Lecture 16 (Ventilation) Flashcards
IAQ
Remove or control: Hazardous/ obnoxious odors Asbestos Chemicals Gases etc.
IAQ Related illnesses
Pontiac fever
Sinusitis
Legionnaires disease (10-20% mortality)
Ventilation Purposes
Provide a continuous supply of fresh outside air
Maintain temperature and humidity at comfortable levels
Reduce potential fire or explosion hazards
Remove or dilute airborne contaminants
Ventilation Steps
What the problem is Location of problem Type of structure/building layout Identify source Locate the source Is it safe for me and others? If unknown or dangerous; follow operation policy
Ventilation Types
Vertical: Moving air up and out
Horizontal: Moving air out through windows and doors
Ventilation System Types
Local Exhaust Ventilation:
Captures/Removes the contaminant at or near its source
General Dilution Ventilation:
Diluting the concentration of the contaminant(s)
Local Exhaust System
There are four elements that make up a local exhaust: The hood The ductwork The air cleaning device The fan
Hood
Captures the contaminant by overcoming its momentum and then drawing it into the system
Velocities Required are:
100 fpm for vapours and gases
200 fpm or more for dusts
Duct
Provides a pathway to carry the contaminant to the air cleaning device.
Velocities required are:
1000 fpm for vapours and gases
4000 fpm for heavy dusts
Air Flow
Air moves when there is a pressure difference between two locations
Q = VA
Natural Air Flow
No cost
Difficult to control
Increased time to utilize
Forced Air Flow
Easy to control direction
Need power source
Fumes
Cost
Air Cleaning Devices
Mechanical Separators Filtration Devices Wet Collectors Electrostatic Precipitators Gas Collection Combustion Incinerators
Ventilation Measurements
Smoke Tubes
Anemometers
Mechanical Seperators
Gravity chambers
Impingement separators
Cyclone collectors or separators
Cyclone collectors or separators
contaminated rotating gas causes particulates to move to the outside of the rotating column
The particulates fall to the bottom and exit through a port
Particles smaller than 5 μm are not collected
Relatively low cost
Impingement Separators
Dust-laden air passes through a network of baffles
Particulates have more momentum and cannot make the quick turns
Not used for particles smaller than 20 μm
Gravity chambers
low-cost collection devices
works when the air velocity is very slow for large particles
Filtration Devices
Mat filters
Ultrafiltration filters
Fabric filters
Fabric filters
Air moves through the fabric bags and dust collects inside them
Choose filter based on type of containment and air temperature
Ultrafiltration Filters
HEPA remove a wide range of particles
Require considerable maintenance
Have high- pressure drops across them
Mat Filters
Made of glass fibers. some are disposable, others are washable
