HVAC Systems and
Indoor Air Quality
Douglas K. Spratt, M.Sc., P.Eng.
The 5 Senses
Hearing
Architecture Electrical Structural Mechanical
Smelling
Seeing
Feeling
Tasting
HVAC Systems are Dynamic
Heat Gains
Response
Loads
Solar
Required Air
Conditioning
Lights
People
Equipment
Outdoor
temperature
Presentation Agenda
= Why We Have HVAC Systems
= Definitions
= HVAC Control Strategies
= HVAC Pollutant
= HVAC Systems
The Purpose of HVAC
Systems
H
V
Thermal Control (ASHRAE - 55)
Air Quality (ASHRAE - 62)
(Contaminant Control)
A
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 Eye irritation
Fatigue Throat irritation
Nausea
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
G cfm/ person + cfm/ ft
2
G i.e., people + building
= Other approaches:
G Olf (the nose test)
G exposure limits
People & Pollution
= Some emission rates correlate to
peoples 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
OUTDOOR
SUPPLY
MIXED
RECIRCULATED
M-2
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
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
Mechanical Ventilation
= Distribution Effectiveness
Grilles & Diffusers
Location
Ventilation Summary
Source
Extraction
Source Emissions
Removal
Dilution
Natural
Mechanical
HVAC Control Strategies
= Ventilation
= Air Cleaning
Filters
Gases
HEPA Filters
90 % Filters
80 % Filters
60 % Filters
30 % Filters
0.001 0.01 0.1 1.0 10 100
Viruses
Smoke
Dust
Pollens
Micrometers
ASHRAE 52.1
Test Procedure Efficiencies
O/A
R/A
HEPA
DOP
Penetration Test
99.77% @ 0.3
60-90%
20-30%
Final
(Bag/Cartridge)
Atmospheric
Dust-Spot
Atmospheric
Dust-Spot
Pre
(Panel)
Filter Types
= Standard (panel, pleated, bag, etc.)
= Electrostatic
= Sorption
HVAC Control Strategies
= Ventilation
= Air Cleaning
= Humidification
Humidification
= Desired Range 30 - 40%
= Limitations (Covered Later)
= Means Steam & Water
HVAC Pollutant Sources
Emissions
Reduce Remove
Source
Ducts
Sources:
G Acoustic Lining
G Ceiling Plenums
G Tenant Changes
G 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
