Most of us work in environments with some type of Heating, Ventilation and Air-Conditioning system (HVAC). HVACs are designed to maintain comfortable temperature and humidity levels and filter out any harmful air pollutants. Ventilation is defined as the supply and removal of air from inside a building. This process typically includes bringing in outdoor air, conditioning and mixing it with some of the indoor air and exhausting some of the indoor air outside. The quality of indoor air may deteriorate when this process is not working properly.

Sick Building Syndrome (SBS)

HVAC systems that are improperly operated or maintained can also contribute to Sick Building Syndrome (SBS). Some of the symptoms of SBS include dry mucous membranes and eye, nose, and throat irritation. These disorders lead to increased employee sick days and reduced work efficiency. The National Institute for Occupational Safety and Health reports that poor ventilation is an important contributing factor in many sick building cases.

ASHRAE Standards 62-1989 & 62-2001

In 1989, the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) published its "Standard 62-1989: Ventilation for Acceptable Indoor Air Quality". This standard applies to all types of facilities and recommends a range of 15 to 60 cfm/person, depending upon the activity in that room. Because of recent IAQ litigation, many HVAC system designers view ASHRAE Standard 62-89, as a minimum ventilation standard that must be met, in addition to local codes. In 2001 ASHRAE reviewed Standard 62-1989, approved and transferred to Standard 62-2001.

Ventilation System Problems and Solutions

The processes involved in ventilation provide for the filtering of pollutants. Increasing the rate at which outdoor air is supplied into the building increases indoor air quality. Buildings with high ventilation rates may suffer indoor air problems due to an uneven distribution of air, or inadequate exhaust ventilation. Well-ventilated buildings may also have a strong pollutant source, which will impair the indoor air quality. The closer such a source is to an exhaust the more effective the ventilation. It is good practice to provide separate exhaust systems in areas where copy machines or solvents are used. Providing exhaust for these specific sources can result in a reduction of the overall building exhaust ventilation needed.

System Design

• Designs that specify HVAC system operation at reduced or interrupted flow during certain parts of the day can cause increased indoor contaminant levels and impair removal. Minimum ventilation rates should be defined by air cleanliness and distribution, as well as temperature and humidity.
• Failure to maintain proper temperature, humidity and air movement in a building can lead occupants to block supply registers. Placement of partitions or other barriers within a space can also impair air movement. Also, locating air supply and return registers too close together can result in an uneven fresh air distribution.
• The location of all air supply vents must be carefully considered. Place supply vents as far away as possible from outdoor sources of pollution, such as loading docks, parking and heavy traffic areas, chimneys, and trash depots, provide a pathway for contaminants into the building's ventilation system.

Proportion of Outdoor Air

To dilute and eventually remove indoor contaminants, HVAC systems must bring in adequate amounts of outdoor air. However, because it is costly to heat cold winter air and to cool hot summer air, some building engineers reduce or eliminate the amount of outdoor air brought into the system during hot and cold spells; this allows contaminated air to accumulate inside, causing pollutant concentrations to increase.

Periods of Operation

An HVAC system that begins to operate after building occupants have arrived or shuts off before the end of the day can cause an increase in building-and occupant-generated pollutant levels. Also if the system is off at night and on weekends, building-generated pollutants can accumulate.

Maintenance

HVAC systems must be properly maintained to promote indoor air quality. If this is not done, ventilation systems can become a source of contamination or become clogged and reduce or eliminate air-flow. Humidification and dehumidification systems must be kept clean to prevent the growth of harmful bacteria and fungi. Failure to properly treat the water in cooling towers to prevent growth of organisms, such as Legionnella, may introduce such organisms into the HVAC supply ducts and cause serious health problems. Accumulations of water anywhere in the system may foster harmful biological growth that can be distributed throughout the building.

Economic Considerations of Air Quality

It is generally agreed that poor indoor air can adversely affect employee health and productivity. Improvements in the indoor air environment may substantially increase employee moral and productivity. Therefore, it is important to include indoor air quality controls in operation, maintenance, and energy conservation strategies.

Resolving Air Quality Problems

• Operate the ventilation system in a manner consistent with its design.
• Perform maintenance and inspections on a regular basis.
• Identify pollution sources and either remove them or use alternate venting techniques.
• Increase ventilation rates during periods of increased pollution for example: during painting, renovation, and pesticides use.
• Stay up to date on revisions to Ventilation Standards and Building Codes

Information Source: U.S. Environmental Protection Agency (EPA)

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