Ventilation Effectiveness & Indoor Air Quality Douglas Spratt February 2001

The Indoor Environment Air Indoor Environment HVAC

The Purpose of HVAC Systems

HVAC Systems: ¬ Maintain the space within the thermal comfort ­ Remove/dilute air contaminants

Ventilation- Removes Emissions SourceEmissions Reduce Remove

Ventilation Approaches n Natural n Displacement n Mechanical

Natural Ventilation n Advantages-Low 1st Cost -Low Energy -Low Maintenance -Natural -Greater occupant acceptance

Natural Ventilation n Forces-Buoyancy -Wind

Effect on Health Symptoms

Impact on Work Environment

Natural Ventilation n Limitations –Limited to Low Occupant Densities –Limited to Mild Climates –Limited Distribution

Natural Ventilation n Considerations –Security –Outdoor air quality –Wind gusts –Noise –Bugs

Displacement Ventilation

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

Air Distribution Effectiveness Source: ASHRAE 62N

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

Mechanical Ventilation n Methods –Exhaust Fan –Exhaust With Make-Up Air –Mixed Supply Air n Fixed Dampers n Modulating Dampers

The Economizer Section

20 ton Roof-top unit 9,000 cfm supply 1,000 cfm toilet exhaust 9,000 ft 2 floor space Office space with 150 ft 2 /person O/A = 20 cfm/person x 9,000 ft ft 2 /person = 1,200 cfm Example

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

Source Extraction SourceEmissions Removal Dilution Natural Mechanical Ventilation Summary