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GENERAL VENTILATION

GENERAL VENTILATION. …examination of the use of “fresh air” to dilute contaminants to acceptable levels. Applications of General Ventilation. dilution of airborne contaminants to acceptable levels control fire/explosion risks minimize odors or other nuisances maintain “comfort”.

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GENERAL VENTILATION

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  1. GENERAL VENTILATION …examination of the use of “fresh air” to dilute contaminants to acceptable levels

  2. Applications of General Ventilation • dilution of airborne contaminants to acceptable levels • control fire/explosion risks • minimize odors or other nuisances • maintain “comfort”

  3. Natural Ventilation • always a factor via infiltration, etc. • design of natural ventilation via • pressure gradient • air density difference • equations/examples

  4. Mechanical Ventilation • creation of air flow by “artificial” means • usually required because infiltration is low volume & not controllable • general ventilation vs local exhaust

  5. General Ventilation May be OK • IF... • air contaminants are of low toxicity • concentrations are not high/hazardous • emission rate is fairly low & constant • contaminant sources are dispersed • other solutions are less practical • uncontaminated “fresh air” is available

  6. …and usually is NOT Ok if... • contaminants are moderately toxic • concentrations are high/hazardous • emissions vary with time, e.g. batch operation. • air must pass through breathing zone • re-entrainment of contaminant is likely • control at source is more appropriate

  7. DESIGNPRINCIPLES • determine amount of air required • locate exhaust near source • establish appropriate air flow pattern • replace exhausted air • avoid re-entry of exhausted air

  8. HVAC Standards Affecting IAQ • ASHRAE 62-1999: Ventilation for Acceptable Air Quality • ASHRAE 55-1992: Thermal Environmental Conditions for Human Occupancy • ASHRAE 52-1992: Methods of Testing Air Cleaning Devices Used in General Ventilation for Removing Particulate Matter • Proposed OSHA IAQ Standard

  9. OA Required for Specific Occupancies (ASHRAE 62-1999)

  10. Causes of IAQ Problems • Deficiencies in ventilation of the building • Indoor air contaminants • Outdoor sources • No identified cause

  11. Equations • Calculating Dilution Air Volumes • For health protection (where target concentration is PEL/TLV) • Pure • Mixtures • If solvent produce similar (additive) effects, the total dilution air required must be determined by calculating volume for each solvent and summing • If solvents do not produce similar effects, the largest volume calculated for individual components should be used • If any doubt about additive effects, assume they are additive • For fire and explosion protection (where target concentration is LEL) • Does not apply where workers are exposed to vapors. In these cases, the dilution rates above for health protection should always be used • Air density adjustment

  12. K Factor Some considerations that may be looked at in determining the K Factor: • The mixing and distribution of replacement air • The toxicity of the solvent • Duration of process • Location of workers to sources • Location and number of points of generation • Changes in ventilation systems K

  13. Role of IH? • Understand HVAC system components • Determine operating parameters • Perform ventilation checks

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