2. INTRODUCTION:
We have learned how air becomes polluted, how
vitiated air affects the occupant and the reasons for
the symptoms produced in him. It has been shown
that air movement alone cannot maintain comfortable
conditions for long without the introduction of fresh
air; no will it remove the danger of spray – borne
infections (air – bone infection).
04/21/16 2
3. In order to maintain comfortable
conditions in an occupied room it
is necessary to have adequate
ventilation. The simplest way of
doing this is to replace the warm,
humid air by cool, dry fresh air.
04/21/16 3
4. 1. Is the process of replacing foul air by that
which is pure, in any enclosed place, as a
church, a mine etc.
2. The act of supplying fresh air and get rid of
foul air.
3. Ventilation is the movement of air in and out
of an enclosed space, including a body.
04/21/16 4
5. 4.The circulation of fresh air
through open windows, doors, or
other openings, which are in
opposite sides of the room or
rooms being ventilated.
04/21/16 5
6. 5.Ventilation is the process by
which ‘clean’ air (normally outdoor
air) is intentionally provided to a
space and stale air is removed.
This may be accomplished by
either natural or mechanical
means.
04/21/16 6
7. 5.Ventilation is the intentional
movement of air from outside a
building to the inside.
04/21/16 7
9. 1.Natural ventilation
Is ventilation that occurs primarily through open
windows and doors and by infiltration through
cracks in the building envelope, such as walls,
around windows and any penetration through the
walls. Natural ventilation is driven by wind or
pressure and/or temperature differences between
inside and outside a building
04/21/16 9
10. One of the biggest advantages of
natural ventilation is that it does not
cost any money to run. Mechanical
ventilation and electronic climate
control can be quite costly, and may
contribute significantly to the overall
energy costs involved with running
a building. No use of energy also
makes natural ventilation an
environmentally friendly choice.
04/21/16 10
11. Natural ventilation systems tend
to be easier to maintain, as well,
with no parts to break or go
wrong, they can't disturb
occupants of the building with
interruptions in ventilation or add
to the operating costs for the
ventilation system
04/21/16 11
12. ◦Natural ventilation is generally
impractical for large buildings,
as they tend to be large, sealed
and climate controlled
specifically by HVAC systems.
04/21/16 12
13. Three forms of natural ventilation are:
1. Through ventilation
2. Cross ventilation
3. Back to back ventilation
04/21/16 13
14. 1. Through ventilation:
In this method the windows are
opposite to each other, so that a
current of air may pass straight
through the room.
04/21/16 14
15. 2. Cross ventilation:
In this method the windows are so placed that a
current of air may pass diagonally across the
room.
04/21/16 15
16. Cross ventilation is obtained by having windows in
both sides of the room, causing airflow across the
space. Positive pressure on the windward and/or
a vacuum on the lee side of the building causes
air movement across the room(s) from the
windward to the lee side, provided the windows on
both sides of the room are open.
04/21/16 16
17. The windows on the windward side
of the building are opened less than
the windows on the lee side, in
order to obtain an optimal airflow
with as little draught as possible.
04/21/16 17
18. 3. Back to back ventilation:
Neither through ventilation nor cross ventilation
takes place. It is considered to be unhygienic
type of ventilation, since the same air tends to be
repeatedly used without being replaced.
04/21/16 18
20. 2.Mechanical Ventilation or forced ventilation
Outside air is delivered indoors typically with a
fans, which draws air from outside and forces it
through ducts to the place where occupants are
located. Mechanical ventilation can exacerbate
infiltration and/or exfiltration
04/21/16 20
21. Three forms of artificial/mechanical ventilation
are:-
1. Exhaust (extractor/vacuum) system
2. Pressure (plenum/propulsion) system
3. Balanced system
04/21/16 21
22. 1. Exhaust (extractor/vacuum) system:
Fans draw air out of the building in openings
high up in the outside walls. The air thus drawn
out is replaced by fresh air through windows
and other inlets.
04/21/16 22
23. When it comes to air contaminants, local exhaust
ventilation is the capture of those nasties at their
source. Local exhaust ventilation is absolutely
required when the source have dust, exhaust fumes,
solvent vapors, lead fumes, and acid mist, all known
as toxic or corrosive contaminants.
04/21/16 23
24. The fans may be placed directly in windows or
outside walls or in ducts which lead the air outside.
It is a system that is useful for the removal of dust,
smoke and fumes in some factories. But the
method has the disadvantage that the flesh-air to
replace the foul (vitiated) air must find its own way
into the building.
04/21/16 24
25. 2. Pressure (plenum/propulsion) system:
Unlike the exhaust system, this forces the air into
a building and therefore control of entering air is
possible, the fresh entering air displaces the used
up air. The advantage of this method is that the
source of air-entry can be controlled and its purity
thereby ensured.
04/21/16 25
26. The air can be filtered, warmed or
cooled as required; the method
breaks down if insufficient outlets
are provided for the foul
(vitiated) air or if these are closed
or blocked up.
04/21/16 26
27. 3. Balanced system:
This is a combination of the exhaust and plenum
system.
Air is drawn in through ducts by means of a
centrifugal fan and extracted at suitable points by
exhaust fan. When this system of ventilation is
employed there should be no natural inlets or outlets.
04/21/16 27
28. A balanced ventilation system
usually has two fans and two duct
systems. It facilitates good
distribution of fresh air by placing
supply and exhaust vents in
appropriate places.
04/21/16 28
29. A typical balanced ventilation system is
designed to supply fresh air to
bedrooms and common rooms where
people spend the most time. It also
exhausts air from rooms where
moisture and pollutants are most often
generated, such as the kitchen,
bathrooms, and the laundry room.
04/21/16 29
30. Balanced ventilation systems are
appropriate for all climates;
however, because they require two
duct and fan systems, they are
usually more expensive to install
and operate than supply or exhaust
systems.
04/21/16 30
31. Air conditioning is generally employed with this
type of ventilation and the temperature and
humidity can be controlled. It is suitable for factories
where a control of humidity and temperature is
necessary to the processes being carried out; as for
example in cotton factories. It is also suitable for
cinema halls.
04/21/16 31
32. reasons for ventilation:
To keep flammable gases and vapors below the
lower flammable limit (LFL).
To keep the air movement at a certain level so that
the hear stress can be reduced.
To keep toxic contaminants at or below certain
concentrations
To reduce odors
To dilute cigarette smoke
To control microorganisms, dusts and other
particulates
To limit carbon dioxide buildup.
04/21/16 32
