Persian wind towers, badgirs, are passive building cooling systems that use nature to provide comfort for people in hot anddry regions. They collect fresh air and channel it down to cool the internal spaces. Sometimes they perform as ventilators and conduct the air from the ground level courtyard to the top of the wind tower.
In this paper, the construction techniques of wind towers along with the typology are studied. The typology is based on the location, the number of  inlets, the cooling performance, and the seismic behaviour of badgirs.
The wind towers in Kashan, Central Iran, are studied for their cooling functioning and structural behaviour against earthquakes. Four different heights for the towers are considered. The effects of wind tower height, wind orientation and velocity on mass flow and are examined.
The wind towers may be categorised based on different criteria including  the location, the number of air inlets, the plan, and the facade. Sometimes, they take their names from the city in which they are built.
A wind tower is made of adobe or brick, in the shape of a canal that conducts wind from the top to the bottom. Construction of a wind tower consists of three phases. In the first phase, the lower part is constructed from the basement of the building up to the roof level. In the second phase, the upper part of is built on the roof. The third phaseconsists of building the roof of the badgir with wooden boards and cob, and a gutter is inserted to conduct rainwater.
The number of air inlets and the orientation of badgirs are selected with reference to the direction of the dominant wind, location and geographical conditions. The number of inlets or sides on the top of the wind tower may vary from one to eight. In cities near the desert, the direction of sandstorms play a role in determining which sides on the top of the tower will be closed to prevent the sand from penetrating the living quarters.
A badgir may function as a ventilator when wind does not blow or wind direction is 90°, i.e. mass flow is negative and airflow is from the bottom to the top of the wind tower. In cases where the wind tower performs as a ventilator, the cool air of the courtyard or basement is used for cooling the building.
Wind direction,velocity, and height of a wind tower affect mass flow and temperature. The wind direction of 45° causes more mass flow than other directions; in some cases the difference may be as great as 43% . A taller wind tower increases the air temperature and decreases the mass flow entering from the wind tower to the building. Air temperature increase is less than 0.5 °C. Mass flow decrease is more than 13% for increasing the wind tower height from 4 m to 10 m. A larger velocity of wind decreases the air temperature and increases the mass flow. Increasing wind velocity from 7.5 m/s to 15 m/s causes a 65% increase in mass flow. Wind towers are vulnerable against earthquakes. Taller wind towers experience more damage due to earthquakes than lower ones