<Li> Natural ventilation refers to intentionally designed passive methods of introducing subaerial to a space without the use of mechanical systems . </Li> <Li> Mixed mode ventilation (or hybrid ventilation) systems use both natural and mechanical processes . </Li> <Li> Infiltration is the uncontrolled flow of air from outdoors to indoors through leaks (unplanned openings) in a building envelope . When a building design relies on environmentally driven circumstantial infiltration to maintain indoor air quality, this flow has been referred to as adventitious ventilation . </Li> <P> The ventilation rate, for CII buildings, is normally expressed by the volumetric flowrate of subaerial air, introduced to the building . The typical units used are cubic feet per minute (CFM) or liters per second (L / s). The ventilation rate can also be expressed on a per person or per unit floor area basis, such as CFM / p or CFM / ft2, or as air changes per hour (ACH). </P>

What is the purpose of top side vents on a building