HVAC Systems and Indoor Air Quality Douglas K. Spratt, M.Sc., P.Eng.
The 5 Senses Architecture Electrical Structural Mechanical Hearing Seeing Smelling Feeling Tasting
HVAC Systems are Dynamic Heat Gains Solar Response Loads Outdoor temperature Lights Required Air Conditioning People Equipment
Presentation Agenda Why We Have HVAC Systems Definitions HVAC Control Strategies HVAC Pollutant HVAC Systems
The Purpose of HVAC Systems H V A Thermal Control (ASHRAE - 55) Air Quality (ASHRAE - 62) (Contaminant Control) C HVAC = Artificial Environment
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 Fatigue Nausea Eye irritation Throat irritation
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 = (120ft 3 /min) (10x10x8/) x 60 min/h = 9 ACH
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.
HVAC Control Strategies Outline Ventilation Air Cleaning Humidification
Ventilation - removes emissions Source Emissions Reduce Remove
Two Contaminant Control Strategies 1. Source Extraction 2. Dilution
Source Extraction When? Design - Velocity (100 fpm) - Minimize Working Exposure - Make Up Air
Two Dilution Methods 1. Natural Operable Windows Infiltration 2. Mechanical Exhaust HVAC relief air and outdoor air
Natural Ventilation Advantages - Low 1st Cost - Low Maintenance - Natural ( green )
Natural Ventilation Disadvantages Limited to Low Occupant Densities Limited to Mild Climates Poor Distribution Uncontrollable factors
Natural Ventilation Design Cross Drafts Stack Effects Hybird Systems
Mechanical Ventilation How much? Depends on: Type of Pollutants Emission Rates Ventilation Effectiveness
How Much Ventilation? ASHRAE Standard 62-89: cfm O/A per person or go scientific Proposed Revision to 62-89 cfm/person + cfm/ft 2 i.e., people + building Other approaches: Olf (the nose test) exposure limits
People & Pollution Some emission rates correlate to people s activities People consume oxygen People can have diseases which are air borne Carbon dioxide (CO 2 ) levels can be an indicator of overall indoor air quality
Mechanical Ventilation Methods Exhaust Fan Exhaust With Make-Up Air Mixed Supply Air Fixed Dampers Modulating Dampers
The Economizer Section EXHAUST RETURN RECIRCULATED OUTDOOR M-2 MIXED SUPPLY M-1
Example 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 62-89 O/A = 20 cfm/person x 9,000 ft 2 150 ft 2 /person = 1,200 cfm
Ignoring Infiltration 200 cfm 1,000 cfm R/A 8,000 cfm 7,800 cfm 1,200 cfm S/A 9,000 cfm T/E % O/A = 1,200 cfm = 13% 9,000 cfm
Mechanical Ventilation Distribution Effectiveness Grilles & Diffusers Location
Ventilation Summary Source Emissions Removal Source Extraction Natural Dilution Mechanical
HVAC Control Strategies Ventilation Air Cleaning
Filters Gases Viruses Smoke Dust Pollens Micrometers 0.001 0.01 0.1 1.0 10 100 HEPA Filters 90 % Filters 80 % Filters 60 % Filters 30 % Filters
O/A R/A ASHRAE 52.1 Test Procedure Efficiencies HEPA DOP Penetration Test Final (Bag/Cartridge) Atmospheric Dust-Spot Pre (Panel) Atmospheric Dust-Spot 99.77% @ 0.3 60-90% 20-30%
Filter Types Standard (panel, pleated, bag, etc.) Electrostatic Sorption
HVAC Control Strategies Ventilation Air Cleaning Humidification
Humidification Desired Range 30-40% Limitations Means (Covered Later) Steam & Water
HVAC Pollutant Sources Source Emissions Reduce Remove
Ducts Sources: Acoustic Lining Ceiling Plenums Tenant Changes Dust and Moisture
Ducts Strategies Inspection Cleaning Sealing
Intakes Proximity to Exhausts: Kitchen Flues Vehicles Smokers
Intakes Strategies Discharge Location Terminus Velocity
Moisture Sources Humidifiers Cooling Towers Cooling Coils Uninsulated Ducts
Moisture Strategies Eliminate Treat
Combustion Sources Faulty Heat Exchangers Faulty Flues Back Drafting
Combustion Strategies Inspection Testing O/A Control