Australian Passive Solar Home

A key reason that a passive solar home feels so cool in summer is because you’re exposed to cool surrounding surfaces. Wherever you are in the house, you’re near the cool floor slab; and in some rooms of our house, you’re also exposed to a cool brick feature wall and/or a metal tank of cool water.

The pic shows a measured inside air temperature of 22.8 deg C – pretty good when outside it’s 38 deg C. (No air conditioning.)

But the *radiant* temperature is even cooler – it’s 22.2 deg C. That 0.8 deg C lower temperature is easily able to be felt, especially if you have bare arms and legs (and who would have them covered if it’s 38 outside?).

This radiant heat transfer to cooler surrounding surfaces is one reason that people, when they enter our house on a hot day, always exclaim, “But it feels so cool!”

Importantly, this effect does not occur in homes that lack internal thermal mass. In those homes, all the surrounding surfaces are the same temperature (or even higher) than internal air temperature – so without the flow of air from an air conditioner, you feel hotter than the air temperature, not cooler.