This technique is used both for passive cooling as well as heating of buildings, a feat which is made possible by the earth acting as a massive heat sink. Summer as well as winter variations die out rapidly with increasing depth from the earth's surface. This temperature at a depth of a few meters remains almost stable throughout the year. Thus, the underground or partially sunk buildings would provide both cooling (in the summer) and heating (in the winter) to the living space. Besides, load fluctuations are reduced by the addition of earth mass to the thermal mass of the building. The infiltration of air from outside is reduced.
The earth sheltered structure has to be heavier and stronger to withstand the load of the earth and the vegetation above. Besides, it should be suitably waterproofed and insulated to avoid ground moisture.
Additional heating, if required, can be provided by means of direct gain through windows near the roof projecting above the ground. Similarly, additional cooling if required can be provided by circulating air through ducts built underground (where the temperature is low). The same ducts can provide some degree of preheating for the fresh outside air during the cold periods.