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HVAC Systems and Indoor Air Quality

HVAC Systems and Indoor Air Quality

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HVAC Systems and Indoor Air Quality

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  1. HVAC Systems andIndoor Air Quality Douglas K. Spratt, M.Sc., P.Eng.

  2. The 5 Senses

  3. HVAC Systems are Dynamic

  4. Presentation Agenda • Why We Have HVAC Systems • Definitions • HVAC Control Strategies • HVAC Pollutant • HVAC Systems

  5. The Purpose of HVAC Systems HVAC = Artificial Environment

  6. The IAQ Lexicon • Acceptable IAQ: 1. No known contaminants of harmful Concentration (objective) 2. >80% people satisfied with air quality (subjective) • Sick Building Syndrome: • 1. > 20% people complaining over 2 weeks • 2. Symptoms only occur when in building •  Headaches  Eye irritation •  Fatigue  Throat irritation •  Nausea

  7. More Definitions • cfm: cubic feet per minute (flow rate) cfm/person - usually refers to outdoor air • ACH: Air Change Rate (per hour) Example: Office 10’ x 10’ x 8’ high, with one person Supply air = 120 cfm Outdoor air = 20% of S/A = 24 cfm/person Air change = (120ft3/min)(10x10x8/) x 60 min/h = 9 ACH

  8. More Definitions • Conscienceness: that annoying state in between naps. • Dopelar effect: the tendency of stupid ideas to seem smarter when you come at them rapidly.

  9. HVAC Control Strategies • Outline • Ventilation • Air Cleaning • Humidification

  10. Source Emissions Remove Reduce Ventilation- removes emissions

  11. Two ContaminantControl Strategies 1. Source Extraction 2. Dilution

  12. Source Extraction • When? • Design - Velocity (100 fpm) - Minimize Working Exposure - Make Up Air

  13. Two Dilution Methods 1. Natural l Operable Windows l Infiltration 2. Mechanical l Exhaust l HVAC relief air and outdoor air

  14. Natural Ventilation • Advantages - Low 1st Cost - Low Maintenance - Natural (“green”)

  15. Natural Ventilation • Disadvantages • Limited to Low Occupant Densities • Limited to Mild Climates • Poor Distribution • Uncontrollable factors

  16. Natural Ventilation • Design • Cross Drafts • Stack Effects • Hybird Systems

  17. Mechanical Ventilation • How much? • Depends on: • Type of Pollutants • Emission Rates • Ventilation Effectiveness

  18. How Much Ventilation? • ASHRAE Standard 62-89: • cfm O/A per person • or go “scientific” • Proposed Revision to 62-89 • cfm/person + cfm/ft2 • i.e., people + building • Other approaches: • Olf (thenose test) • exposure limits

  19. People & Pollution • Some emission rates correlate to people’s activities • People consume oxygen • People can have diseases which are air borne • Carbon dioxide (CO2) levels can be an indicator of overall indoor air quality

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

  21. The Economizer Section

  22. 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

  23. 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

  24. Mechanical Ventilation • Distribution Effectiveness • Grilles & Diffusers • Location

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

  26. HVAC Control Strategies • Ventilation • Air Cleaning

  27. 0.01 0.1 1.0 10 100 0.001 Gases Viruses Smoke Dust Pollens HEPA Filters 90 % Filters 80 % Filters 60 % Filters 30 % Filters Filters Micrometers

  28. R/A ASHRAE 52.1 Test Procedure Efficiencies O/A DOP 99.77% @ 0.3 Penetration Test HEPA Final Atmospheric 60-90% (Bag/Cartridge) Dust-Spot Pre Atmospheric 20-30% (Panel) Dust-Spot

  29. Filter Types • Standard (panel, pleated, bag, etc.) • Electrostatic • Sorption

  30. HVAC Control Strategies • Ventilation • Air Cleaning • Humidification

  31. Humidification • Desired Range 30 - 40% • Limitations (Covered Later) • Means Steam & Water

  32. Source Emissions Remove Reduce HVAC Pollutant Sources

  33. Ducts Sources: • Acoustic Lining • Ceiling Plenums • Tenant Changes • Dust and Moisture

  34. Ducts • Strategies • Inspection • Cleaning • Sealing

  35. Intakes • Proximity to Exhausts: • Kitchen • Flues • Vehicles • Smokers

  36. Intakes • Strategies • Discharge Location • Terminus • Velocity

  37. Moisture • Sources • Humidifiers • Cooling Towers • Cooling Coils • Uninsulated Ducts

  38. Moisture • Strategies • Eliminate • Treat

  39. Combustion • Sources • Faulty Heat Exchangers • Faulty Flues • Back Drafting

  40. Combustion • Strategies • Inspection • Testing • O/A Control