type of ventilation factors effecting and type of ventilation

1. BUILDING SCIENCE
MODULE 2
VENTILATION
SUHAS H B, DEPARTMENT OF CTM, DSCE
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31-Jan-20

2. VENTILATION
 Ventilation is the process of supplying fresh air
from outside into a room and removing used air
from inside the room.
 Creating air movement which improves the
comfort of occupants.
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3. NECESSITY OF VENTILATION.
 To have continuous movement of air inside the room.
 To remove excess carbon dioxide.
 To prevent the accumulation of dust and bacteria inside
the room.
 To remove odour.
 To remove body heat of the occupant.
 To prevent the condensation in the buildings.
 To prevent suffocation inside the closed space. 3
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4. FACTORS AFFECTING VENTILATION.
 Air changes.
 Purity of air.
 Air temperature.
 Humidity.
 Use of buildings.
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5. REQUIREMENT OF A GOOD
VENTILATION SYSTEM.
 It should be designed that the required quantity of fresh air
is admitted in the premises and that the impure air is
extracted.
 The value of relative humidity is maintained.
 The effective temperature should be properly maintained
with regard to the human comfort.
 The air movement should be uniform and it should be seen
that pockets of stagnant air are not formed.
 The incoming air should be free from impurities such as
dust, odour etc. 5
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6. HEALTH VENTILATION
 The quality of air in buildings is maintained above
a certain minimum level by indoor air buy fresh
outdoor air to maintain certain level of carbon
dioxide and oxygen in air for control of odour or
for removal of products of combustion during
Occupancy. Ventilation to meet this requirement
essentially needed under all climatic condition.
Hence it is termed as health ventilation.
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7. COMFORT VENTILATION.
 Condition necessitates ventilation for providing
such thermal environment due to increasing heat
loss from the body and prevent discomfort due to
moist skin and also to cool the indoor space itself
when the Indore temperature exceeds outdoor
temperature. This type of ventilation is termed as
comfort ventilation.
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8. TYPES OF VENTILATION.
 Natural ventilation.
 Artificial/Mechanical ventilation.
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9. NATURAL VENTILATION.
 Supply of outside air into a building through window
or other openings due to Convection effects
arising from temperature and vapour pressure
differences (or both) between inside and outside of
the building.
 This system is generally used in small residential
buildings, small office and other small buildings.
 This system is economical since no other
equipment are used for the ventilation.
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10. POINTS MUST BE CONSIDERED WHILE
PROVIDING NATURAL VENTILATION.
 Doors and windows must be properly located to
provide maximum flow of air.
 The height of the room should be sufficient.
 The opening should not be obstructed.
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11. EFFECTS ARE PREDOMINANT DURING NATURAL
VENTILATION.
 Stack effect
 Wind effect
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12. STACK EFFECT.
 This effect mainly due to the
temperature & vapour pressure
differences.
 As soon as the inside temperature get
warmer and less denser air will move
upwards and try to pass through the
openings near the roof level and at the
same time cooler and heavier air tries
to enter into the room from outside the
building through the inlet openings
provided at the floor level. This is
called conviction stack effect.
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13.  Rate of ventilation due to stack effect is given by
Q = 640Ce A h (Tr - to)
Where,
Q = Rate of flow of air, m3/hour.
Ce = Co-efficient of effectiveness (Ce =0.65)
A = Effective area of inlet, m2
H = Height difference between inlet and
outlet, m
Tr = Average temperature, ºC.
to = Outside temperature, ºC.
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14. WIND EFFECT.
 This effect takes place when a building
has sufficient movement of air around
the building.
 When the air moves it carries some
momentum. When the moving air strikes
a building it apply some pressure. When
that pressure acts on the openings, the
wind created positive pressure which
initiates the movement of air inside the
room. When this air enters the room,
automatically the used air moves out due
to the pressure. 14
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15.  Wind effect is more when the outlet openings are very close to the
floor level. Ventilation is affected by direction and velocity of wind
and position of the opening. Wind creates pressure, pressure create
suction which helps the process of ventilation.
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16. The rate of flow of air in natural ventilation is determined by the
following formula.
Q = KAV
Where,
Q = Rate of flow of air, m3/hour.
K = Coefficient of flow which may be taken as 0.6 for
wind perpendicular to the openings and 0.3 for winds
incident at 45º.
V = prevailing outdoor wind speed in m/h.
A = Area of openings provided on wall in m2.
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17. MECHANICAL VENTILATION.
 Supply of outside air either way positive ventilation or by
positive infiltration by reduction of pressure inside due to
exhaust of air or by combination of both positive
ventilation and exhaust of air.
 Methods of artificial ventilation.
1. By providing exhaust fans.
2. By supply of fresh air from outside.
3. Exhaust and supply system.
4. Air conditioning.
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18. EXHAUST FANS.
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19. SUPPLY SYSTEM.
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20. EXHAUST AND SUPPLY SYSTEM.
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