Ventilation (architecture)

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For other uses, see Ventilation.

Ventilation is the intentional movement of air from outside a building to the inside. It is the V in HVAC. With clothes dryers, and combustion equipment such as water heaters, boilers, fireplaces, and woodstoves, their exhausts are often called vents or flues -- this should not be confused with ventilation. Their airflows are exhaust air. Movement of air between indoor spaces, and not the outside, is called transfer air.

Ventilation air, as defined in ASHRAE Standard 62.1<ref>ANSI/ASHRAE Standard 62.1, Ventilation for Acceptable Indoor Air Quality, ASHRAE, Inc., Atlanta, GA, USA</ref> and the ASHRAE Handbook<ref>The ASHRAE Handbook, ASHRAE, Inc., Atlanta, GA, USA</ref>, is that air used for providing acceptable indoor air quality. When people or animals are present in buildings, ventilation air is necessary to dilute and remove airborne pollutants such as respirable suspended particles (RSPs) and volatile organic compounds (VOCs). Ventilation air is often delivered to spaces as part of the supply air which heats, cools, humidifies, and dehumidifies the space. Ventilation air can also be provided via infiltration, natural ventilation, or advanced air filtration and treatment processes such as scrubbing, for example.

In certain applications, such as submarines, pressurized aircraft, and spacecraft, ventilation air is also needed to provide oxygen, and to dilute carbon dioxide for survival. Buildings on Earth have significant air leakage, and rarely have been found to have dangerous O2 or CO2 levels. But inadequate ventilation in a densely-occupied room can cause the level of carbon dioxide to increase leading to sleepiness.

In commercial, industrial, and institutional (CII) buildings, and modern jet aircraft, air is often recirculated. But a percentage of the return air is normally exhausted and replaced by outside air. The rate of ventilation air required, most often provided by this mechanically-induced outside air, is determined from ASHRAE Standard 62.1 for CII buildings, or 62.2 for low-rise residential buildings, or similar standards.

The ventilation rate, for CII buildings, is normally expressed by the volumetric flowrate of outside air being introduced to the building. The typical units used are cubic feet per minute (commonly abbreviated as CFM), or, in metric units, liters per second (L/s). Often, the ventilation rate is expessed on a per person or per unit floor area basis, such as CFM/p or CFM/ft².

For residential buildings, which mostly rely on infiltration for meeting their ventilation needs, the common ventilation rate measure is the number of times the whole interior volume of air is replaced per hour, and is called air changes per hour (I or ACH; units of 1/h). ACHs of 0.5 to 1.5 are common in modern U.S. homes under winter design weather conditions.

If smoking is allowed indoors, of tobacco or other substances, ventilation air is needed in great quantities to dilute the airborne contaminants. However, secondhand smoke exposure, and health risks, cannot be eliminated. Bans of indoor tobacco smoking, candle burning, 'air fresheners', incense, and other generators of air contaminants are much more effective for improving indoor air quality.<ref>Ventilation for Environmental Tobacco Smoke, (c) ASHRAE, Elsevier, Burlington, MA, USA, 2006</ref>

If there is something burning (a fireplace, gas heater, candle, oil lamp, etc.) more oxygen is replaced by carbon dioxide (and possibly other poisonous gases and smoke) and more ventilation air is needed. A chimney causes infiltration or natural ventilation because it moves air from inside to outside. The resulting negative pressure change induced in the building typically causes a flow of air to move into the building replacing the warmer air that leaves by buoyancy through the chimney.

Ventilation in a structure is also needed for removing water vapor, produced by respiration, burning, and cooking, and for removing odors, e.g., from a toilet or kitchen. If water vapor is permitted to accumulate, it may damage the structure, insulation, or finishes. When operating, an air conditioner usually removes excess moisture from the air. A dehumidifier may also be appropriate for removing airborne moisture.

1 Types of ventilation
2 Ventilation equipment
3 Natural ventilation
4 See also
5 References

[edit] Types of ventilation

Mechanical or forced ventilation: as in through an air handling unit or direct injection to a space by a fan. A local exhaust fan can enhance infiltration or natural ventilation, thus increasing the ventilation air flow rate.
Natural ventilation occurs when the air in a space is changed with outdoor air without the use mechanical systems, such as a fan. Most often natural ventilation is assured though operable windows but it can also be achieved through temperature and pressure differences between spaces.
Infiltration is separate from ventilation, but is often used to provide ventilation air

[edit] Ventilation equipment

[edit] Natural ventilation

Natural ventilation is the process of supplying and removing air through an indoor space by natural means. There are two types of natural ventilation occurring in buildings: wind driven ventilation and stack ventilation. The pressures generated by buoyancy, also known as 'the stack effect', are quite low while wind pressures are usually far greater.