VENTILATION
National Building Code Of India
Part 8 Building Services
Section 1 Lighting and Ventilation
Submitted By : Submitted To :
Tanam Swarup Mahajan Ms. Surabhi
17BT010159 Assistant Professor
Civil, 4th Sem. Dept. of Civil
Ventilation
Circulation of air in the Building or is the change of air in room.
For living fresh air is necessary for a house.
Importance & Purpose of Ventilation :
Proper ventilation prevent air pollutant from affecting the health of
people live in the building.
Maintain Quantity of air inside the building at certain level.
Supply of fresh air for breathing.
Maintain the heat balance of the body.
Cool the structure of building when the inside temperature is
above outdoor.
Recommended values for Air Changes
Methods of Ventilation
Natural Supply and Natural Exhaust of Air
Natural Supply and Mechanical Exhaust of Air
Mechanical Supply and Natural Exhaust of Air
Mechanical Supply and Mechanical Exhaust of Air
Natural Ventilation
The rate of ventilation by natural means through windows or
other openings depends on :
Direction and velocity of wind outside and sizes and
disposition of openings.
Convection effects arising from temperature of vapour
pressure difference between inside or outside the room
and the difference of height between the outlet and inlet
openings (Stack Effect).
Basic Guidelines for Natural Ventilation
Vent opening properly distributed. Inlet should be located in
windward side at low level and outward opening should be on
the leeward side at a higher level near roof.
Outlet openings on shorter side and inlets on longer side of
rooms provide better ventilation.
Openings should not have obstructions like trees, buildings,
signboards etc.
Cross ventilation (providing openings in opposite walls) helps
in more air changes. But can lead to air stagnation pockets
and air circulation is restricted only to a limited portion.
Height of a room should be proportionate to its size, number
of users, nature of activity etc.
Provision for exit of smoke and fumes should be on roof.
Area of inlet openings should not be less than
• 1/10th of floor area of residential building
• 1/8th of buildings such as offices, schools, colleges,
hospitals, etc.
There must be atleast one window or ventilator in every
room.
Inlet must be free from any obstruction.
Outlet openings should be provided near roof on leeward
side
Stack Effect
Stack effect or chimney effect is the movement of
air into and out of buildings, chimneys, flue-gas
stacks, or other containers, resulting from air
buoyancy. Buoyancy occurs due to a difference in
indoor-to-outdoor air density resulting from
temperature and moisture differences.
Determining rate of Ventilation
Wind action : For determining the rate of ventilation based
on wind action the wind may be assumed to come from any
direction within 45° of the direction of prevailing wind.
Ventilation due to external wind is given by the following
formula:
Q=KAV
Here, Q = Rate of air flow in m3/h
K = Coefficient of effectiveness, which maybe taken as
0.6 for wind perpendicular to openings and 0.3 for wind at an
angle less than 45° to the openings
A = Free area of inlet openings in m2
V = Wind speed in n/h.
Stack effect : Ventilation due to convection effects arising
from temperature difference between inside and outside is
given by :-
Q = 7A√ℎ(𝑇𝑡 − 𝑇0)
Here, Q = Rate of air flow in m3/h
A = Free area of inlet openings in m2
h = Vertical distance between inlets and outlets in m
Tt = Average temperature of indoor air at height h in 0C.
T0 = Temperature of outdoor air in 0C.
Mechanical Ventilation
Fresh air supplied to the building wither by :-
• Positive ventilation : supply of fresh air means by
mechanical device such as fan or blower
• By infiltration by reduction of pressure inside due to
exhaust of air: ventilated air exhausted by providing exhaust
fans near ceiling of roof
• By a combination of two
Energy Conservation in Ventilation System
Maximum possible use should be made of wind induced natural ventilation.
Adequate number of circulating fans should be installed to serve all interior working areas
during summer months in the hot dry and warm humid regions to provide necessary air
movement at times when ventilation due to wind action alone does not afford sufficient
relief.
The capacity of a ceiling fan to meet the requirement of a room with the longer dimension
D m should be about 55D m3/min.
The height of fan blades above the floor should be (3H + W)/4, where H is the height of the
room, and W is the height of work plane.
The minimum distance between fan blades and the ceiling should be about 0.3 m
Electronic regulators should be used instead of resistance type regulators for controlling
the speed of fans.
When actual ventilated zone does not cover the entire room area, then optimum size of
ceiling fan should be chosen based on the actual usable area of room, rather than the total
floor area of the room. Thus smaller size of fan can be employed and energy saving could
be achieved.
Power consumption by larger fans is obviously higher, but their power consumption
per square metre of floor area is less and service value higher. Evidently, improper
use of fans irrespective of the rooms dimensions is likely to result in higher power
consumption. From the point of view of energy consumption, the number of fans
and the optimum sizes for rooms of different dimensions are given in Table
