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Copyright © Wondershare Software1
Principles of Architectural and Environmental Design
EARC 2417
Islamic University-Gaza
Faculty of Engineering
Architectural Department
Instructor: Dr. Suheir Ammar
2019
Lecture 11Natural Ventilation
(Passive Cooling)
Copyright © Wondershare Software2
Natural Ventilation
(Passive Cooling)
1. Principles of Natural Ventilation NV
1.1 Understanding air flow
1.2 Stack effect
1.3 Wind effect
2. Ventilation in Interior Spaces
2.1 Ventilation Concepts in Interior Spaces
2.2 Window placement
2.3 Interior partitions
3. Vegetation and ventilation
Copyright © Wondershare Software3
Natural Ventilation (Passive Cooling)
Natural ventilation is necessary for:
Fresh air supply into the building,
Increasing, through air movement, the rate of
perspiration evaporation from the bodies of those in
the building,
Cooling the interior of the building by exchanging
relatively warm hot internal air with cooler outside air
1. Principles of Natural VentilationFor air to move into and out of a building, a pressure
difference between the inside and outside of the
building is required.
The pressure difference is caused by:
• wind (or wind effect)
• difference in air density due to temperature difference
between indoor and outdoor air (stack or chimney effect)
• combination of both wind and stack effects.
1. Principles of NV
1.1 Understanding air flow
1.2 Stack effect
1.3 Wind effect
2. Ventilation in Interior
Spaces
2.1 Ventilation Concepts in
Interior Spaces
2.2 Window placement
2.3 Interior partitions
3. Vegetation & Ventilation
Copyright © Wondershare Software4
1.1. Understanding air flow
1. Principles of NV
1.1 Understanding air flow
1.2 Stack effect
1.3 Wind effect
2. Ventilation in Interior
Spaces
2.1 Ventilation Concepts in
Interior Spaces
2.2 Window placement
2.3 Interior partitions
3. Vegetation & Ventilation
Principle 1: Air will always flow from region of high
pressure to lower pressure
low pressurehigh pressure
barrier
Principle 2: Air has mass and it will tend to continue
in its direction until altered by an barrier or an
adjacent air flow.
Copyright © Wondershare Software5
1.1. Understanding air flow
Principle 3: The overall effect of wind at a site is so
large that locally deflected airflow (by trees or
buildings) will tend to return to the direction and speed
of the site wind.
1. Principles of NV
1.1 Understanding air flow
1.2 Stack effect
1.3 Wind effect
2. Ventilation in Interior
Spaces
2.1 Ventilation Concepts in
Interior Spaces
2.2 Window placement
2.3 Interior partitions
3. Vegetation & Ventilation
Copyright © Wondershare Software
1
2
1.1. Understanding air flow
Principle 4: Airflow is smooth with adjacent air moving
in similar direction and speed.
1. Slow, gentle alterations of flow direction will preserve
laminar* flow,
2. Sudden alterations results in “turbulent flow” whereby
adjacent air currents separate suddenly into swirling,
unpredictable directions.
3. When two currents of air traveling in opposite
directions, they will always be separated by eddies
because adjacent particles of air always move in the
same direction.
1. Principles of NV
1.1 Understanding air flow
1.2 Stack effect
1.3 Wind effect
2. Ventilation in Interior
Spaces
2.1 Ventilation Concepts in
Interior Spaces
2.2 Window placement
2.3 Interior partitions
3. Vegetation & Ventilation
3
Copyright © Wondershare Software7
Principle 5: when laminar airflow is constricted in
order to pass through an opening, the same volume
of air must pass through a smaller area, so it causes
an acceleration of air flow.
1.1. Understanding air flow
1. Principles of NV
1.1 Understanding air flow
1.2 Stack effect
1.3 Wind effect
2. Ventilation in Interior
Spaces
2.1 Ventilation Concepts in
Interior Spaces
2.2 Window placement
2.3 Interior partitions
3. Vegetation & Ventilation
an acceleration air flow
windows
Copyright © Wondershare Software8
Principle 6: Cross-ventilation requires an outlet as well
as an inlet.
1. Principles of NV
1.1 Understanding air flow
1.2 Stack effect
1.3 Wind effect
2. Ventilation in Interior
Spaces
2.1 Ventilation Concepts in
Interior Spaces
2.2 Window placement
2.3 Interior partitions
3. Vegetation & Ventilation
1.1. Understanding air flow
Analogy: water cannot be
put into a bottle that
already full unless some
old water is removed first.
Copyright © Wondershare Software
1.1. Understanding air flow
9
Principle 7: The stack effect
Stack effect is the result of air density decreasing
as temperature increase.
Warm air rises through upper openings and
replaced by cooler through low openings.
1. Principles of NV
1.1 Understanding air flow
1.2 Stack effect
1.3 Wind effect
2. Ventilation in Interior
Spaces
2.1 Ventilation Concepts in
Interior Spaces
2.2 Window placement
2.3 Interior partitions
3. Vegetation & Ventilation
The stack effect
Copyright © Wondershare Software10
1.2. Stack effect
Stack effect is the result of air density decreasing
as temperature increase.
Warm air rises through upper openings and
replaced by cooler through low openings.
If the wind shifts, the air circulation may reverse,
causing the solar-heated air to be blown down
into the living space, effectively heating the
building rather than cooling it. For this reason,
any solar chimney should have a wind-activated
ventilator cap to ensure that airflow is always
positive.
1. Principles of NV
1.1 Understanding air flow
1.2 Stack effect
1.3 Wind effect
2. Ventilation in Interior
Spaces
2.1 Ventilation Concepts in
Interior Spaces
2.2 Window placement
2.3 Interior partitions
3. Vegetation & Ventilation
heated air to be blown down Warm air rises
Copyright © Wondershare Software
The Wind effect
1.1. Understanding air flow1. Principles of NV
1.1 Understanding air flow
1.2 Stack effect
1.3 Wind effect
2. Ventilation in Interior
Spaces
2.1 Ventilation Concepts in
Interior Spaces
2.2 Window placement
2.3 Interior partitions
3. Vegetation & Ventilation
Copyright © Wondershare Software12
1.3. Wind effect
When air flow is due to wind, air
enters through openings in the
windward walls, and leaves
through openings in the leeward
walls.
Wind pressures are generally
high/positive on the windward
side of a building and low/
negative on the leeward side.
1. Principles of NV
1.1 Understanding air flow
1.2 Stack effect
1.3 Wind effect
2. Ventilation in Interior
Spaces
2.1 Ventilation Concepts in
Interior Spaces
2.2 Window placement
2.3 Interior partitions
3. Vegetation & Ventilation
The occurrence and change of wind pressures on building surfaces depend on:
wind speed and wind direction relative to the
building.
the location and surrounding environment of the
building.
shape of the building.
Copyright © Wondershare Software13
Low pressure zones occur along the
sides parallel to the wind and on the
leeward side of the building.
1.3. Wind effect
1. Principles of NV
1.1 Understanding air flow
1.2 Stack effect
1.3 Wind effect
2. Ventilation in Interior
Spaces
2.1 Ventilation Concepts in
Interior Spaces
2.2 Window placement
2.3 Interior partitions
3. Vegetation & Ventilation
The following diagrams describe principles of
ventilation airflow around buildings and the pressure
distribution patterns due to wind.
Plan
Copyright © Wondershare Software14
A low building
placed in the
windward path of a
tall building produce
a large amount
turbulence
“instability” between
the two buildings.
An opening on
windward side only
results in poor
ventilation.
1.3. Wind effect
1. Principles of NV
1.1 Understanding air flow
1.2 Stack effect
1.3 Wind effect
2. Ventilation in Interior
Spaces
2.1 Ventilation Concepts in
Interior Spaces
2.2 Window placement
2.3 Interior partitions
3. Vegetation & Ventilation
Copyright © Wondershare Software15
Raising a tall building
reduce the high
pressure on the
windward side by
allowing airflow under
the building.
1.3. Wind effect
1. Principles of NV
1.1 Understanding air flow
1.2 Stack effect
1.3 Wind effect
2. Ventilation in Interior
Spaces
2.1 Ventilation Concepts in
Interior Spaces
2.2 Window placement
2.3 Interior partitions
3. Vegetation & Ventilation
Copyright © Wondershare Software
Airflow patterns through a) a normal, b) a scattered
c) a diagonal layout of buildings.
1. Principles of NV
1.1 Understanding air flow
1.2 Stack effect
1.3 Wind effect
2. Ventilation in Interior
Spaces
2.1 Ventilation Concepts in
Interior Spaces
2.2 Window placement
2.3 Interior partitions
3. Vegetation & Ventilation
Wind & building arrangement³
Staggered building
arrangements result
in reduced wind
shadows.
Copyright © Wondershare Software17
2.1 Ventilation Concepts in Interior Spaces
Single Sided Ventilation:
This kind of ventilation is normal
and generally practiced, but it is
only useful up to a certain room
depth
Cross Ventilation:
In order to obtain the optimal
airflow with minimal draught,
the windows on the
windward side are opened
less than on the lee side.
Single Sided Double
Opening:
An advancement of the single
sided principle provides a
double opening, which is
considerably more efficient.
2. Ventilation in Interior Spaces
1. Principles of NV
1.1 Understanding air flow
1.2 Stack effect
1.3 Wind effect
2. Ventilation in Interior
Spaces
2.1 Ventilation Concepts in
Interior Spaces
2.2 Window placement
2.3 Interior partitions
3. Vegetation & Ventilation
Copyright © Wondershare Software18
Passive Cooling:
As the external temperature drops at night, the building
can be cooled by partially opening the vents around the
building - often called night-cooling.
1. Principles of NV
1.1 Understanding air flow
1.2 Stack effect
1.3 Wind effect
2. Ventilation in Interior
Spaces
2.1 Ventilation Concepts in
Interior Spaces
2.2 Window placement
2.3 Interior partitions
3. Vegetation & Ventilation
2.1 Ventilation Concepts in Interior Spaces
night-cooling
Copyright © Wondershare Software19
1. Principles of NV
1.1 Understanding air flow
1.2 Stack effect
1.3 Wind effect
2. Ventilation in Interior
Spaces
2.1 Ventilation Concepts in
Interior Spaces
2.2 Window placement
2.3 Interior partitions
3. Vegetation & Ventilation
2.1 Ventilation Concepts in Interior Spaces
Copyright © Wondershare Software20
1. Principles of NV
1.1 Understanding air flow
1.2 Stack effect
1.3 Wind effect
2. Ventilation in Interior
Spaces
2.1 Ventilation Concepts in
Interior Spaces
2.2 Window placement
2.3 Interior partitions
3. Vegetation & Ventilation
2.1 Ventilation Concepts in Interior Spaces
A solar chimney uses the
sun's heat to provide
cooling, using the stack
effect. Solar heat gain
warms a column of air,
which then rises, pulling
new outside air through the
building.
Solar chimneys can also be
used for heating. If the top
exterior vents are closed,
the heated air is not
exhausted out the top; at the
same time, if high interior
vents are opened to let the
heated air into occupied
spaces, it will provide
convective air heating
Copyright © Wondershare Software21
1. Principles of NV
1.1 Understanding air flow
1.2 Stack effect
1.3 Wind effect
2. Ventilation in Interior
Spaces
2.1 Ventilation Concepts in
Interior Spaces
2.2 Window placement
2.3 Interior partitions
3. Vegetation & Ventilation
2.1 Ventilation Concepts in Interior Spaces
Solar chimney in buildings
Copyright © Wondershare Software
1. On opposite walls in rooms, cross-ventilation creates the best airflow.
2. On adjacent walls in a room, cross-ventilation can be improved by positioning of wing walls adjacent to the window openings.
3. On one exterior wall in a room, with only wing walls adjacent to window have been found to increase ventilation.
22
1. Principles of NV
1.1 Understanding air flow
1.2 Stack effect
1.3 Wind effect
2. Ventilation in Interior
Spaces
2.1 Ventilation Concepts in
Interior Spaces
2.2 Window placement
2.3 Interior partitions
3. Vegetation & Ventilation
2.2. Window placement
Copyright © Wondershare Software23
1. Principles of NV
1.1 Understanding air flow
1.2 Stack effect
1.3 Wind effect
2. Ventilation in Interior
Spaces
2.1 Ventilation Concepts in
Interior Spaces
2.2 Window placement
2.3 Interior partitions
3. Vegetation & Ventilation
2.2. Window placement³
Air flow patterns around a
building and impact of
opening location on
ventilation
Copyright © Wondershare Software24
wing wall design
patterns for two
windows on the
same or adjacent
walls
showing probable
airflow patterns and
wind directions for
improved ventilation
performance
due to wing walls:
1. Principles of NV
1.1 Understanding air flow
1.2 Stack effect
1.3 Wind effect
2. Ventilation in Interior
Spaces
2.1 Ventilation Concepts in
Interior Spaces
2.2 Window placement
2.3 Interior partitions
3. Vegetation & Ventilation
2.2. Window placement “on the same or adjacent walls“
excellent
good poor
poor poor
goodexcellent
good
Copyright © Wondershare Software25
2.2. Window placement
1. Principles of NV
1.1 Understanding air flow
1.2 Stack effect
1.3 Wind effect
2. Ventilation in Interior
Spaces
2.1 Ventilation Concepts in
Interior Spaces
2.2 Window placement
2.3 Interior partitions
3. Vegetation & Ventilation
lf the inlet is larger than the outlet, velocity in the room is
reduced (although velocity outside just to-leeward of the
outlet is increased). This has potential for cooling a
localized exterior area such as a patio
Maximum air exchange is created when the
inlet and outlet areas are equal, making the
optimum configuration when building cooling is
the goals.
cooling an
exterior area
“a patio”
1 2
Maximum air exchange
Copyright © Wondershare Software26
2.2. Window placement
1. Principles of NV
1.1 Understanding air flow
1.2 Stack effect
1.3 Wind effect
2. Ventilation in Interior
Spaces
2.1 Ventilation Concepts in
Interior Spaces
2.2 Window placement
2.3 Interior partitions
3. Vegetation & VentilationMaximum interior air speed is created when the inlet
is smaller than the outlet, making the optimum
configuration when people cooling is the goal.
3
Maximum interior air speed
Copyright © Wondershare Software27
2.2. Window placement
1. Principles of NV
1.1 Understanding air flow
1.2 Stack effect
1.3 Wind effect
2. Ventilation in Interior
Spaces
2.1 Ventilation Concepts in
Interior Spaces
2.2 Window placement
2.3 Interior partitions
3. Vegetation & Ventilation
A baffle (wing wall, door, or casement window) placed
perpendicular to the opening changes the direction of
airflow through the space with only a small reduction in
velocity.
a small reduction
in velocity.
Copyright © Wondershare Software28
An inlet centered in the wall restricts airflow to a side
outlet due to an abrupt change in direction, flow is
increased by repositioning the inlet to a more diagonal
location and adding a baffle directs entering air
diagonally in the direction of the outlet.
2.2. Window placement
1. Principles of NV
1.1 Understanding air flow
1.2 Stack effect
1.3 Wind effect
2. Ventilation in Interior
Spaces
2.1 Ventilation Concepts in
Interior Spaces
2.2 Window placement
2.3 Interior partitions
3. Vegetation & Ventilation
Copyright © Wondershare Software29
2.2. Window placement
1. Principles of NV
1.1 Understanding air flow
1.2 Stack effect
1.3 Wind effect
2. Ventilation in Interior
Spaces
2.1 Ventilation Concepts in
Interior Spaces
2.2 Window placement
2.3 Interior partitions
3. Vegetation & Ventilation
Openings located at the corner of the building allow the
inertia to continue the motion in the same direction in a
smooth curve until the outlet is reached.
Copyright © Wondershare Software30
2.2. Window placement
1. Principles of NV
1.1 Understanding air flow
1.2 Stack effect
1.3 Wind effect
2. Ventilation in Interior
Spaces
2.1 Ventilation Concepts in
Interior Spaces
2.2 Window placement
2.3 Interior partitions
3. Vegetation & Ventilation
The vertical position of the inlet window is
important in maximizing the airflow through the
lower, occupied portion of the room.
The outlet location has little effect on flow within
the room
The low inlet is better for cooling.
Copyright © Wondershare Software31
2.2. Window placement
1. Principles of NV
1.1 Understanding air flow
1.2 Stack effect
1.3 Wind effect
2. Ventilation in Interior
Spaces
2.1 Ventilation Concepts in
Interior Spaces
2.2 Window placement
2.3 Interior partitions
3. Vegetation & Ventilation The addition of a slot separating the overhang
from the building redirects the flow down into the
room, increasing the useful cooling effect .
An overhang above the inlet window
directs the interior airflow along the ceiling
out of the occupied zone.
Copyright © Wondershare Software32
An overhang or an awning increases air
velocity through a window below them
Sashes configuration may have a significant
effect on the flow of air through an opening.
2.2. Window placement
1. Principles of NV
1.1 Understanding air flow
1.2 Stack effect
1.3 Wind effect
2. Ventilation in Interior
Spaces
2.1 Ventilation Concepts in
Interior Spaces
2.2 Window placement
2.3 Interior partitions
3. Vegetation & Ventilation
Effect of sashes
Copyright © Wondershare Software33
2.3 Interior partitions
The location and orientation of interior partitions can
affect the velocity and direction.
1. Principles of NV
1.1 Understanding air flow
1.2 Stack effect
1.3 Wind effect
2. Ventilation in Interior
Spaces
2.1 Ventilation Concepts in
Interior Spaces
2.2 Window placement
2.3 Interior partitions
3. Vegetation & Ventilation
The partition placed
perpendicular to the
direction of airflow redirects
the pattern and reduces the
velocity.
The partition placed
parallel to the direction
of airflow have least
effect.
Copyright © Wondershare Software34
2.3 Interior partitions
1. Principles of NV
1.1 Understanding air flow
1.2 Stack effect
1.3 Wind effect
2. Ventilation in Interior
Spaces
2.1 Ventilation Concepts in
Interior Spaces
2.2 Window placement
2.3 Interior partitions
3. Vegetation & Ventilation
Partitions placed blocking
the path create a “barrier”
effect, creating motionless
areas.
Partitions placed outside
of the main airflow path
have little effect.
Copyright © Wondershare Software35
3. Vegetation and ventilation
Vegetation increasing, decreasing and directing airflow
1. Principles of NV
1.1 Understanding air flow
1.2 Stack effect
1.3 Wind effect
2. Ventilation in Interior
Spaces
2.1 Ventilation Concepts in
Interior Spaces
2.2 Window placement
2.3 Interior partitions
3. Vegetation & VentilationVegetation causes pressure
differences which shifts the
air path
Copyright © Wondershare Software
3. Vegetation and ventilation2
36
1. Principles of NV
1.1 Understanding air flow
1.2 Stack effect
1.3 Wind effect
2. Ventilation in Interior
Spaces
2.1 Ventilation Concepts in
Interior Spaces
2.2 Window placement
2.3 Interior partitions
3. Vegetation & Ventilation good ventilation poor ventilation
Copyright © Wondershare Software
3. Vegetation and ventilation 2
37
Copyright © Wondershare Software38
3. Vegetation and ventilation
1. Principles of NV
1.1 Understanding air flow
1.2 Stack effect
1.3 Wind effect
2. Ventilation in Interior
Spaces
2.1 Ventilation Concepts in
Interior Spaces
2.2 Window placement
2.3 Interior partitions
3. Vegetation & Ventilation Effect on ventilation of a low hedge (less than 3 ft high)
located parallel to the windward windows at different
distances.
Copyright © Wondershare Software39
3. Vegetation and ventilation
1. Principles of NV
1.1 Understanding air flow
1.2 Stack effect
1.3 Wind effect
2. Ventilation in Interior
Spaces
2.1 Ventilation Concepts in
Interior Spaces
2.2 Window placement
2.3 Interior partitions
3. Vegetation & Ventilation
Effect on ventilation of a medium hedge located
parallel to the windward windows at different distances.
Copyright © Wondershare Software40
3. Vegetation and ventilation
1. Principles of NV
1.1 Understanding air flow
1.2 Stack effect
1.3 Wind effect
2. Ventilation in Interior
Spaces
2.1 Ventilation Concepts in
Interior Spaces
2.2 Window placement
2.3 Interior partitions
3. Vegetation & Ventilation
Effect on ventilation of a high hedge located
parallel to the windward windows at different
distances.
Copyright © Wondershare Software41
3. Vegetation and ventilation
1. Principles of NV
1.1 Understanding air flow
1.2 Stack effect
1.3 Wind effect
2. Ventilation in Interior
Spaces
2.1 Ventilation Concepts in
Interior Spaces
2.2 Window placement
2.3 Interior partitions
3. Vegetation & Ventilation
Effect on ventilation
of a 30-ft tree on
the windward sides
at different
distances.
Copyright © Wondershare Software42
Thank you
Reference:
1. Moore, Fuller, 1993. Environmental control systems: heating, cooling,
lighting. New York : McGraw-Hill
2. Santamouris, M., Allard, F., Energy, E. C. D.-G. f., & Programme, A.
(1998). Natural Ventilation in Buildings: A Design Handbook: James and
James (Science Publishers) Limited
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