Ventilation

It is the process by which ‘clean’ air (normally outdoor air) is intentionally provided to a space and stale air is removed. This may be accomplished by either natural or mechanical means.

Indoor air quality (IAQ)
It is a growing concern today. Concern with energy conservation has made building construction nearly airtight, which, in turn, has made proper ventilation more important than ever. People today are spending the majority of their lives indoors, more than 90% of the time according to the EPA (United States Environmental Protection Agency).Managing indoor air quality can have a big impact on the satisfaction, productivity and health of occupants.

Three general categories of contaminants can impact IAQ:
Biological, Chemical and Particle related pollutants

Outdoor Air Quality
An issue that is frequently overlooked and ends up being dealt with after the fact is the impact of the surrounding environment on a building. Too often, aesthetic consideration places outdoor air intakes in areas of the building that may be exposed to all sorts of problems. The quality of the indoor air will be affected if an intake is facing heavy traffic, industrial discharges, or other sources of unwanted pollutants. Such situations may require special filtration, could lead to premature loading of filters, increased maintenance and cleaning costs and unexpected wear and tear on the equipment.

Ventilation refers to the amount of fresh air supplied throughout the building. In the interest of energy conservation, air is typically recirculated and mixed with some amount of fresh air at the air handler. Introducing fresh air helps dilute any airborne contamination and exhausts it out of the building faster. According to industry studies, over half of the indoor air quality complaints reported can be traced to problems in ventilation. ASHRAE Standard 62 offers detailed recommendations pertaining to ventilation in occupied spaces.

Assessment should be done on a regular basis. In climates with wide shifts in weather conditions, this analysis should be done at a minimum when the system is being changed over from heating to cooling and vice versa. Ventilation should always be checked whenever an occupant complaint triggers an investigation and when changes or modifications are made to the HVAC system or to physical characteristics of a building.

Measurements need to be made in all occupied spaces within a building. It is important to remember that in buildings with multiple air handling systems each system must be evaluated separately, almost like another building

A good indicator of proper ventilation in a space is the level of CO2, a natural by-product of respiration, combustion and other processes. Elevated levels of carbon dioxide can be an indication that additional ventilation or outdoor air may be needed. ASHRAE Standard 62 recommends that indoor levels not exceed roughly 700 ppm more than outside ambient conditions. Higher levels of CO2 may cause slight drowsiness, enhance odors or give the impression of stale air.Reducing CO2 levels in an occupied space is accomplished by increasing the number of air exchanges and/or percentage of outdoor air supplied to the conditioned space.

To ensure that a building is properly ventilated, it is important to take CO2 measurements in occupied areas, air distribution zones, at varying heights and compare them to the outdoor level. To get accurate data on CO2 levels in an occupied space, data should be logged over a period of time so any fluctuations can be analyzed. CO2 levels will naturally fluctuate during the work day based on occupancy and facility usage. During the evening hours, when the building is unoccupied, CO2 levels generally drop. As the day begins and workers arrive, CO2 levels will tend to rise.

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