Indoor air quality
Good IAQ: a clean, healthy, and odor-free indoor environment.
“Sick Building Syndrome” (SBS) is discomfort/illness caused by indoor air. SBS is often comparable to a cold or influenza
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Health problems: 30 — 70 million people (U. S. EPA)
Health complaints: 30% new and remodeled buildings (U. S. EPA) Occupational illness: 439,000 cases in 1996 (NIOSH)
Economic loss: $40 — 120 billion/year ($200-600/person. year)
• COx, NOx and other common gases (human, combustion)
• Environmental tobacco smoke ETS (smoking)
• Volatile organic compounds VOC
(building materials: construction materials, furnishings, finishes)
• Particulate matters (outdoor air, activities, ETS)
• Biohazards (molds, bacteria, etc.)
• Radon (soil)
|
Contaminants |
Sources |
Permitted level |
Health effects |
|
Co2 |
Human, combustion |
1000 ppm |
Stuffing |
|
CO |
Combustion, ETS |
15 ppm |
Body chemistry |
|
Sox |
Combustion |
Irritation, asthma |
|
|
NOx |
Combustion |
100 |ig/m3 |
Not very clear |
|
Ra |
Soil |
4 picocuries/1 |
Lung cancer |
|
VOCs |
Combustion, |
0.1 ppm |
Eyes and mucous |
|
(Formaldehyde) |
Pesticides, building materials, etc. |
Membrane irritation |
|
|
Particulate |
Outdoor air, |
Lung diseases |
|
|
(0.01 micro-insects) |
Activities, ETS, furnishings, pets, etc |
Cancer (ETS) |
The following diagram illustrates the buildup of indoor carbon dioxide (due to occupant exhalation) throughout a normal day:
|
|
|
Carbon Dioxide Concentration (ppm) |
Results |
|
250-350 |
Normal outdoor ambient air |
|
600 |
Minimal air quality complaints |
|
600-1000 |
Effect on indoor air quality is less clearly interpreted |
|
1000 |
Indicates inadequate ventilation; indoor air quality complaints are more widespread |
Common Causes of Poor Indoor Air Quality (IAQ)
Tight buildings (Energy conservation)=>
=>Less outdoor air (Infiltration) =>
=>High contaminant concentrations (New building materials release VOCs)
Numerous indoor air quality investigations over the last decade by the National Institute for Occupational Safety & Health (NIOSH) have found the primary source of indoor air quality problems are:
Inadequate ventilation 52%
Contaminant from inside the building 16%
Contaminant from outside the building 10%
Microbial contamination 5%
Contamination from building fabric 4%
Unknown Sources 13%
Control of contaminants
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New parameters
Supply air — Total air supplied to a space
Fresh air — Outdoor air
Infiltration — Uncontrolled air entered to a space
Exfiltration — Uncontrolled air left a space
For mechanical ventilated space, infiltration should be zero because of positive pressure in the conditioned space.
Most common method for contaminant control is ventilation. Ventilation can be either natural or forced. Ventilation dilutes contaminants with outdoor air, and requirements are defined by state/local codes and referenced standards.
ANSI/ASHRAE Standard 62-1999:
Ventilation for Acceptable Indoor Air Quality
Defines:
• Acceptable outdoor air quality
• Procedure for acceptable ventilation
Posted in Fundamentals of Heating. Ventilating, and Air-Conditioning