NetZeroCities

Natural ventilation (or passive ventilation) makes use of natural forces, such as wind and thermal buoyancy, to circulate air to and from an indoor space in order to maintain good air quality. These ventilation systems work to regulate the internal air temperature as well as bring fresh air in and send state air out. This is largely achieved through the opening and closing of windows and vents which act as a source of air as well as exhaust.

Natural ventilation: single-sided ventilation, cross ventilation and stack ventilation. Source: https://www.windowmaster.com/

Natural ventilation strategies depend on the design of the building, internal thermal loads, and the positioning of openings (typically windows). Natural ventilation can be single-sided ventilation, cross ventilation or stack ventilation, depending on the building's characteristics.

Additionally, for natural ventilation it can be used also windcatchers (traditional in Persian architecture), which generally have the form of small towers installed on top of buildings and draw air from outside into a building, providing natural ventialtion in hot, arid and humid areas.

Windcatcher (for natural ventilation). Source: https://www.wikiwand.com/en/Windcatcher

Climate and geography:

External conditions such as temperature, relative humidity and air quality will affect the potential for implementing natural ventilation in buildings. This generally means that extreme climates with high external air temperature and relative humidity have a lower potential to design with natural ventilation. The role that building design plays in the potential for natural ventilation, whether for new or existing building, is also essential. In temperate climates (as in Denmark, Norway, Germany, Switzerland, and most of the UK), the natural ventilation works quite well.… In climates with higher external temperatures or relative humidity, mixed mode ventilation (or hybrid ventilation) is an effective approach to get the best benefits of natural ventilation without compromising indoor air quality. In this mixed mode ventilation approach, the natural ventilation can be switched on or off depending on the outdoor conditions. This helps to ensure that the building performance requirements are met for both optimal comfort and energy savings. With respect to the windcatchers, they have limited application in regions with very low wind speed.

Urban form and layout:

External elements such as trees, adjacent buildings or other structures need to be considered since they may obstruct the wind.

Technical aspects/ infrastructure:

Almost all buildings can make use of passive ventilation, especially office buildings, schools, theatres and hospitals. Buildings should be oriented so that the windward wall is perpendicular to the summer wind (check out the wind rose map to determine the local prevailing wind direction). Thus, passive ventilation is easier to implement in new constructions, but it is also possible to integrate it in existing buildings, and to combine it with other systems already in place. The new passive system will complement the existing one to take advantage of the use of natural forces.

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