Ventilation is the process of changing or replacing air in an enclosed space to control air quality by removing contaminants and introducing outside fresh air. It is needed to maintain oxygen levels, remove carbon dioxide, control humidity, prevent heat buildup, and dilute odors and other contaminants. Ventilation can be natural through wind and stack effects, or mechanical using fans. Standards recommend minimum air change rates to ensure adequate indoor air quality and occupant comfort. Factors like air temperature, humidity, airflow patterns, and rates must be properly controlled.

1. VENTILATION
QSB 1714
Prepared by: Zhermeica Lim

2. INTRODUCTION
Definition:
 The process of changing air in an enclosed
space.
 A proportion of air within the enclosed space
should be continuously withdrawn and
replaced by fresh air.
 Drawn in from a clean external source:
 At as high an elevation as practical…where
more polluted air occurs at the relatively low
levels found in congested towns and cities.

3. Why do we need ventilation?

4. Ventilation is needed to maintain air purity…

5. which is......

6. 1. Preservation of oxygen content.
 This should be maintained at approximately 21%
of air volume.
2. Removal of carbon dioxide
3. Control of humidity
 30 – 70% relative humidity (RH) is acceptable for
human comfort.
4. Prevention of heat concentrations from
machinery, lighting & people.

7. 5. Prevention of condensation
6. Dispersal of concentrations of bacteria
7. Dilution & disposal of contaminants
 Smoke, dust, gases & body odours
8. Provision of freshness
 An optimum air velocity lies between 0.15 & 0.5
m/s.

8.  Natural ……… mechanical
 It can be natural or mechanical ventilation.
 Natural ventilation
affected by
pressure variations due to
wind & stack effects.

9. Wind
 The movement of air takes place smoothly well
away from the earth’s surface.
 Velocity is reduced towards the ground,
direction of movement is affected by relief of
hills and mountains and vegetation resulting in
turbulence of airflow.
 Admiral Beaufort devised a scale in 1806
primarily for classification of winds at sea.

11. Typical Pattern of Pressure Distribution

12. In high buildings above ten floors, wind and
stack effect become apparent.

13. Stack Effect
 Natural movement of air within a tall building
caused by temperature difference between
outside and inside of building.
o Becomes stronger as the building gets
taller and the temperature difference
become greater.
 Stratification location: when light heated air
flows upward and reaches a point where it is
same temperature/weight as surrounding air.

15. The key requirement for ventilation is the
need to maintain adequate indoor air
quality.

16. An efficient ventilation system must meet
the following requirements:
1. Establish hazard-free air quality

17. 2. Satisfy user comfort

18. 3. Be energy efficient

19. 4. Be cost effective

20.  The air temperature and relative humidity
are major factors for maintaining comfort
and good health.
 Extreme conditions can cause discomfort,
promote the spread of microorganisms
which cause disease and can seriously
irritate the respiratory systems.

21. Ventilation Requirement
 Control of ventilation rates is influenced
by various authorities & codes of practice,
some statutory & other recommendations.

22. Recommended air change rate
Source : The society of Heating, Air Conditioning and Sanitary Engineers of Japan

23. The fresh air supply to a room can be calculated as :
Q = n V
where
Q = fresh air supply (ft3/h, m3/h)
n = air change rate (1/h)
V = volume of room (ft3, m3)

24. Q= nV
Example –
Fresh air supply to a public library with volume 1000m3
can be calculated as
Q = nV
Q=6x1000
=6000m3/h
Air change
rate

25. NATURAL VS MECHANICAL
Natural
Ventilation Mechanical
Ventilation

26. Natural Ventilation
 Depend on either:
 Wind direction & pressure,
or
 The stack effect of warm
air rising within a building,
while cooler air exists
outside.

27. Natural Ventilation
 The system involves the provision of
background ventilation for:
 periods of low occupancy, rapid ventilation for
temperature and air pollution during
occupancy, and the removal of local air
pollution at source rather than allowing it to
escape to the general atmosphere.
 e.g. cooking area or bathroom.
Cooking area Bathroom

28. Natural Ventilation
 uncontrolled windward and
outward leakage through
cracks and interstices (i.e.
infiltration and ex-filtration).
 The air entering and leaving the
enclosure through openings
provided intentionally e.g. open
windows and doors, and vents.
 Infiltration and ex-filtration are
caused by the weather and
other pressure-difference forces
exerted on a building.

29.  Infiltration Air is the unintentional and uncontrolled
entry of outdoor air into an enclosed space.
Infiltration occurs through cracks in the building
envelope and due to pressure differences between
inside and outside. The outdoor air entering through
open doors and windows is considered infiltration
although the purpose of opening the door or window
might be ventilation.
 Infiltration occurs mainly in winter when the air
outside is colder and heavier than the air inside. It
depends on wind velocity, wind direction and the air-
tightness of the building envelope. In the case of
high-rise buildings the stack effect also causes
infiltration

30.  Exfiltration Air refers to the flow of indoor air from an
enclosed building space to the outdoors.
 Commercial air-conditioned buildings are designed
to be air-tight (the windows cannot be opened)
and pressurized.
 In summer the air inside is colder (air-conditioned)
and therefore denser (heavier) than the hotter air
outside. The natural air flow direction is therefore
from inside to outside. Since commercial buildings
are pressurized, the air flow leakage is from the
inside to the outside.

32.  Traditional building materials
& traditional design are
suitable for the hot humid
climate in Malaysia.
 Due to competition for land and high demand
for houses, manufactured houses are built from
a new breed of building materials where
orientation and location followed the bare
minimum requirements of the by-laws.
 For high rise buildings, increase in use
of steel structures and glass render a
different set of problems e.g. glare,
green house effect etc.

33.  For natural ventilation, stack effect and wind
effects are dominant.
 Need to utilize windows, ventilators and air
spaces especially for night cooling.
 Windows should be narrow and keep (skinny)
with controllable openings at different levels.
Most houses are provided with side ventilation
and the air-well is often renovated such that it is
deemed useless for improving ventilation.

34. Mechanical Ventilation
 Ventilation provided by electric fans.
These fans are often part of an air-
conditioning system and may drive the
supply airflow, or both the supply and
exhaust airflows.

35. Mechanical ventilation or air-conditioning system is
suitable for
1. Internal rooms
2. Large closely populated rooms where distribution
of natural ventilation is inadequate
3. Rooms where volume per occupant is too low for
efficient natural ventilation.
4. Controlled environment e.g. clean room.
5. Windows cannot be opened either too noisy or
too dusty
6. Tall buildings for stack effect and smoke control
7. Extract ventilation e.g. fumes from processes.

36. In designing for high standards of air quality,
attention needs to be paid to a wide range
of building features.

37. Ventilation Standards
 ASHRAE (American Society of Heating,
Refrigeration and Air-Conditioning
Engineers) recommends for natural
ventilation, the air movement of 0.1 – 0.3
m/s (1.5 – 2.5 ach) for domestic, 1.5 – 2.5
ach for office, with air conditioner >3 ach.

39. Control of Air Quality and Ventilation

40. 1. Measurement
 It is very expensive to measure ventilation
rates to see whether specified standards
(refer to UBBL 1984) have been achieved.
One method is by using concentration
decay of a tracer gas e.g. SF6, NO2.
 Rate of decay (in concentration versus
time) gives the air change per hour.

42.  Age of air can be used to determine
ventilation effectiveness of a site.
 Another method uses a manometer where
it involves pressurizing the interior of a
building , with all windows and doors shut.
 A panel containing a fan and a measuring
equipment is sealed into the open front
door and a pressure of 55 Pa is maintained.
The procedure is repeated with negative
pressure. This method measures air
tightness.

43. 2. Air Movement
 Some degree of air movement is essential
for feeling of freshness and comfort.
 Desirable speeds vary with temperature
and conditions. In domestic buildings, a
velocity of 0.1 – 0.33 m/s is reasonable.
 In air-conditioned buildings, a velocity of 1
m/s is the norm except for clean room or
other localized extraction.

44. 3. Fumes, smells, product of combustion
 Where fumes are likely to be offensive or
injurious they should be removed by
extraction at source.
 Hoods or extractors should be placed to
capture fumes as soon as they are
emitted. Fume cupboards provide source
of fume to be enclosed.

45. 4. Bacteria
 Special precautions may be required in
hospitals or other places where bacterial
concentrations could be critical. Precautions
include no re-circulation of air, displacement
ventilation and high rates of air change.
 Patterns of air movement are such that
bacteria are swept away from areas they
may do harm, most critical at operating
theatres.

46. 5. Excess Heat
 Excess heat can be removed by
ventilation at sources (1 m3 can convey
1.3 kJ for each o C of temperature)
difference between the heated control
and the outside air.

47. 6. Relative Humidity
 Relative humidity of 30 – 70% is
acceptable. Increase ventilation rate can
reduce relative humidity; caution may get
too draughty.

48. Sick building syndrome
 Complaints of acute discomfort in office
building especially those equipped with air
conditioning.
 Ailments such as headache, eye ache, sore -
throat, breathing difficulty, cold – like
symptoms were real and clinically proven.
 When 20% of occupants or more complain of
these ailments then sick building syndrome
exists.

49.  Potential causes include:
 thermal, aural, visual, cleanliness, hygienic and
medical considerations. Common places include
swimming pool and recently refurbished building.
 Discrepancy between designed performance of
heating and air conditioning systems and actual
operations.
 Maintenance and regular housekeeping is
important to ensure effectiveness of a system.
 Sick building complaints have been reduced by a
rigorous process of cleaning.
 There is a need for minimum standards of
installation, commissioning and operation of
environmental systems to be established and
incorporated into building contracts and
legislation.

50. Flow caused by wind
Major factors affecting ventilation wind forces include:
 average wind speed;
 prevailing wind direction;
 seasonal and daily variation in wind speed and
direction;
 local obstructing objects, such as nearby buildings and
trees;
 position and characteristics of openings through which
air flows; and
 distribution of surface pressure coefficients for the wind.
 Natural ventilation systems are often designed for wind
speeds of half the average seasonal velocity because
from climatic analysis there are very few places where
wind speed falls below half the average velocity for
many hours in a year.

51. TUTORIAL TASK:
 BY REFER TO UBBL 1984, STUDENTS ARE REQUIRED TO
HIGHLIGHT THE VENTILATION REQUIREMENTS IN A
BUILDING. (CLAUSES RELATED SHOULD BE STATED)

52. THANK YOU