Air Flow Coefficient
Air flow coefficients are used in the calculation of air infiltration rates through cracks and gaps as well as ventilation through apertures, vents and ducts. Their value is dependent on the size and shape of openings as well at any bends, edges and other impedances within the air flow path.
Air Infiltration
Air infiltration is basically the uncontrolled leakage of air through openings, cracks and gaps within the external fabric of a building. It is significantly affected by wind pressures and temperature differences between the inside and outside of a building or construction. Infiltration differs from ventilation in that it is uncontrolled, typically unintentional and varies significantly with changing weather conditions.
Air Porosity
Not all materials are completely impermeable to air. Many materials contain small holes and voids within them that air can enter into and potentially flow through. Air porosity is a measure of the volume of these voids given as a ratio to the volume of the outer extents of the material.