Transcript folu presentation AR..

VENTILATION
AIR FLOW THROUGH BUILDINGS
BUILDING CLIMATOLOGY
ARC 810
Department Of Architecture,
Federal University of Technology Akure, Nigeria
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Sub - topics
 Introduction
 Basic Concept in Ventilation
 Air flow through Buildings
 Factors Affecting Air flow through Buildings
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Introduction
Ventilation is the replacement of used inside air by
outside air . It has three major functions
 Supply of fresh air
 Body cooling
 Structural cooling or heating
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Introduction
Ventilation in buildings can be achieved by
 the stack effect due to difference in temperature
between the air within and outside the building.
 air movement induced by wind pressure.
 mechanical means.
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Introduction
Factors affecting air flow through buildings
 External features and factors
 Number and size of openings
 Position of openings
 Opening Component
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Introduction
 Ventilation is predicted by mathematical
formulae or with the aid of models.
 Air flow around buildings  Orientation
is determined by
 Shape
 Height
 Planning of Buildings
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Basic Concept in Ventilation
 Cross ventilation is ventilation achieved by placing
openings in opposite walls of an enclosure.
 Natural ventilation is ventilation achieved without
mechanical aids, but by stack effect and wind
pressure.
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Basic Concept in Ventilation
 Comfort cooling is the use of air movement for
body cooling.
 Infiltration is uncontrolled air flow into or through a
building especially via gaps in doors and windows.
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Basic Concept in Ventilation
 Air movement refers to the circulation of air
within a space and is not necessarily associated
with ventilation.
 Ventilation is measured in air changes per hour.
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Ventilation Function and
Requirements
Function
Fresh Air
Body cooling
Required
Suitable building
in all occupied
buildings
all buildings
in warm humid
conditions
single banked building
Adequacy of method
-stack effect
-wind pressure
-mechanical`
adequate
adequate
not necessary
not adequate
good if available
may be desirable
1
100
Required change per hour
Structural
Cooling
In hot dry
conditions
High
internal
Heat
capacity
Adequate
Adequate
Not
necessary
10
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Function of Ventilation
Supply of fresh air
This removes carbon dioxide, odours,
vapours, gases from cooking and tobacco
smoke by replacing used internal air by
external air .
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Function of Ventilation
Body cooling
This is achieved through the evaporation of sweat
from the skin and increased heat loss from the skin
by forced convection. The cooling is achieved by air
velocity and not by low temperature.
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Function of ventilation
Structural cooling and heating
To cool the building, the cool air from outside is drawn
into the warm interior where it lowers the air
temperature and cools the building. The reverse is the
case when the building interior needs to be heated up.
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Air flow through Buildings
Air movement through buildings can be induced
by
The stack Effect
Wind Pressure
Mechanical means
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Air flow through Buildings
by
Stack effect
This refers to the movement of air as a
result of differences in air pressure of two
bodies of air at different temperatures.
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Stack Effect continued
The rate of ventilation
achieved is directly
proportional to the area of
the inlet, and the square
root of the difference in
temperature between
inside and outside air, and
the difference in height
between the inlet an
outlet.
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Stack Effect continued
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Stack Effect continued
 Ventilation rate increases with increase in the
ratio of the area of the outlet to that of the
inlet
This ratio determines the correction factor
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Stack Effect continued
Correction factors for ventilation rate in relation to
inlet and outlet size
Ao/Ai
5
4
3
2
1
0.75
0.50
0.25
K
0.161
0.160
0.156
0.147
0.117
0.098
0.074
0.040
Where
A o = area of outlet
Ai = area of inlet
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Stack Effect continued
 Stack effect cannot be relied upon to provide
adequate cooling by air movement in warm humid
conditions, even with large windows due to the
low difference in temperature between the inside
and the outside.
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Stack Effect continued
 Stack effect can provide structural cooling at
night time in hot dry climates, especially during
the hot season.
 The cooling produced by stack effect can be
increased by better design of openings.
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Stack Effect continued
 Inlets should be on the windward side of
buildings with outlets on the leeward side.
 The difference in height between inlet and
outlet should be maximized.
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Air flow through Buildings
by
Wind pressure
The aim of design is usually to maximize wind
pressure for air movement. Wind pressure and
stack effect often act together to create air
within buildings
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Wind Pressure continued
When the wind strikes a building it
is slowed down but at the same
time it exerts a pressure on the
building. The pressure exerted is
directly proportional to the square
of the wind velocity.
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Wind Pressure continued
 The slowed down wind forms a mass on the
windward face of the building and on other
surfaces of the building at reduced pressure
resulting in suction
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Wind Pressure continued
The wind is deflected above and around this
mass and travels some distance before it regains
its direction due to its tendency to maintain a
straight path (momentum)
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Wind Pressure continued
The combined effect of
pressure on the windward side
and suction the leeward side is
to encourage air flow through
the building.
Wind pressure and suction on buildings
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Air Flow through Buildings
by
Mechanical means
The use of mechanical aids is usually employed
only if the air movement induced by wind
pressure or stack effect is insufficient.
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Mechanical means
continued
These mechanical aids are
 fans
 evaporative coolers
 air conditioners
 heaters.
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Mechanical means
continued
These aids provide
air movement
humidification or dehumidification
cooling
heating
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Mechanical means
continued
Fans
Electric fans are useful in providing
necessary air movement for body cooling,
especially in the warm humid climates in
the southern part of the country.
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Mechanical means
continued
Types of electric fans
standing fans
extract fans
ceiling fans
wall mounted fans
table fans
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Mechanical means
continued
Extract fans
•cannot be used for body cooling because they do
not blow air;
•they may be used to assist the stack effect and
remove odours and vapours.
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Mechanical means
continued
Evaporative Coolers
the wind scoop
the desert cooler
They are used for both cooling and humidification
especially in hot dry climates .
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Mechanical means
continued
Principle of the Evaporative coolers
As water evaporates from the atmosphere it
absorbs heat and in turn lowers the temperature
at the same time the evaporated water increases
the relative humidity of the air, causing humidification
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Mechanical means
continued
The wind scoop catches the
wind with the aid of
properly oriented shafts
projecting above roof level.
The wind is channeled
through charcoal wetted by
earthenware pots.
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Mechanical means
continued
The desert cooler has an electric
fan blowing air through a wet
fabric kept damp by a small
pump feeding on a reservoir.
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Mechanical means
continued
Air Conditioners
they provide both cooling humidification and are
sometimes the best solution in difficult climates
especially for offices and public buildings.
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Mechanical means
continued
Heaters
unnecessary in the Nigerian climate
may create additional comfort during the cold
harmattan period when combined with
humidification
 Small portable units are appropriate
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Need for Heating and
Cooling System
heating and cooling systems is determined by
comfort conditions
(humidity and temperature)
the duration of these conditions
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Need for Heating and
Cooling System
alternatives to heating and cooling systems
Clothing
flexible use of space
outdoor living and sleeping
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Need for Heating and
Cooling aids
System
Fans
criteria
high temperature and humidity
Evaporative coolers
Air Conditioners
Heaters
high temperature humidity (25%
temperature>35oc
or
temperature>30oc
and humidity>70%
day temperature <16oc
and diurnal range <10oc
or
day temperature <18oc
and diurnal range>10oc
Duration (months)
Never
requirement
not required
1
2
>3
desirable
highly desirable
desirable; need for cross ventilation
Never
not required
1
2
>3
Never
1
2
>3
Never
1
luxury
highly desirable
desirable
not required
luxury
desirable
highly desirable
luxury
desirable
2
>3
highly desirable
permanent heating required
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Factors Affecting Air flow
through Buildings
External Features and Factors that affect air flow
wind speed
 Barriers
direction
 Vegetation
dust content
 building shape and
orientation
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Factors Affecting Air Flow
through Buildings
 Building orientation should take maximum
advantage of wind direction.
 Barriers and vegetation may create wind
shadows and channel air flow.
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Factors Affecting Air flow
through Buildings
 Position of the building with respect to other
buildings should ensure adequate spacing to
avoid wind shadows and achieve air movement.
 Dusty winds should be avoided or filtered by
vegetation.
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Factors Affecting Air Flow
through Buildings
Number and Size of Openings
Effective cross ventilation requires at
least two openings - an inlet and an outlet
on opposite, or at least adjacent walls of an
enclosure.
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Factors affecting Air flow
through Buildings
 If a room has one opening, air movement within
the room remains negligible even for high
external winds speeds
 comfort conditions worsen at higher wind speeds due
to pressure build up.
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Factors affecting Air flow
through Buildings
Effect of window size and wind direction on average air velocities in
buildings
Wind Direction Outlet Size
Inlet size
1/3
2/3
3/3
1/3
36
34
32
2/3
39
37
36
Perpendicular
3/3
44
35
47
None
13
13
16
1/3
42
43
42
2/3
40
57
62
Oblique
3/3
44
59
65
None
12
15
23
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Factors Affecting Air flow
through Buildings
the average air velocity increases with
 increase in size of inlet and outlet
 increase in size of outlet with respect to
the inlet.
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Factors Affecting Air flow
through Buildings

for rooms without cross ventilation
the inlet size is the proportion of window
width to wall length
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Factors Affecting Air flow
through Buildings
Position of Openings
the position of outlets (on the leeward side) and
that of inlets (on the windward side) has a
marked effect on the pattern of air flow within
an enclosure.
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Factors Affecting Air flow
through Buildings
Effect of window location and wind direction on
average air velocities in buildings
Inlet Width
1/3
1/3
1/3
2/3
2/3
2/3
3/3
3/3
3/3
Outlet Width
1/3
2/3
3/3
1/3
2/3
3/3
1/3
2/3
3/3
Windows in
Windows in
opposite walls
adjacent walls
Wind Perpendicular
Wind Oblique
Wind Perpendicular
Wind Oblique
35
39
44
34
37
35
32
36
47
42
40
44
43
51
59
41
62
65
45
39
51
51
50
-
37
40
45
36
37
-
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Factors Affecting Air flow
through Buildings
 In plan, air velocity distribution is affected by
the relative position of inlet and outlet for a
given wind direction.
 The incoming air stream takes the shortest
course of least resistance to the outlet.
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Factors Affecting Air flow
through Buildings
Openings located diagonally
will cause air flow through the
centre of the room
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Factors Affecting Air flow
through Buildings
Larger portion of a room
remains unventilated if
openings are situated
directly opposite each
other on one side of
opposite walls or close
together on adjacent wall
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Factors Affecting Air flow
through Buildings
Low inlets tend to direct the air flow towards the
floor
 High inlets direct the air flow towards the
ceiling
 Centrally placed inlets produce air flow in the
general direction of the external wind.
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Factors Affecting Air flow
through Buildings
For multi-storey buildings,
with centrally placed inlets,
the wind flow is deflected
towards the floor on the
ground floor while it is
deflected towards the ceiling
on upper floors.
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Factors Affecting Air flow
through Buildings
Opening Components
 Canopies
 variously hung windows
 sashes
 curtains
 louvers and venetian blinds
mosquitoes screens
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Factors Affecting Air flow
through Buildings
Canopies
 directs air flow towards the ceiling
 air flow can be reversed towards the floor by
leaving a gap between the canopy the opening
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Factors Affecting Air flow
through Buildings
Louvres and venetian blinds
Directs air flow upwards or
downwards according to
their angle of inclination.
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Factors Affecting Air flow
through Buildings
Sashes deflects air flow
upwards but reversible
pivot sashes can deflect
it downwards.
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Factors Affecting Air flow
through Buildings
 Mosquito screens depending on material and
perforation reduce air flow by 30% to 70%
 Nylon screens reduces air by 35%
 This should be kept in mind when calculating
size openings for effective ventilation
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria
Factors Affecting Air flow
through Buildings
Top hung outward-opening
windows deflect air towards the
ceiling.
Side hung windows deflect air
towards the hinged side when
open outwards and vice-versa.
Roller shutters deflect wind
downwards when partially open.
ARC 810: Building Climatology
Department of Architecture, Federal University of Technology, Akure, Nigeria