Natural ventilation is a climate control method which relies on the natural movements of air to keep fresh air moving through a building and to control temperature and humidity levels. While this was the only ventilation option available historically, once mechanical means of ventilation were developed, many builders switched to these methods. In the late 20th century, some of the distinct advantages of natural ventilation began to be recognized, and builders started returning to the use of natural techniques.
There are several ways to create natural ventilation in the structure. One of the most basic is probably also one of the most familiar: create windows which open to generate wind driven ventilation. By opening and closing windows, people can control the flow of air through a structure, opening more windows to encourage fresh air, which can cool a structure in addition to carrying away odors, and closing windows to generate less of a flow of air, keeping a structure warmer and sometimes increasing humidity.
Stack ventilation is another natural ventilation option. With stack ventilation, people rely on natural pressure differences between air in various locations to force air up ventilation stacks. This technique is often used in factories, where tremendous amounts of heat can be generated, with the air being pulled up the stacks along with odors from the factory floor. Stack ventilation is usually facilitated with the use of intake vents which are located low to the ground, generating a steady flow of fresh, cool air.
One of the biggest advantages of natural ventilation is that it does not cost any money to run. Mechanical ventilation and electronic climate control can be quite costly, and may contribute significantly to the overall energy costs involved with running a building. No use of energy also makes this type of ventilation an environmentally friendly choice. Such systems tend to be easier to maintain, as well, with no parts to break or go wrong, they can't disturb occupants of the building with interruptions in ventilation or add to the operating costs for the ventilation system.
For many private homes, efficient building combined with natural ventilation is enough to satisfy ventilation needs. Larger structures may require a blend of natural and mechanical ventilation to keep air quality at a reasonable level. Green buildings are often specifically designed to rely primarily on natural ventilation for energy efficiency reasons, and it is also possible to retrofit buildings to accommodate natural ventilation, for people who are interested in making structures more energy efficient.