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Ventilation Rates and Technologies
What is The Effect of Ventilation System Type on Occupants?
Several studies have found that the type of ventilation system is linked to the prevalences of sick building syndrome (SBS) experienced by building occupants.
- Air conditioning is consistently associated with symptoms relative to natural ventilation.
- There is some evidence that mechanical ventilation without air conditioning is associated with symptoms.
- The causes of the association are unclear, but there is evidence that moisture and contamination of HVAC plays a role.
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| HVAC System Type | Risks | ||
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| Natural ventilation with operable windows |
No particle removal via filtration; poor indoor temperature and control; noise from outdoors; inability to control the
pressure difference across the building envelope and exclude pollutant infiltration or penetration of moisture into structure; low
ventilation rates during some weather conditions; possible low ventilation rates in some portions of the occupied space. |
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Systems with ducts and fans but no cooling or humidification (simple mechanical ventilation) |
HVAC components may be dirty when installed or become dirty and release pollutants and odors; poor control of indoor temperature
due to absence of cooling; low humidity in winter in cold climates; high humidity during periods of humid weather; noise
generated by forced air flow and fans; draft caused by forced air flows. |
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Systems with ducts, fans and cooling coils (air conditioning systems) |
Additional risk factors from cooling coils: very high relative humidity or condensed moisture (e.g. in cooling coils and drain pans)
and potential microbial growth; biocides used to treat wet surfaces such as drain pans and sometimes applied to nearby insulation. |
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| Systems with ducts fans, cooling coils and humidifiers of various types |
Additional risk from humidifiers: microbial growth in humidifiers; transport of water droplets downstream of humidifiers causing
wetting of surfaces; leakage and overflow of humidifier water; condensation from high-humidity air; biocides in humidifiers;
chemical water treatments in steam generators. |
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Systems with recirculation of return air (recirculation may occur in all mechanical HVAC systems) |
Additional risks* from recirculation: indoor-generated pollutants are spread throughout the section of building served by the
air handling system; typically higher indoor air velocities increase risk of draft and HVAC noise; supply ducts and filters of
HVAC system may become contaminated by recirculated indoor-generated pollutants. |
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Sealed or openable windows (windows may be sealed or openable with all types of mechanical HVAC systems) |
Additional risk with sealed windows: no control of the environment if HVAC systems fails; psychological effect of isolation from outdoors. Additional risk with openable windows: more exposure to outdoor noise and pollutants. | ||
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Decentralized systems (cooling and heating coils located throughout building, rather than just in mechanical rooms) |
Additional risk of decentralization: potentially poorer maintenance because components are more numerous or less accessible. Potentially more equipment failures due to larger number of components. | ||
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* However, recirculation facilitates removal of indoor-generated pollutants using air cleaners, e.g. particle filters, and may also decrease concentrations of pollutants near pollutant sources.
Table 4. Comparison of SBS symptom prevalences with and without air conditioning.
Table 5. Comparisons of symptom prevalences among buildings without air conditioning.
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