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Simply put, ventilation is a system that provides fresh air. There are two types of ventilation: mechanical (provided by a heating or air conditioning system) or natural (coming directly from the outdoors).Ventilation moves outdoor air into a building to remove pollutants and provide acceptable indoor air quality (IAQ). Ventilation air (fresh outdoor air) is not exactly the same as the supply air coming out of an air diffuser (or other supply vent). Supply air typically is a mixture of outdoor and recirculated air. Many large buildings have integrated heating, ventilating, and air-conditioning (HVAC) systems. However, the units that heat, cool and humidify or dehumidify indoor spaces do not deliver ventilation air unless there is a source of outdoor air intake.

Ventilation can impact indoor air quality and health

Ventilation is an important control strategy for maintaining good indoor air quality (IAQ) and improving poor IAQ. Properly designed ventilation can dilute particles and gases in indoor air and prevent contaminants from accumulating to levels that may cause health or comfort problems. It can also remove excessive moisture and prevent microbial growth.

Ventilation should be used in conjunction with source control (preventing contaminants from entering the air) and, in some cases, air cleaning (see Summary of Available Information on Residential Air Cleaners from US Environmental Protection Agency ). In general, it is more efficient to eliminate or reduce sources of indoor pollutants or use local exhaust ventilation or air cleaning devices to remove them near their source than to control them by general ventilation.
Ventilation rates that are too low can cause pollutants and moisture to build up to levels that may lead to unpleasant odors, discomfort, or even adverse health effects. Lower ventilation rates have been associated with higher symptom rates and reduced performance in school or work settings. Therefore, higher ventilation rates are generally desirable from the IAQ point of view. However, there are two reasons not to provide exceedingly high ventilation levels:
1) Increasing the ventilation rate may increase energy consumption if the outdoor or recirculated air must be ?conditioned,? that is, cooled or heated and perhaps dehumidified or humidified.
2) If a contaminant is present at higher levels in the outdoor air that is brought into a building (for example, ozone or pollutants exhausted from vehicles), then increasing the ventilation rate may bring in pollutants more harmful than those that are being removed, unless the air coming in is treated to remove the contaminants from outdoors.

In practice, building ventilation rates need to balance energy consumption with the known or expected health and comfort benefits. More information regarding the effect of ventilation rate on IAQ, health, and productivity can be found at the website of Lawrence Berkeley National Laboratory?s Indoor Environment Department (see Ventilation Rates and Technologies).

Ventilation Codes

Standards and codes establish minimum ventilation rates to provide comfortable indoor environments and protect human health.1 The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) recommends minimum ventilation rates for different types of buildings and spaces (see ASHRAE Std 62.1-2007 and ASHRAE Std 62.2-2007), which are often incorporated into national, state, and local codes. Typically standards and codes specify the minimum ventilation rate ?per person? or ?per unit of floor area? (square meter, m2, or square foot, ft2). The minimum varies with the type of building or usage of the space, for example, a higher air change rate is recommended for health club weight rooms (26 cfm/person based on default occupant density) than for office spaces (17 cfm/person) because the higher activity levels in the weight room will produce more occupant-related odors. The Code of Regulations identifies the minimum ventilation rates required for California buildings (see California's Energy Efficiency Standards for Residential and Nonresidential Buildings).

California workers are fortunate in that not only must workplace mechanical ventilation systems be designed and built to meet code requirements, the systems also must: (i) be operated to provide at least the quantity of outdoor air required by code, (ii) be operated continuously during working hours (with exceptions), (iii) be inspected at least annually and problems corrected within a reasonable time, (iv) be maintained, and (v) records of all system inspections and maintenance be kept in writing and available within 48 hours of request (see the Cal/OSHA Minimum Ventilation Standard).

Last modified on: 4/19/2014 10:44 AM