1. Industrial Ventilation
General Principles of Industrial Ventilation

2. What Is Industrial Ventilation?
Environmental engineer’s view:
The design and application of equipment for providing the necessary conditions for maintaining the efficiency, health and safety of the workers
Industrial hygienist’s view:
The control of emissions and the control of exposures
Mechanical engineer’s view:
The control of the environment with air flow. This can be achieved by replacement of contaminated air with clean air
General Principles

3. Industrial Ventilation
Objectives
To introduce the basic terms
To discuss heat control
To design ventilation systems
General Principles

4. Why Industrial Ventilation?
To maintain an adequate oxygen supply in the work area.
To control hazardous concentrations of toxic materials in the air.
To remove any undesirable odors from a given area.
To control temperature and humidity.
To remove undesirable contaminants at their source before they enter the work place air.
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5. Application Of Industrial Ventilation Systems
Optimization of energy costs.
Reduction of occupational health disease claims.
Control of contaminants to acceptable levels.
Control of heat and humidity for comfort.
Prevention of fires and explosions.
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6. Solutions To Industrial Ventilation Problems
Process modifications
Local exhaust ventilation
Substitution
Isolation
Administrative control
Personal protection devices
Natural ventilation
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7. Ventilation Design Parameters
Manufacturing process
Exhaust air system & local extraction
Climatic requirements in building design (tightness, plant aerodynamics, etc)
Cleanliness requirements
Ambient air conditions
Heat emissions
Terrain around the plant
Contaminant emissions
Regulations
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8. Source Characterization
Location
Relative contribution of each source to the exposure
Characterization of each contributor
Characterization of ambient air
Worker interaction with emission source
Work practices
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9. Types Of Industrial Ventilation Systems
Supply systems
Purpose:
To create a comfortable environment in the plant i.E. The HVAC system
To replace air exhausted from the plant i.E. The replacement system
General Principles

10. Supply Systems Components Air inlet section Filters
Heating and/or cooling equipment
Fan
Ducts
Register/grills for distributing the air within the work space
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11. Exhaust Systems Purpose
An exhaust ventilation system removes the air and airborne contaminants from the work place air
The exhaust system may exhaust the entire work area, or it may be placed at the source to remove the contaminant at its source itself
General Principles

12. Exhaust Systems Types of exhaust systems: General exhaust system
Local exhaust system
General Principles

13. General Exhaust Systems
Used for heat control in an area by introducing large quantities of air in the area. The air may be tempered and recycled.
Used for removal of contaminants generated in an area by mixing enough outdoor air with the contaminant so that the average concentration is reduced to a safe level.
General Principles

14. Local Exhaust Systems(LES)
The objective of a local exhaust system is to remove the contaminant as it is generated at the source itself.
Advantages:
More effective as compared to a general exhaust system.
The smaller exhaust flow rate results in low heating costs compared to the high flow rate required for a general exhaust system.
The smaller flow rates lead to lower costs for air cleaning equipment.
General Principles

15. Local Exhaust Systems(LES)
Components:
Hood
The duct system including the exhaust stack and/or re-circulation duct
Air cleaning device
Fan, which serves as an air moving device
General Principles

16. What is the difference between Exhaust and Supply systems?
An Exhaust ventilation system removes the air and air borne contaminants from the work place, whereas, the Supply system adds air to work room to dilute contaminants in the work place so as to lower the contaminant concentrations.
General Principles

17. Pressure In A Ventilation System
Air movement in the ventilation system is a result of differences in pressure.
In a supply system, the pressure created by the system is in addition to the atmospheric pressure in the work place.
In an exhaust system, the objective is to lower the pressure in the system below the atmospheric pressure.
General Principles

18. Types Of Pressures In A Ventilation Systems
Three types of pressures are of importance in ventilation work. They are:
Static pressure
Velocity pressure
Total pressure
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19. Why is air considered incompressible in Industrial Ventilation design problems?
The differences in pressure that exist within the ventilation system itself are small when compared to the atmospheric pressure in the room. Because of the small differences in pressure, air can be assumed to be incompressible.
Since 1 lb/in2 = 27 inches of water, 1 inch = lbs pressure or 0.24% of standard atmospheric pressure. Thus the potential error introduced due to this assumption is also negligible.
General Principles

20. Velocity Pressure
It is defined as that pressure required to accelerate air from rest to some velocity (V) and is proportional to the kinetic energy of the air stream.
VP acts in the direction of flow and is measured in the direction of flow.
VP represents kinetic energy within a system.
VP is always positive.
General Principles

21. Static Pressure
It is defined as the pressure in the duct that tends to burst or collapse the duct and is expressed in inches of water gauge (“wg).
SP acts equally in all directions
SP can be negative or positive
General Principles

22. Static pressure can be positive or negative.Explain.
Positive static pressure results in the tendency of the air to expand. Negative static pressure results in the tendency of the air to contract.
For example, take a common soda straw, and put it in your mouth. Close one end with your finger and blow very hard. You have created a positive static pressure. However, as soon as you remove your finger from the end of the straw, the air begins to move outward away from the straw. The static pressure has been transformed into velocity pressure, which is positive.
General Principles

23. Velocity Pressure VELOCITY PRESSURE (VP) VP = (V/4005)2 or V = 4005√VP
Where
VP = velocity pressure, inches of water gauge (“wg)
V = flow velocity, fpm
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24. Total Pressure TP = SP + VP
It can be defined as the algebraic sum of the static as well as the velocity pressures
SP represents the potential energy of a system and VP the kinetic energy of the system, the sum of which gives the total energy of the system
TP is measured in the direction of flow and can be positive or negative
General Principles

25. How do you measure the Pressures in a ventilation system?
The manometer, which is a simple graduated U-shaped tube open, at both ends, an inclined manometer or a Pitot tube can be used to measure Static pressure.
The impact tube can be used to measure Total pressure.
The measurement of Static and Total pressures using manometer and impact tube, will also indirectly result in measurement of the Velocity pressure of the system.
General Principles

26. Basic Definitions Pressure It is defined as the force per unit area.
Standard atmospheric pressure at sea level is inches of mercury or 760 mm of mercury or 14.7 lb/sq.inch.
General Principles

27. Basic Definitions Air density
It can be defined as the mass per unit volume of air, (lbm/ft3 ). at standard atmosphere (p=14.7 psfa), room temperature (70 F) and zero water content. The value of ρ=0.075 lbm/ft3
General Principles

28. Basic Definitions Perfect Gas Equation: P = ρRT Where
P = absolute pressure in pounds per square foot absolute (psfa).
ρ = gas density in lbm/ft3.
R = gas constant for air.
T = absolute temperature in degree Rankin.
For any dry air situation
ρT = (ρT)std
ρ = ρstd(Tstd/T) = (460+70)/T = (530/T)
General Principles

29. Basic Definitions Volumetric Flow Rate
The volume or quantity of air that flows through a given location per unit time
Q = V * A or
V = Q /A
A = Q/V
Where
Q = volume of flow rate in cfm
V = average velocity in fpm
A = cross-sectional area in sq.ft
General Principles

30. Example
The cross-sectional area of a duct is 2.75 sq.ft.The velocity of air flowing in the duct is fpm. What is the volume?
From the given problem
A = 2.75 sq. ft.
V = 3600 fpm
We know that
Q = V * A
Hence,
Q = 3600 * 2.75 = 9900 cfm
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31. Basic Definitions Reynolds number R = ρDV/μ Where
ρ = density in lbm/ft3
D = diameter in ft
V = velocity in fpm
μ = air viscosity, lbm/s-ft
General Principles

32. Darcy Weisbach Friction Coefficient Equation
hf = f (L/d)VP
Where
hf = friction losses in a duct, “wg
f = friction coefficient (dimensionless)
L = duct length, ft
d = duct diameter, ft
VP = velocity pressure,”wg
General Principles

33. Duct Losses Types of losses in ducts Friction losses
Dynamic or turbulence losses
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34. Duct Losses Friction losses Factors effecting friction losses:
Duct velocity
Duct diameter
Air density
Air viscosity
Duct surface roughness
General Principles

35. Duct Losses Dynamic losses or turbulent losses
Caused by elbows, openings, bends etc. In the flow way. The turbulence losses at the entry depends on the shape of the openings
Coefficient of entry (Ce)
For a perfect hood with no turbulence losses Ce = 1.0
I.E
V = 4005ce√VP = 4005 √VP
General Principles

36. Duct Losses Turbulence losses are given by the following expression
Hl= FN*VP
Where
FN = decimal fraction
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37. Terminal Or Settling Velocity
V = (S.G)D2
Where
D = particle diameter in microns
S.G = specific gravity
V = settling velocity in fpm
General Principles