass is needed, it may be worthwhile opening southern windows first.

Certainly, being able to source night cooling air from the south is important, so keep this in mind when planning your house – you need ventilation openings on this side.

The fact that the southern air is cooler for night flush cooling also opens another possibility that we may employ in our house. That is, when nights are warm, to draw the night flush cooling air through spray-irrigated bushes outside the southern windows, evaporatively cooling to this air.