As we have seen in the "Thermal Stability" section, the Earth Sheltered House derives it's inside stable air temperature from the surrounding Earth in direct contact the exterior walls, and that the sub-surface temperature is equal to the average annual air temperature directly above.
Most places in Australia have average annual air temperatures between 14 and 19 degrees Celsius, which is within the human comfort level, so using the ground temperature as a continuous heat source makes sense.
However....Parts of Europe and North Americahave average annual air temperatures far lower than we do in Australia, some being near or below zero, so their earth sheltered houses are completely different to ours in Australia. They don't use the stable ground temperature, but instead they isolate themselves from it with large amounts of foam insulation on the outside and use the structure as thermal mass to retain all the heat energy they have to put into the house for most of the year...luckily their power costs are lower that ours!
Australian Earth Sheltered Houses use the Earth as their primary source of thermal mass . . . . . not the house structure. Aren't you glad you live in a country where the climate is so good!
Each Australian climatic zones needs a particular approach when designing an Earth Sheltered House. Tropical houses obviously need more air movement than those in temperate zones.
The micro-climate of a site can play a very big part in the initial design phase and needs to be fully understood.