Ventilation primarily takes two forms – natural and mechanical. Natural ventilation is the process of fresh air entering a building via a window, door or other opening while mechanical ventilation is air that is drawn into the building using machinery (typically fans).
Good ventilation is essential to human well being, the provision of fresh air in replacement of stale air maintains the correct levels of oxygen and carbon dioxide in the air, and removes odours, bacteria, excess heat and other atmospheric contaminants. It also prevents condensation, which is caused by excess humidity. The capability of a ventilation system for an individual room is usually measured according to how many ‘changes of air’ it is capable of per hour, that is how many times all the air in the room can be completely replaced. The amount of ventilation required varies considerably depending on what the space is used for; an office will typically need far fewer changes of air than a kitchen or factory.
Pros and cons
Natural ventilation systems have many advantages over mechanical ones. The most obvious is perhaps that mechanical systems use a considerable amount of electricity while natural ones are effectively ‘free’. There are also considerable capital costs in installing mechanical systems. Many people prefer opening a window to having forced air and natural systems are easier to control locally, i.e. by opening or closing a window as required. On the other hand, mechanical systems have distinct advantages over natural systems as well. Natural ventilation is generally not effective in buildings with a large floor plan and opening windows to get fresh air while heating systems are operational wastes energy. Air brought in via mechanical systems can be heated or cooled and the humidity can also be controlled. This can avoid the need for separate heaters or air conditioners. Mechanically drafted air is also generally filtered so is arguably purer than natural air.