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Ventilation Effectiveness & Indoor Air Quality

Ventilation Effectiveness & Indoor Air Quality. Douglas Spratt February 2001. Indoor Environment. Air. HVAC. The Indoor Environment. The Purpose of HVAC Systems. HVAC Systems:. Maintain the space within the thermal comfort Remove/dilute air contaminants. Source. Emissions. Remove.

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Ventilation Effectiveness & Indoor Air Quality

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  1. Ventilation Effectiveness & Indoor Air Quality Douglas Spratt February 2001

  2. Indoor Environment Air HVAC The Indoor Environment

  3. The Purpose of HVAC Systems

  4. HVAC Systems: • Maintain the space within the thermal comfort • Remove/dilute air contaminants

  5. Source Emissions Remove Reduce Ventilation- Removes Emissions

  6. Ventilation Approaches • Natural • Displacement • Mechanical

  7. Natural Ventilation • Advantages - Low 1st Cost - Low Energy - Low Maintenance - Natural - Greater occupant acceptance

  8. Natural Ventilation • Forces - Buoyancy - Wind

  9. Effect on Health Symptoms

  10. Impact on Work Environment

  11. Natural Ventilation • Limitations • Limited to Low Occupant Densities • Limited to Mild Climates • Limited Distribution

  12. Natural Ventilation • Considerations • Security • Outdoor air quality • Wind gusts • Noise • Bugs

  13. Displacement Ventilation

  14. Continuously purges air pollutants Typical features: - De-couples ventilation - Uses natural buoyancy forces - Low noise - No drafts - Fresh air breathing zone Displacement Ventilation

  15. Air Distribution Effectiveness Source: ASHRAE 62N

  16. Mechanical Ventilation Practical Help • Watch for short circuiting • Min. O/A settings for VAV Systems • Ensure continuous fan operation

  17. Mechanical Ventilation • Methods • Exhaust Fan • Exhaust With Make-Up Air • Mixed Supply Air • Fixed Dampers • Modulating Dampers

  18. The Economizer Section

  19. 62-89 O/A = 20 cfm/person x 9,000 ft2 150 ft2/person = 1,200 cfm Example 20 ton Roof-top unit 9,000 cfm supply 1,000 cfm toilet exhaust 9,000 ft2 floor space Office space with 150 ft2/person

  20. 200 cfm 1,000 cfm R/A 8,000 cfm 7,800 cfm S/A 9,000 cfm 1,200 cfm T/E % O/A = = 13% 9,000 cfm Ignoring Infiltration 1,200 cfm

  21. Source Emissions Removal Source Extraction Dilution Natural Mechanical Ventilation Summary

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