There are multiple techniques for natural ventilation and cooling in buildings.

Thermal Chimneys and Evaporative Cooling

In hot, dry climates, thermal chimneys and evaporative cooling are effective and have been used for thousands of years in the Middle East.

A thermal chimney uses solar energy to heat air, which rises and is exhausted out the top of the chimney, causing a natural convection loop as cooler air is drawn into the building (sometimes through a cool underground duct) to replace the exhausted hot air.

Evaporative cooling draws heat from the air to vaporize water, making the resultant air cooler and more humid. This works in dry climates, where it may be desirable to add humidity.

Thermal Mass Cooling

Earth sheltering and earth coupling take advantage of the vast thermal mass of the ground, which remains a constant temperature at a certain depth below grade (the depth depending on the climate). Earth sheltering can also protect the building from inclement weather, such as strong wind.

In a climate with a large diurnal temperature swing, thermal mass cooling can be accomplished by allowing cool nighttime air to flow across a large indoor building mass, such as a slab. The cool thermal mass then absorbs heat during the day.

Radiant Cooling

Though not a passive technology, radiant cooling is more efficient than conventional systems that circulate conditioned air. Typically, radiant cooling involves running cool water through floor slabs, or wall or ceiling panels.

In a hot dry climate, the water can be cooled evaporatively and radiatively by spraying it over a building roof at night, then collecting and storing the cooled water for use the next day.

In a humid climate, dehumidification is needed in addition to cooling, but lowering humidity and providing airflow can enable people to be comfortable at temperatures up to nine degrees warmer than they otherwise would be.

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