Ventilation

The deliberate movement of air from the outside of a building to its inside quarters is called ventilation. It is what the letter "V" in HVAC stands for. Where clothes dryers and certain combustion equipment are concerned (such as boilers, fireplaces, water heaters, and wood stoves), their exhaust mechanisms are referred to as flues or vents. So as not to bring harm to the occupants of a building, these flues or vents carry combustible products out from the structure. When air is intentionally moved within the inside quarters of a building, this is referred to as transfer air.

Ventilation air is defined as that type of air used to provide quality indoor air to the occupants of a building. When animals and people are within the confines of a building, ventilation air is required for the following reasons:

&bull dilution of odors

&bull limiting the concentration of carbon dioxide

&bull limiting the concentration of respirable suspended particles (RSP's)

&bull limiting the concentration of volatile organic compounds (VOC's)

Characteristically, the movement of ventilation air is done by certain mechanical systems such as those that either cool, de-humidify, heat, or humidify the space. Air movement into a building can occur due to uncontrolled infiltration of outside air through the building's fabric (a.k.a. the Stack Effect) or by virtue of deliberate natural ventilation. There are also advanced air filtration and treatment processes that are referred to as scrubbing. This is a process where ventilation air is created by the cleaning and then the recirculation of portions of the air already inside the building.

There are certain applications wherein ventilation air is required to provide oxygen and dilute carbon dioxide for survival purposes. These applications would be:

&bull pressurized aircraft

&bull spacecraft

&bull submarines

Dangerous levels of carbon dioxide within buildings are also prevented by virtue of the structure's natural air leakage. In densely populated buildings, improper or inadequate ventilation can result in employee sleepiness and a reduction in the work efficiency levels because the levels of carbon dioxide have increased. Where attentiveness and learning abilities in schools becomes adversely affected, it is normally due to poor or substandard ventilation of the classrooms.

Air changes per hour (ACH) is the common ventilation rate measurement used within residential buildings to gauge the number of times the whole interior volume of air is replaced every hour and relates to the use of infiltration to scrub the air. In commercial buildings, this measurement is normally measured by virtue of the volumetric flowrate of outside air that gets introduced into the building. The two most common measurements are CFM (cubic feet per minute) and L/s (liters per second). Per person or per unit of floor area is also two other ways that the measurements can be performed.

Where smoking is allowed indoors, sufficient quantities of ventilation air is required in order to dilute and reduce the number of airborne contaminants. In an effort to improve indoor air quality, certain states in the United States and various countries have banned the use of the following within public buildings:

&bull air fresheners

&bull candles

&bull incense

&bull smoking tobacco

• Ventilation
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