Peter Simmonds
Building and Systems Analytics, LLC, Los Angeles

The term “natural ventilation” has been in use at least since 1899, when a 21-page pamphlet called “Natural Ventilation” was reprinted from an article in The Building News, and later a 92-page compendium of the prevailing arguments of the day entitled “Natural and Artificial Methods of Ventilation.” The challenge at the time was to establish how to design “engineered” natural ventilation systems to give equivalent ventilation performance, as one might achieve with mechanical systems. This remains the challenge we attempt to tackle over a century later.

Ventilation is the provision of outside air to a space. When people talk about natural ventilation in normal parlance, they usually envisage opening a window to bring fresh air into a space. The adjective “natural” is used to differentiate the driving force causing the air movement, as compared to a “mechanical” means. Though obvious, the following basic natural ventilation principles bear repeating. Firstly, natural ventilation only works if there are at least two openings (or a very tall opening that acts as a two-way opening). Second, the amount of airflow is controlled by the size of the smallest opening. Third, air will always follow the path of least resistance.

We know that the outside climate changes over the height of a tall building. So how does this affect the utilization of natural ventilation? How is natural ventilation calculated? And how do we address occupant comfort?