Types of ventilation

1. Ventilation
By : Jagdish Palariya
Roll No. - 14

2. Contents
1. Definition
2. Fundamentals of
Ventilation
3. Purposes of
Ventilation
4. Classification &
Types of Ventilation
5. Natural
Ventilation & Its
Types
6. Mechanical
Ventilation & Its
Types
7. Local Exhaust
Ventilation
8. LEV Components
9. Advatages &
disadavtages of
Dilution & Local
Exhaust Ventilation

3. Ventilation Definition
• Ventilation is the mechanical system in a building that brings in "fresh"
outdoor air and removes the "contaminated" indoor air.
• Ventilation is considered an "engineering control" to remove or control
contaminants released in indoor work environments. It is one of the preferred
ways to control employee exposure to air contaminants.
• In a workplace, ventilation is used to control exposure to airborne
contaminants. It is commonly used to remove contaminants such as fumes,
dusts, and vapours, in order to provide a healthy and safe working
environment.

4. Fundamentals
of ventilation
• Why is it necessary to ventilate?
• Air for breathing
• Adult man has frequency of
breathing typically 16 times per
minute – 8 l/min.Oxygen
consumption varies between 250 –
350 ml/min.
• Respiration Into lungs(atmospheric
air) - 21 % O2, 78 % N2, 0.03 % CO2
• Out from lungs - 16 % O2, 79 % N2, 4
% CO2(plus water vapor).

5. Purposes
of
ventilation
• There are four purposes of
ventilation:
• 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.

6. Classification
of
Ventilation
Systems Major ventilation systems
are classified as:

7. Types of
Ventilation
systems
• Ventilation systems are of two types
1. Supply air system :- Supply air system has two
purposes
• heating, ventilating and air conditioning
(HVAC) for comfortable environment
• to replace exhausted air from the plant.
2. Exhaust system:-Exhaust system is of two
types:
1.General exhaust Type
• General exhaust system is for heat
control and/or removal of contaminant
by dilution ventilation
2.Local exhaust type.
• Local exhaust system is for capturing
contaminant at source.

8. Natural
Ventilation
• The process of pulling fresh air
into a building from the outside.
In turn, this fresh air helps force
the warm, dirty air inside of the
building out through the opening
in the roof. This is done, without
any mechanical assistance.
• Natural Ventilation are of two
types:
• Dilution or crossed ventilation
• Roofed Ventilation or stack effect

9. Dilution Ventilation or Cross ventilation
• Inlet openings should be located on the windward
side at a low level and outlet openings should be
located on the leeward side near to the top so that
incoming air stream is passed over the occupants.
• Greatest flow per unit area opening is obtained by
using inlet and outlet openings of nearly equal
areas.
• Inlet openings should not be obstructed by
surrounding buildings, walls, partitions, trees and
other obstructions in air path.

10. Roofed Ventilation or
Stacked effect
• It seems complicated, but it works
basically like a fireplace. Because warm
air rises and cool air stays low, this
process forces warm air up.
• Cross ventilation suitable for narrow
building is not much suitable for large
buildings and where roofed ventilation is
suitable.
• Here ventilators are provided in roofs viz.
cowl, vent pipe, covered roof and ridge
vent to give stack effect.

12. Mechanical Ventilation-
• Forced ventilation works on the principle
that fresh air flow is provided by
mechanical ventilators. Most common
solutions are either mechanically forced
exhaust or mechanically forced supply
and exhaust.
• The advantage of mechanical ventilation
is that the required interior climate can
be achieved with changing the settings of
the system no matter what the outdoor
weather conditions might be.

13. Types of Mechanical Ventilation System:
Exhaust or Negative Ventilation
• Exhauster induced draft fans are
provided in walls on one side of the
building or in the attic and roofs to
draw large volumes of air through
building. These fans are generally
propeller type.
• The windows and other openings near
the fans should be kept closed to avoid
'short circulating of air'. Adequate inlet
openings shall be provided on opposite
side of the building to limit inlet
velocities.

14. Types of Mechanical Ventilation System:
Plenum or Positive Ventilation
(Forced Draft)
• It is provided by centrally located supply fans
(generally centrifugal type) having a wide range
of capacity and quiet operation. Air-tight ducts
increase the advantage.
• Plenum ventilation is useful for large
workrooms where exhaust ventilation is
normally not effective.
• The positive air pressure inside the room
disallows outside hot or cold air leakage inside.'
Better dilution is achieved.
• Discharge nozzles should discharge air
horizontally at a height little above the heads of
the workers

15. Types of
Mechanical
Ventilation
System:
Combined
(Compound)
Ventilation
• It is the combination of positive and negative
(exhaust) ventilation with the advantage of
better air distribution over the entire area of
a large building.
• By supplying proper volumes of air at
suitable velocities at the required areas
through duct and by extracting the air in the
return duct and re-circulating this air after
proper cleaning and mixing it with cool fresh
air, good results can be obtained.

16. Types
of Mechanical Ventilation System:
Mechanical Roof Ventilation

17. Types of Mechanical Ventilation System:
Dilution or Forced Ventilation
• Dilution ventilation uses clean air
(forced air) to dilute the contaminated
air and then exhausts the diluted air to
the outside via exhaust fans
• It is helpful in reducing contaminant
concentration in work area to control
health and fire hazards.
• Dilution ventilation controls pollutants
generated at a worksite by ventilating
the entire workplace.

18. Types of Mechanical Ventilation System:
Local Exhaust Ventilation
• In specially hazardous operations, a local
exhaust system may be required to effectively
control atmospheric contamination at its
source.
• Local exhaust ventilation involves trapping
airborne contaminants at their source before
they contaminate the air that is breathed by
workers.
• For welding, cutting and heating processes,
this type of ventilation must consist of freely
movable hoods placed by the welder or burner
as close as possible to where the work is being
performed.
• A local exhaust system should normally contain
an enclosing hood, ducting, an air cleaner and
an exhaust fan.

19. Local
Exhaust
Ventilation:
LEV
components
HOOD
DUCTING
AIR CLEANER
FAN
EXHAUST STACK

20. LEV components:
1. Hood
The hood captures contaminated
air. To be effective, the hood:
• should be as close as possible to
the source of the contaminated
air
• should enclose the work area as
much as possible. This helps
avoid draughts that can blow
contaminated air into the
workplace
• must be suitable for the work
being done and the type of
substance produced (for
example, dust or fumes).
• Types Of LEV Hood
• Enclosing hoods
• Capturing hoods

21. LEV components:
Types of Hoods
• Enclosing hoods(Fig 1)
• enable contaminated air to be contained.
• protects the operator and prevents contaminated
air from entering the work area.
• Capturing hoods(Fig 2)
• Capturing hoods are the most common type of LEV
hood. The work occurs outside the hood.
• This type of hood requires the LEV system to
generate enough airflow to draw in the
contaminated air.
• There are several types of capturing hoods: on-
tool, moveable capturing hoods, fixed, portable or
flexible capturing hoods and extracted
workbenches.
Fig. 2
Fig. 1

22. LEV components:
Ducting & Air Cleaner
DUCTING
• Contaminated air travels through the ducting system to the air cleaner.
• Choose a ducting system that has no sharp corners and which is easy to access for
assessment, maintenance and cleaning.
• Ducting systems have been known to collapse under the weight of dust deposits,
or to catch fire due to dust buildup.
AIR CLEANER
• The air cleaner filters the contaminated air.
• Choose air cleaners with filters that are suitable for the contaminant and that can
be easily cleaned or replaced without creating further exposure.

23. LEV
components:
Fan
& Exhaust
Stack
FAN
• Fans that move the air through the system and
discharges the exhaust air outdoors.
• The fan should be positioned so that it can be
easily maintained but does not create a noise
hazard for nearby workers.
EXHAUST FAN
• An exhaust stack through which the
contaminated air is discharged.
• It should be positioned on the outside wall of
the building, or through the roof,