1
UR B A N G E O M E T R Y A S A DE T E R M IN A NT O F
O U T DO O R T H E R M A L C O M F O R T
D . S . R A N A S I N G H E
J a n u a r y 2 0 0 4
2
D E C L A R A T I O N
I declare that this dissertat ion represents my own work,
except where due acknowledgement is made, and that it has not
been previously included in a thesis , dissertat ion or report
submitted to this university or to any other inst itut ion for a
degree, diploma or other qualif icat ion.
……………………………………….
Ranasinghe, D.S.
Acknowledgement
I take this opportunity to offer my sincere gratitude to all who helped me in
the preparation of this dissertation. Among them I am deeply thankful to,
3
Archt. Vidura Sri Nammuni, Head, Department of Architecture, Archt.
Prasanna Kulatilake, coordinator, M.Sc. dissertations and Dr. Indrika Rajapakase for
the comments and guidance at the early stages which
placed me on correct path…
Dr. Rohinton Emmanuel, Senior Lecturer, Department of Architecture, who was
the tower of strength throughout this study and encouraging me to take the
challenge of explore new “heights”…
Narein aiya who’s valuable comments and making me to think more and
more with necessary depth and breadth…
Mr. Chathura Masakorala, Technical Officer and Mr. Chandana
Amunuthuduwa, Computer Lab Assistant, who helped me to make my
research part a success…
Mr. Manoj Peiris of UDA and Athauda aiya for helping me to find out
necessary documents for my research work...
Officer in Charge and the Staff of the Pettah Police Station who allows me to carry
out
the research work without any disturbance…
My colleagues Ruwan, Nirodha, Nalika, Aish, Amali, Koththi, Samantha and all,
who helped me numerous ways…
Sewwandi, for numerous criticisms, arguments and comments which placed
me in different avenues on a broader view…
My two brothers, Tharaka & Mayuka who were there when ever I need support and
encouragement…
Last, but by no means, not least my dear parents who allowed me to start a career
on architecture six years ago regardless of the trend and
continuing that support and guidance throughout my university education…!
A B S T R A C T
Architecture through the time has been as
important factor that facilitate life styles and
environment. The challenge for architects is to create
4
psychologically and physically comfortable indoor and
outdoor spaces. The outdoor public spaces have
become the heart of the civic life of the city where
people carry out their activities that binds a community.
All the spatial scales in the built environment
obeys to rhythms and major forces, which enforce their
laws that must be learnt and respect (Bouillot, 2002).
The success of these spaces, especially urban public
spaces is depending on many factors, of which, the
level of thermal comfort is seen as an important aspect.
Although the equatorial life is partly outdoor
phenomenon, the modern urban design has failed to
facilitate such living in a climatically pleasant manner.
Recent studies worldwide have indicated that
the influence of densely built urban areas on the
formation of urban climatic conditions and particularly
on the determination of the microclimate. The
evaluation of influence of urban geometry on the
microclimate and the human comfort in urban spaces
in such areas are among the main aims of the research
project. It will also be useful to reveal misreferences,
state recommendations and supply tools and tracks for
the design.
Nowadays it is more than evident that improving
the quality of life in urban centres does not require only
successful buildings. It also requires climatically sensitive
urban public spaces which could enhance and enrich
the urban life.
URBAN GEOMETRY AS A DETERMINANT OF OUTDOOR THERMAL COMFORT
C O N T E N T S
Declaration i
5
Acknowledgements
ii
Table of Contents iii
List of Figures vi
List of Tables ix
INTRODUCTION 07
Observation
02
Justification 04
Intention of the study 05
Objectives 05
Hypotheses 05
Scope & Limitations
06
Method of Study 07
C h a p t e r O n e
1.0 ARCHITECTURE, THERMAL COMFORT & URBAN DESIGN
08
1.1 ARCHITECTURE: THE PURPOSE
08
1.2 THERMAL COMFORT 10
1.2.1 Thermal Comfort Indices 12
1.2.1.1 Predicted Mean Vote 12
1.2.1.2 Operative Temperature
13
1.2.1.3 Temperature Humidity Index 14
1.2.2 Indoor Thermal Comfort 15
1.2.3 Outdoor Thermal Comfort
15
1.3 URBAN SPACE 16
6
1.3.1 Definition 16
1.3.2 Elements of Urban Space
17
1.4 URBAN MORPHOLOGY
17
1.4.1 Building Morphology 18
1.4.2 Urban Density 19
1.4.3 Street Layout & Orientation 20
1.4.4 Height to Width Ratio 21
1.4.5 Vegetation 22
1.5 CONCLUDING REMARKS 23
C h a p t e r T w o
2.0 CLIMATE CONSIDERATIONS IN URBAN DESIGN 24
2.1 CLIMATE CHARACTERISTICS OF URBAN DESIGN 24
2.2 IMPACTS OF URBANIZATION ON CLIMATE 27
2.2.1 Urbanization
27
2.2.2 Urban Heat Islands
28
2.3 URBAN DESIGN STRATEGIES 30
2.3.1 Design Strategies for mitigation of UHI
31
2.3.2 Shadow Umbrella 31
C h a p t e r T h r e e
3.0 SHADOW UMBRELLA : RESEARCH DESIGN 34
3.1 RESEARCH DESIGN 34
3.1.1 Selection of Cases & Rationale 34
7
3.1.2 The Site 35
3.1.2.1 Context
35
3.1.2.2 Physical characteristics
36
3.1.3 Method of Study 38
3.1.3.1 Organization of the Study 38
3.1.3.2 Modifications 40
3.1.4 Analysis Techniques
42
3.1.5 Hypotheses 43
C h a p t e r f o u r
4.0 RESULTS AND ANALYSIS 44
4.1 BACKGROUND FOR RESEARCH 44
4.2 ON SITE DATA MEASUREMENT
45
4.3 EXISTING CASE 48
4.3.1 Shading Patterns 49
4.3.2 Thermal comfort levels 51
4.4 CASE ONE 58
4.4.1 Shading Patterns 59
4.4.2 Thermal comfort levels 63
4.5 CASE TWO 78
4.5.1 Shading patterns 79
4.5.2 Thermal Comfort Levels 81
CONCLUSIONS 89
Design implications
90
Limitations 96
8
Directions for further study
97
BIBLIOGRAPHY 98
APPENDICES 101
L I S T O F F I G U R E S
1. The Mongolian Yurt 01
2. Sri Lankan village house 01
3. Predicted Percentage of Dissatisfied (PPD) as a function of …
12
4. Relationship of PMV and Operative Temperature
14
5. Urban Morphology
18
6. Urban Street Layout
20
9
7. Streets shaded by the built masses 22
8. Köppen Climate Classification System 24
9. Urban Heat Island 28
10. Sun path diagram for 80 South latitude
32
11. Eastern and Western extremities
33
12. Colonial Buildings 35
13. Dutch Museum 35
14. Pettah
37
15. Unplanned developments causing disorderly urban environments 38
16. Hobo 45
17. Existing Street (Modelled in DEROB) 45
18. Actual Temperature vs. Simulated Temperature 47
19. Existing Streets
48
20. Shading Pattern for E/W & N/S Running Streets 49
21. Shaded North - South Street (At 3.00 p.m.) 50
22. East-West Street 51
23. North - South Street 51
24. Comparison of temperatures in two streets 51
25. Shadow Patterns, thermal comfort level and operative
temperature of E/W Street at 10.00 a.m.
52
26. Shadow Patterns, thermal comfort level and
operative temperature of E/W Street at 12.00 noon
53
10
27. Shadow Patterns, thermal comfort level and
operative temperature of E/W Street at 3.00p.m. 54
28. Shadow Patterns, thermal comfort level and operative
temperature of N/S Street at 10.00 a.m.
55
29. Shadow Patterns, thermal comfort level and operative
temperature of N/S Street at 12.00 noon 56
30. Shadow Patterns, thermal comfort level operative
temperature of N/S Street at 3.00p.m.
57
31. Modified Streets & H/W ratios 58
32. Shading Pattern for East/ West Running Streets
59
33. Shading Pattern for North/ South Running Streets 60
34. Shading Pattern for Northeast/ Southwest Running Street
62
35. Shading Pattern for Northwest/ Southeast Running Street
63
36. Modified building heights of the streets
63
37. Comparison of temperatures in relation to the building height
- East/ West Street 64
38. Comparison of temperatures in relation to the building height
- North/ South Street
64
39. Comparison of temperatures in relation to the building height
- Northeast/ Southwest Street 65
40. Comparison of temperatures in relation to the building height
- Southeast / Northwest Street 65
41. Shadow Patterns and operative temperature of
N/S Street at 10.00 a.m. 66
11
42. Shadow Patterns and operative temperature of
N/S Street at 12.00 noon
66
43. Shadow Patterns and operative temperature of
N/S Street at 3.00 p.m. 67
44. Shadow Patterns and operative temperature of
N/S Street at 3.00 p.m. 68
45. Shadow Patterns and operative temperature of
N/S Street at 12.00 noon 68
46. Shadow Patterns and operative temperature of
N/S Street at 3.00 p.m. 69
47. Shadow Patterns and operative temperature of
NE/SW Street at 10.00 a.m.
70
48. Shadow Patterns and operative temperature of
NE/SW Street at 12.00 noon 70
49. Shadow Patterns and operative temperature of
NE/SW Street at 10.00 a.m.
72
50. Shadow Patterns and operative temperature of
NE/SW Street at 12.00 noon 72
51. Shadow Patterns and operative temperature of
NE/SW Street at 3.00 p.m.
73
52. Shadow Patterns and operative temperature of
NW/SE Street at 10.00 a.m. 74
53. Shadow Patterns and operative temperature of
NW/SE Street at 12.00 noon 74
54. Shadow Patterns and operative temperature of
NW/SE Street at 3.00 p.m.
75
12
55. Shadow Patterns and operative temperature of
NW/SE Street at 10.00 a.m.
75
56. Shadow Patterns and operative temperature of
NW/SE Street at 12.00 noon 76
57. Shadow Patterns and operative temperature of
NW/SE Street at 3.00 p.m.
76
58. Modified Streets & H/W ratios – Case 2
78
59. Shading Pattern for North/ South Running Streets 79
60. Shading Pattern for Northeast/ Southwest Running Street
80
61. Shading Pattern for Northwest/ Southeast Running Street
80
62. Modified building heights of the streets
81
63. Comparison of temperatures in the North/ South Streets 82
64. Comparison of temperatures in the Northeast/ Southwest Streets
82
65. Comparison of temperatures in the Northwest/ Southeast Streets
83
66. Shadow Patterns and operative temperature of
N/S Street at 10.00 a.m. 84
67. Shadow Patterns and operative temperature of
N/S Street at 12.00 noon 84
68. Shadow Patterns and operative temperature of
N/S Street at 3.00 p.m. 85
69. Shadow Patterns and operative temperature of
NE/SW Street at 10.00 a.m.
85
13
70. Shadow Patterns and operative temperature of
NE/SW Street at 12.00 noon 86
71. Shadow Patterns and operative temperature of
NE/SW Street at 3.00 p.m.
86
72. Shadow Patterns and operative temperature of
NE/SW Street at 3.00 p.m.
87
73. Shadow Patterns and operative temperature of
NE/SW Street at 3.00 p.m.
87
74. Shadow Patterns and operative temperature of
NE/SW Street at 3.00 p.m.
88
L I S T O F T A B L E S
Table 1 – Materials used in DEROB
44
Table 2 – Actual and Simulated Data, Pettah.
46
14
I N T R O D U C T I O N
15
INTRODUCTION
Architecture is the symbol of a civilization. “…without an
architecture of our own, we have no soul of our own civilization” -
Frank Lloyd Wright
Dwellings or houses have been one of an essential need of man
since the early civilizations. During that pre-historic stage, the most
essential architectural space (Relph, 1976) for them is their houses.
As Moore (1993) states, the primary housing unit is the shelter. The
main purpose of the shelter during that time is to reduce the range of
local climatic variations. Therefore, the ‘house form’ was varied with
the climatic conditions. The Sri Lankan village house, Eskimo Igloo,
North American Indian Tipi, Mongolian Yurt, Matmata dwellings in
Sahara, dome hut of Banbuti Pygmies etc. (Moore, 1993) are fine
examples for the climate responsive house forms.
Fig. 1- The Mongolian Yurt Fig. 2 - Sri Lankan village house
Rapoport (1969) states that, in architecture, climate is only a
modifying factor and the determinant factor should be the culture.
16
“The responses vary from place to place because of changes and
differences in the interplay of social, cultural, ritual, economic and
physical factors. Also with the passage of time” (Rapoport, 1969: 46)
However, anywhere in the world, the vernacular architecture
was emerged as a response to the climatic conditions in its form and
the use of materials. Cultural matters were considered as secondary
generators. The cultural and other psychological matters dominated
architecture after the man started to control the nature.
“Instead of building walls of local bamboo, which is
closely spaced to keep out rain while admitting light and
air, the white man put up solid walls to keep out light and
air and then cut windows in the walls to admit the light
and air. Next, he put glass panes in the windows to admit
light but keep out the air. Then, he covered the panes with
blinds and curtains to keep out the light too”
(Moore, 1993: 39)
This statement illustrates how the western thinkers have adopted
various mechanical means neglecting the passive design methods.
Those were the results of the centuries of trial-and-error experiments by
the tribes. Those mechanical systems have made us consume more
energy as well as many environmental hazards.
The reason for the extensive use of energy is to make the space
comfortable physically. People are always in demand for comfort.
Thus main purpose of architecture is also to make people comfort
physically as well as psychologically. The thermal comfort level of a
space facilitates better physical or bodily experience. Thus, it facilitates
the expected spatial quality. These are valid for any architectural
space (Relph, 1976) regardless of its location - indoor or outdoor.
17
O B S E R V A T I O N
Contemporary designers are more concerned on the
psychological comfort of the space or the beautification of the space.
Especially for a tropical country like Sri Lanka, that “beautification” is
inadequate to provide a better spatial experience. Therefore, it is a
challenge for the architect to create functional, comfortable, lightly
ventilated and pleasant interior and exterior spaces creating beautiful
objects and places.
Recent studies worldwide have indicated the great influence of
densely built urban areas on the formation of urban climatic conditions
and particularly on the determination of the microclimate. This has
always been true to the Sri Lankan context as well. Some urban areas
in Sri Lanka, especially Colombo Metropolitan area, this phenomenon
could be observed clearly.
Due to the thermal discomfort in these urban outdoors people
decline to use these urban spaces. Lots of public spaces have become
“dead spaces” during the daytime; merely because of they are not
habitable. These spaces create “voids” in the middle of urban settings
deteriorating the urbanity of the city. It also affects Neighborhood
livability, street life, social interactions between neighbors and level of
outdoor activities etc. (Hafiz, 2002)
The transformation in “urban physical environment” has made a
physical discomfort in the area. This chaotic urban situation is a result of
unskilled handling of buildings and open spaces. These haphazard
developments have caused many negative effects such as blocking
wind flow patterns, retaining heat etc. As a result, the cities have
become warmer places than the surrounding rural areas, creating an
Urban Heat Island. This has affected the urban microclimate and the
urban quality of life as well. In addition, the mechanical systems should
18
be utilized to achieve thermal comfort consuming more and more
energy.
This is a very crucial subject area, which should be taken in to
consideration seriously because in the future, it may be a danger to the
humankind as well. The design professionals such as architects and
urban designers should intervene in these situations to make cities a
healthy place to breathe.
J U S T I F I C A T I O N
“Architecture is a physical, emotional and
intellectual experience. It facilitates man’s bodily comfort,
emotionally attaches him in to it, and, as a work of art,
through symbolic communication leads to him towards a
higher realm of contemplation”
(Kulatilake, 1994: ii)
It states that the architecture should be experienced in all senses
covering both physical and psychological experience. Human mind
experiences it psychologically and human body haves it physically. In
physical experience, the warmth or the temperature of a space
contributes more to the spatial experience. That is called the ‘Thermal
Comfort’ of a space. An architectural space (Relph, 1976), which has a
good thermal comfort level, facilitates desired spatial experiences.
“All architecture is shelter, all great architecture is the design of space
that contains, cuddles, exalts or stimulates the persons in that space”
(Johnson, 1990). According to above words the architecture of a particular
space – interior or exterior - should “contain, cuddle, exalt and stimulate” the
people in that space. That should be the purpose and the ultimate goal of
architecture. Therefore, the architectural space (Relph, 1976) should be a
pleasant place, physically and psychologically to accomplish that goal.
19
The recent trend in the Sri Lankan urban context as cited in the
previous chapter is towards a haphazard development. This has
caused many chaotic situations, especially in the urban microclimate.
High air temperature, excessive relative humidity, zero or low wind
speed etc. has deteriorated the urban microclimate.
As Basnayake (2002) explains, a healthy urban environment is
vital for genuine urban renaissance and at the same time, it caters as a
healing space for the majority of urban dwellers. However, the
“physical discomfort” is a barrier for the people to experience and
make use of the urban space. It may affect the people negatively,
since it avoids interaction with other people, which is essential for
human habitation. Converting those spaces to thermally comfortable
will fulfil the primary need for usage.
Therefore, it is now the time for design professionals to interfere
without hesitation and correct these trends to rejuvenate our outdoor
spaces and make a healthy urban physical environment
INTENTION OF THE STUDY
Intention of this study is to examine the role of urban geometry or
urban morphology in the provision of thermally comfortable outdoor
spaces. In doing so, it will develop urban shading patterns that
facilitate climate conscious urban design in the equatorial tropics, with
special reference to Sri Lankan urban contexts.
OBJECTIVES
Find out ways to utilize the urban geometry as a shading
device or Shadow Umbrella to enhance the urban thermal
comfort.
Discuss the impact of shading on the outdoor thermal
comfort.
20
H Y P O T H E S E S
Shading or shaded spaces have a positive effect on the
thermal comfort level of the people using those urban
spaces.
The manipulation of urban masses and increased height to
width ratio of the built mess increases the level of thermal
comfort.
The orientation and the ratio of building height to the width of
the streets considered can be consciously modified in order
to achieve thermally comfortable urban space.
S C O P E & L I M I T A T I O N S
Architecture is for people. Therefore, architect should provide the
people with sufficient physical and psychological comfort. Thermal
comfort contributes for physical comfort mostly. Therefore, the thermal
comfort is essential in indoors as well as outdoors.
This study is mainly focussed on urban outdoor spaces. In a
tropical country like Sri Lanka, outdoor spaces are used extensively. In
addition, it is more important, because it is not feasible to regulate
outdoor climate mechanically.
In the equatorial tropics the best approach to thermal comfort is
reducing radiant heating of the environment. This can be achieved by
various strategies. However, shading is the primary and most effective
strategy (Emmanuel, 1993b; Givoni, 1998). Other strategies should be
implemented in the light of shading.
21
The primary tool to achieve shading is urban masses. The study
will explore the relationship between urban geometry and the outdoor
thermal comfort. That means the building morphology (mass, height,
orientation etc.), urban density, street lay out, height to width ratio etc.
or in other words urban geometry.
In addition, computer software will be used to simulate the
shading patterns and thermal comforts in various urban geometries.
The thermal comfort will be simulated using “DEROB-LTH” software,
which is designed for indoor use. Therefore, the dummy materials
should be used for sky and the roads. In addition, ventilation is
disregarded.
Urban space consists of streets, squares & blocks. Since the study
is on human thermal comfort, it is more appropriate to consider spaces
mostly used by people. Therefore, the shading of pedestrian paths are
considered.
Though Sri Lanka does not have much variation in climate
(Emmanuel, 1993b; Koenigsberger, 1974), it has very slight variations
during some periods. The study is carried out for the hottest period of
the year, i.e. April and May. And the thermal comfort levels are
simulated for emphasize the hottest times of the day.
M E T H O D O F S T U D Y
The study will be a research-based simulation study. The
objective is to evaluate the effects of the “building geometry” on the
outdoor thermal comfort by manipulating urban form. Therefore, after
setting the theoretical background and hypothesis for the study,
research work is carried for a selected urban setting.
A field survey will be carried out in the selected area to measure
the actual temperature data. Those data will be compared with the
simulated data to develop an equation in order to calibrate the
simulated data in the future.
22
The main parameters for urban forms are its height to width ratio
and the orientation of the building. The shading patterns for the
modified urban settings are calculated on computer using AutoCAD
with 3 D models. Since this is a simulation study, the required period of
the year and time is achievable. The modelled urban masses are
simulated to obtain the shading patterns in relation to their geometry.
After that those modified urban settings are simulated further to
evaluate their thermal comfort levels. That work is also carried out on
computer using parametric building energy simulation programme
called DEROB – LTH, which is capable of analysing simulated
environments thermally. The temperature levels will calibrate using the
previously developed equation.
Finally, urban design implications and conclusions are drawn
upon the comparisons of comfort levels for changes in shading
patterns and built masses in accordance with the derived hypotheses.
23
C H A P T E R O N E
A R C H I T E C T U R E , T H E R M A L C O M F O R T &
U R B A N D E S I G N
24
C H A P T E R O N E
1.0 ARCHITECTURE, THERMAL COMFORT & URBAN DESIGN
Architecture has bonded with the human kind since the origin of
man. It served man for a better life. For the pre-historic man, the
climate was an “uncontrollable force”, to their life. They did not have
any other option other then to adopt it. One of the tools they used to
counteract this phenomenon is architecture. As a result various built
forms were emerged around the world. Even today people explore the
possibilities to counteract this uncontrollable force.
This chapter will discuss the importance of thermal comfort in
architecture to man. It will also further examine the reasons for the
present deterioration of urban microclimates at city scale. The usage of
built forms to react these situations will also be discussed.
1.1 ARCHITECTURE: THE PURPOSE
Architecture is for people and it should facilitate the life on earth.
It should serve the mankind. “Man is in the foundation of every
culture and architecture serves man” (Anthonides, 1992: 161)
The primary space – the shelter – is the basic element, which architects
play around to create architecture. Shelter defines a space, which could be
enhanced by architecture. It should be more than a functional building and
a visual satisfaction.
Sri Nammuni (1987) states the shelters whose impact on the user
is profound and enduring and one that “distracts” him from the specific
(building) to the contemplation of the abstract (Thus away from his
physical constraints, anger, frustration, poverty etc.) could be art and
therefore architecture.
25
The experience of a space is depended on what the user
expects from that particular space. In other words user needs or
aspirations. The architect’s role is to realise the aspirations of the user
and create a building that responds positively to those needs (Sri
Nammuni, 1987).
“The task of the designer is to create the best possible indoor
climate. The occupants of the building judges the quality of the design
from a physical as well as emotional point of view” (Koenigsberger.
1974:41)
The user needs may be divided in to qualitative and quantitative
ones. Sri Nammuni (1987) states that, when the qualitative needs are
addressed the building is transformed in to architecture. However, the
basic human needs can be divided in to primary or physical needs and
secondary or psychological needs. Physical needs include air, food,
water, sleep, shelter and temperature. Psychological needs include
such tangibles like sense of belonging, personal affection, self-esteem
etc. (Dayaratne, 1987)
These physical needs are essential for the protection and
preservation of life on earth. “None of the psychological needs are of
such critical nature that an individual would curl up and die in four
days if deprived of it” (Dayaratne, 1987:46).
Dayaratne (1987) quoting Maslow formulates four basic levels of needs
for a healthy life.
1. Physical Needs – hunger, thirst.
2. Safety Needs – security, order, freedom from pain, discomfort
and threat.
3. Belongingness and Love Needs – love, sex, affection,
friendship, identification.
4. Esteem Needs – man’s desire for self fulfilment.
26
Dayaratne (1987) also quotes the Danish psychologist Ingrid Ghel
stating that there are three basic types of needs which satisfies a good
living environment.
1. Physiological Needs – sleep. Rest, food, hygiene, sex, light, air,
sun.
2. Safety Needs – general house safety, safety precautions,
avoidance of pollution, noise etc.
3. Psychological Needs – privacy experience, contact, activity,
play structuring.
In the above two instances the physical needs were rated as a
“higher need”, but not as the “sole need”. It should be assisted by
other psychological needs. However, Maslow and Ghel have given a
higher place for temperature. It reveals that the temperature level of a
space is one of the primary needs for the physical comfort as well as
the well being of man. That should also apply to macro scale, which
means urban space as well.
The provision of a mere hygienic building is bad. But, providing
an unhygienic building is “worse”.
1.2 THERMAL COMFORT
Every second, the Earth receives from the Sun, such a large
quantity of energy that in twenty minutes it would provide the
necessary energy for mankind for a year. This fact shows the amount of
heat received by earth everyday (Castanheira, 2002). This excessive
amount of heat is the main cause to increase the temperature on
earth.
As cited above, thermal comfort is essential for the man to lead
a healthy life. Therefore, since the early periods, man has tried to
create thermally comfortable environments. The vernacular house
27
forms like Sri Lankan village house, Eskimo igloo, North American Indian
Tipi, Mongolian Yurt, Matmata dwellings in Sahara, dome hut of Banbuti
Pygmies etc. (Moore, 1993) are good examples for such attempts.
Thermal comfort is highly subjective sensation. “Criteria of total
comfort depend up on each of the human sense” (Koenigsberger,
1974:41). However, it is defined in the ISO 7730(1994) as “The condition
of mind that which expresses satisfaction with the thermal
environment”. Cheung (2003) states that, the thermal comfort occurs
when there is a thermal equilibrium in the absence of regulatory
sweating between the heat exchange between the human body and
the environment.
Thermal comfort is an indicator, which cannot be easily
converted in to physical parameters. However, thermal comfort can
be defined more qualitatively as the range of climatic conditions which
most of the people feel comfortable, neither cold nor warm. In other
words, neither shivering nor sweating.
Fanger (1970) states that two conditions must be fulfilled to
maintain thermal comfort. First is the actual combination of skin
temperature and the body’s core temperature which provides a
sensation of thermal neutrality. Second is the fulfilment of the body’s
energy balance; the heat produced by the metabolism should be
equal to the heat lost from the body. Thermally neutral sensations are
outlined by the temperature, skin temperature and activity level.
The control of energy balance in the human body is described in
the following equation (Cheung, 2003).
E + Q + S = M – W Where, S = Rate of heat storage of human body, W/m2
M = Metabolic rate of human body, W/m2
W = Mechanical work produced by human body, W/m2
E = Rate of total evaporative loss due to evaporation of sweat, W/m2
Q = Total rate of heat loss from skin (dry heat exchange), W/m2
28
Fanger (1970) has derived a comfort equation out of the above
equation for the heat balance. It is a function of six parameters which
influences the thermal comfort.
f (M , I cl , v , tr, ta , Pw ) = 0 where, M = Metabolic Rate (met)
Icl = Cloth Index / Clothing Level (clo)
v = Air Velocity (m/s)
tr = Mean Radiant Temperature (oC)
ta = Ambient Air Temperature (oC)
Pw = Vapour Pressure of Water in Ambient Air (RH)
This equation describes the relationship between the measurable
physical parameters and thermally neutral sensation as experienced by
an average person.
1.2.1 THERMAL COMFORT INDICES
Interest to establish a thermal comfort criterion dates back about
150 years. Most of them were on industrial buildings and sites such as
coal mines, textile mills etc. During that period the accidents and
illnesses were very common. (Koenigsberger, 1974)
During the past few decades attempts were made by various
people to derive thermal comfort scales. The very first estimates come
together in the effect of air temperature, air velocity and relative
humidity. Later on physiological responses like radiant temperature,
metabolic rates and clothing levels were also taken in to consideration.
29
Fig. 3 - Predicted Percentage of Dissatisfied (PPD) as a function of Predicted Mean Vote (PMV)
Among the more recent sensible indices, the Predicted Mean
Vote (PMV) (Fanger, 1970) Operative Temperature (OT) and
Temperature Humidity Index (THI) are most widely known due to their
association with the modem indoor climatic standards. (ISO 7730, 1994)
1.2.1.1 PREDICTED MEAN VOTE (PMV SCALE)
Danish scientist P.O. Fanger (1970) has developed the
Predicted Mean Vote (PMV Scale), which is a seven point thermal
sensation scale ranging from -3 (cold) from +3 (hot). Zero –“ 0 ” -
represents the neutral sensation.
PMV establishes a thermal strain based on steady-state heat
transfer between the body and the environment and assigns a comfort
vote to that amount of strain. PPD is the Predicted Percentage of
Dissatisfied people at each PMV. As PMV changes away from zero in
either the positive or negative direction, PPD increases. A curve has
been developed to predict the percentage of dissatisfied as a function
of Predicted Mean Vote.
P redi cted Mean Vote
Pre
dic
ted
Pe
rce
nta
ge
of
Dis
sati
sfie
d
30
PM
V
1.2.1.2 OPERATIVE TEMPERATURE (OT)
The ISO 7730 defines Operative Temperature as uniform
temperature of a radiantly black enclosure in which on occupant
would exchange the same amount of heat by radiation plus
convection as in the actual non-uniform environment.
The combined effects of air and mean radiant temperature
combined into a single index, the operative temperature. The
Operative temperature is defined as the uniform temperature of an
imaginary enclosure which man will exchange the same dry heat by
radiation and convection as in the actual environment.
Fig. 4 – Relationship of PMV and Operative Temperature Source: IS0 7730; 1994
1.2.1.3 TEMPERATURE HUMIDITY INDEX (THI VALUE)
Operat i ve Temperature
31
THI value is another index used to evaluate thermal comfort level
of a space. Unlike other two indices THI value is relatively easier to use.
It requires only the Relative Humidity and Dry bulb Temperature.
The final figure for the THI value will predict the thermal comfort
level of the space.
THI 21 – Most of the people deemed comfortable
24 – 50% of the people deemed comfortable
26 – Uncomfortable
1.2.2 INDOOR THERMAL COMFORT
“The task of the designer is to create the best possible indoor
climate” (Koenigsberger, 1974: 41). The indoor spaces are feasible to
regulate. Because, indoor spaces are comparatively enclosed spaces.
The volume and the shape of the space are fixed. Effects of the outside
natural forces can be controlled or mitigated. Because of the
predetermined volume of the space there is a possibility of using
mechanical means to control the meso-climate.
However, the use of passive design methods (non-energy use) is
more appropriate in every aspect. It is less harm to environment as well
as energy saving. There are various passive design strategies to control
the indoor thermal comfort of a space. Use of thermal resistant
materials, position of openings, shading devices are few of them.
THI = 0.8 x DBT + (RH x DBT) 500
Where, DBT – Dry Bulb Temperature (0F)
RH – Relative Humidity (%)
32
The indoor thermal sensation is affected positively as well
as negatively by the outside microclimate. Therefore, it is important to
think about the outside situation when considering indoor climates.
1.2.3 OUTDOOR THERMAL COMFORT
In the equatorial tropics outdoor spaces are well in use as the
indoor spaces. That was because the absence of the freezing cold as
the temperate regions and unbearable heat in indoors.
Outdoor space includes cities or urban spaces. These are not
enclosed as indoor spaces and also not totally controllable. Therefore,
designers are thinking of mitigating the effects of climate rather than
controlling it. The comfort parameters are same as the indoor spaces,
but the comfort levels are different. Therefore, what is expected from
the mitigating strategies should be different. “Thermal comfort design
goals therefore have to be different for the outdoors and indoors”
(Emmanuel, 1993: 174).
Emmanuel (1993) states that, in the outdoors the heat balance is
maintained by the environment. In the equatorial tropics it is not
adequate to achieve thermal comfort. Comfort could be achieved by
combinations of various environment variables. Therefore, various
strategies are used to mitigate the effect of the climate on people.
In equatorial tropics, shading is the primary strategy to
accomplish this goal (Emmanuel, 1993; Givoni, 1998). However, the
other design strategies also need to support shading to achieve a
complete thermal comfort.
1.3 URBAN SPACE
33
1.3.1 DEFINITION
Character of a city or a built environment is described in relation
to its built form and level of activities. Thus an urban space could be
described as dense in form and intense in activities. (Prematilleke,
2000)
Madanipour (1996) quoting Zevi states that every building
functions in the creation of two kinds of space: it is internal space,
completely defined by the building itself, and its external or urban
space, defined by that building and buildings around it. Does this
means that space between every two buildings can be called as an
urban space? In addition, Bouillot (2002) says, “...the existence of the
urban space is conditioned by the existence of several buildings which
could dialogue together, if there is only one building in a place, there is
no urban space …”. That proves that the spatial quality of an urban
space could be enhanced by the presence of quality buildings.
Madanipour (1996) also states that architects are more
concerned on the physical fabric of the city and its aesthetic and
functional dimensional. Rob Krier (1979) says that, to clarify the
concept of urban space, it should include aesthetic criteria.
Therefore, an urban space should be a place with of built forms
as well as activities. However, to be a healthy and live urban space,
there should be a concern on aesthetic aspect as well.
1.3.2 ELEMENTS OF URBAN SPACE
As mentioned above, the physical fabric of an urban space is
one major concern of architects. Thus, the morphological elements of
34
urban space can be identified as parts of the physical fabric. L. Krier
(1979) states that a city and its public spaces can only be built in the
form of streets, squares and blocks of familiar dimensions and
character, based on the local tradition.
All those elements should be integrated appropriately to create
better urban spaces. The block consists of buildings and the streets and
squares are defined by blocks. Character of each of these elements
manipulates the perception of the urban space. Width of the street,
height and the size of the blocks etc. are few factors that contributed
to urban space.
1.4 URBAN MORPHOLOGY
Shading can be achieved by various means such as vegetation,
built masses etc. But, in the urban areas the most suitable way to
achieve shading is manipulation of urban masses (Emmanuel, 1993).
Manipulation of urban masses will create a complete shadow canopy
and thus a healthy urban environment.
The study of urban masses in urban geography can be called as
Urban Morphology (Madanipour, 1996). The oxford dictionary defines
morphology as “The science of form”. However, urban morphology
can be defined as the systematic study of the form, shape, plan,
structure and functions of the built fabric of towns and cities.
(Madanipour, 1996)
A city is formed mainly from the built and unbuilt forms. In other
words city or urban space can be identified as an organism consists of
streets, squares (R. Krier, 1979) and blocks (L. Krier, 1979). Therefore, in a
study on the urban morphology, these elements should be
emphasized. In addition to these physical elements, public activities
are also very important in an urban environment.
35
In an urban context, the building density increases substantially.
Recent studies worldwide have indicated the great influence of
densely built urban areas on the formation of urban climatic conditions
and particularly on the determination of the microclimate. The vertical
scale of the man made environment and the extent of the horizontal
area of the city often creates its own microclimate, which significantly
deviating from the macroclimate. Therefore, it is justifiable to discuss an
“Urban Climate” in an urban context.
Research in the recent past has pointed out some important
relationships between urban factors and the climate. Thus, the
hierarchies of such factors are important in urban climate
modifications. Oke (1977), points out that urban climate system is
composed of two distinct layers; the Urban Canopy Layer (UCL) and
the Urban Boundary Layer (UBL).
UBL is the overall atmospheric system that extends for many miles
above the cities. The characteristics of UBL are partially determined by
the city below. UCL on the other hand is that layer of atmosphere
where most of life occurs, from ground to the mean height of roofs.
Understandably climatic effects of urbanization is strongly felt in UCL.
1.4.1 BUILDING MORPHOLOGY
Fig. 5 - Urban Morphology Source: Kostoff, 1996:54
36
Building morphology means the study of the form of the
buildings. It includes form, shape, plan, size, orientation etc. The built
masses contribute to a large extent of the urban microclimatic
modifications than the urban surfaces. (Emmanuel, 1993)
The built patterns which are results of various building
morphologies provides positive as well as negative impacts of climate
on the urban life. it depends on how the urban designers and
architects handle the built forms. It facilitates design strategies such as
shading, cooling patterns and wind movement. On the other hand,
those built forms may retain heat masses, block wind patterns etc.
Shading is the primary tool for achieving the thermal comfort in
outdoors (Emmanuel, 1993). The profile of buildings is a major factor in
achieving shading. The shading patterns depend on the height, shape,
spacing and orientation of each and every building in an urban
setting.
1.4.2 URBAN DENSITY
The density of a built up area of a city affects the local climate of
and the thermal comfort of the inhabitants. Urban Density is the
distribution of urban elements on the ground such as houses, urban
alignments, empty plots, vegetation, water bodies etc. (Ait-Ameur,
2002). In addition, the spacing between buildings (including street
width) and average height of buildings also contributes to the urban
density.
High urban density causes the retaining of thermal masses,
blocking wind patterns etc. there should be a balance between built
an unbuilt spaces in a cityscape. A good climate conscious urban
design will manipulate the built masses to reduce the radiant heating
at the ground level. (Emmanuel, 1993)
37
Higher-buildings density often results in fewer trees and other
kinds of vegetation. Plants have a lower rate of healing during the
daytime and higher rate of cooling at night as compared with building
materials and other urban hard surfaces.
1.4.3 STREET LAYOUT & ORIENTATION
Street is an important element in an urban space. R. Krier (1979)
states that it provides a framework for the distribution of land and gives
access to the individual plots and it has more pronouncedly functional
character to fulfil human needs.
A road, in the presence of activities become a “street”.
Therefore, the nature of activities also contributes to the urban micro
climate. Besides, the well planned streets assists wind flow patterns.
Emmanuel (1993a) quoting Nieuwalt states that, to make the most of
wind movement should be higher than 1 m/s. If not, even the small
obstacles will alter the wind flow.
The orientation of streets affects the urban climate in several
ways:
Wind conditions in the urban area as a whole
Sun and shade in the streets and the sidewalks
Solar exposure of buildings along the street
Ventilation potential of the buildings along the street
38
The orientation of the street determines the annual and diurnal
patterns of solar radiation of the buildings along them and the spaces
between them, thus affecting the solar exposure of the buildings and
the comfort of the persons walking on the street. Orientation of urban
streets often determines the orientation of the buildings along the
streets, which in turn affect their solar exposure and daylight conditions.
In a hot-humid climate the main objectives related to The streets
layout are to provide maximum shade for pedestrians and minimum
solar exposure of the buildings along the streets.
Narrow streets provide better shading by buildings for pedestrians
on sidewalks than wide streets. However, shade for sidewalks can be
provided even in wide streets by special details of the buildings or by
trees.
A north-south orientation of a street may result in an east-west
orientation of buildings along and parallel to the street, which will
cause unfavourable solar exposure for these buildings. From the solar
exposure viewpoint an east-west street orientation is favourable
(Givoni, 1998)
1.4.4 HEIGHT TO WIDTH RATIO
The impact of the impinging solar radiation on the climate near
the ground depends on some extents to the height (H) of the buildings
Fig. 6 - Urban Street Layout Source: Kostoff, 1996:54
39
to the space (width) between them, namely the H/W ratio of the
spaces between the buildings.
Ludwig (1970) presents an analysis of the effect of the ratio on
the radiation and air temperature near the ground. His analysis shows a
the flat area, most of the impinging solar radiation is reflected away or
emitted, after absorption, as long wave radiation to the sky. In a
medium-density area (H/W ratio of 1l), much of the reflected radiation
strikes other buildings or the ground and is eventually absorbed at or
near the ground level. In the high-density area, most of the absorption
takes place high above the ground level. Consequently, the amount of
radiation reaching the ground, heating the air near the ground, is
smaller than in the case of the medium density.
In addition to this the width of the street and the geometry of the
abutting buildings manipulate the shading of the street. Therefore,
height of the edge buildings should be arranged in such a way to have
complete shading of streets during crucial times of the day. In
addition, the whole street layout with the correct height to width ratio
will facilitate good wind movement.
The streets are generally seen as areas for public circulation and
recreation. (L. Krier, 1979) Therefore, streets should be thermally
comfortable for the use of people. In addition, the height to width ratio
has a psychological effect on the users as well. It facilitates the feeling
of enclosure in a street. According to Bentley (et al. 1985), the ratio
should be higher than the 1: 3 to feel the enclosure of the street.
40
1.4.5 VEGETATION
“The purpose of natural elements is not so much to develop
negative aspects of tropical climate but to enhance the cooling
potentials of shading. …role of vegetation needs careful attention. It is
not just in providing shade that trees are important assets to climatic
urban design”. (Emmanuel, 1993)
Vegetation means the presence of trees in urban outdoors. Trees
have a good cooling potential if it is used correctly. It reduces the heat
radiation from large open areas where built mass is lower height.
The arbitrary use of trees may disturb the air movement of the setting.
Therefore, vegetation needs to be studied properly for their shading potential
and the ecological functions.
1.5 CONCLUDING REMARKS
Fig. 7 – Streets shaded by the built masses
41
This chapter has attempted to identify the importance of
thermal comfort to human life and architecture and it’s relationships at
city scale.
For a healthy life man should be in comfort both physically and
psychologically. Temperature level of a space is very important since it
is one of the primary factors for human existence. Man has tried and
still trying, to avoid the effects of climate since pre-historic times by
various means.
In the equatorial tropics, the life is part indoor and part outdoor.
Therefore, thermal comfort in outdoor spaces are also equally
important. Especially in the urban outdoors spaces. In urban setting,
shading is the best possible method to achieve thermal comfort. The
built masses are the most suitable to achieve shading in as urban
environment.
Ultimately, these urban spaces should be livable spaces.
Therefore, in addition to all these characteristics, those should be
thermally comfortable places. This should be the final goal of each and
every urban design strategy.
42
C H A P T E R T W O
C L I M A T E C O N S I D E R A T I O N S I N
U R B A N D E S I G N
43
C H A P T E R T W O
2.0 CLIMATE CONSIDERATIONS IN URBAN DESIGN
Climate has influenced the human dwellings since the origin of
man. Their house forms were direct responses to the regional climate.
The sole purpose of that reaction is a thermally comfortable space. The
development of cities has widened the consciousness of man on
public open spaces rather than private and indoor spaces. Later on,
the disorganized urbanization has caused various problems in the
cities’ microclimates. As a result, people started to find out various
urban design strategies to achieve comfortable spaces.
This chapter will discuss the climatic variations in the world and
how those were affected by the urbanization. In addition, it will observe
the urban design strategies used to mitigate the repercussions of
deteriorated microclimate.
2.1 CLIMATIC CHARACTERISTICS OF HOT-HUMID REGIONS
44
Fig. 8 - Köppen Climate Classification System Source: www.blueplanetbiomes.org/climate_map.htm
Since pre-historic period, climate has controlled almost every
aspect of human life. Their houses, clothing, food etc. shows the direct
influence of climatic factors. Climate is “…an integration in time of the
physical states of the atmospheric environment, characteristic of a
certain geographical location. (Koenigsberger, 1973; 3)
The tropical climate is, “where heat is the dominant problem,
where, for the greater part of the year buildings serve to keep the
occupants cool” (Koenigsberger, 1973: 3). Koenigsberger (1973)
quoting Atkinson says tropical region has divided in to three major
climatic zones.
• Warm - Humid Equatorial Climate
• Hot – Dry Desert or Semi – Dry Climate
• Composite or Monsoon Climate
Generally warm humid climates are found in a strip of 15 degrees
either side from the equator. This includes regions like Southeast Asia,
Northeast Australia, Micronesia, Africa, and Central and South
45
America. Sri Lanka belongs to the warm humid equatorial climatic
region.
Other distinguishing characteristics include;
• The mean maximum air temperature is between 27 and 320 C. At
night time the mean minimum varies between 21 and 270 C. The
daily and annual ranges of temperature are narrow.
(Koenigsberger, 1973)
• High precipitation throughout the year. It exceeds 1500mm (60“)
of annual average rain and it will much higher in coastal regions.
(Emmanuel, 1993)
• High Relative Humidity. It is around 75% most of the time of the
year. Sometimes it exceeds even 90%.
• Low overall wind velocities, except during thunderstorms.
(The only strong winds are those of the northeast monsoon during
December and January, north of the equator. (Nieuwolt, 1968).
In coastal regions, the constant heating and cooling patterns of
the sea and land areas create regular sea breezes providing
regular air motion and mitigating the heat stress, mainly during
afternoon hours. Nights are often windless. In inland regions,
calms are frequent even during daytime, intensifying the thermal
stress caused by the combination of high temperature and
humidity (Givoni 1990).
• Predominance of diurnal processes as opposed to seasonal
ones. Days are almost equally long and climate processes are
regular. Emmanuel (1993) quoting Nieuwolt states that, due to
the limited variation in solar radiation, equatorial tropics do not
experience a seasonal variation.
In generally it can say that the average values of the climatic
parameters do not show significant changes. “These differences may
small in comparison to seasonal changes elsewhere, but tropical
46
inhabitants are keenly aware of such minute changes” (Emmanuel,
1993: 11). The sensitivity of the equatorial climate to micro-level factors
has important implications for architectural and especially urban
design, Sea coasts, valleys, basins and even tall, dense built elements
have appreciable effect on climatic parameters that are easily
noticed in this rather monotonous climatic region. (Emmanuel, 1993)
2.2 IMPACT OF URBANIZATION ON CLIMATE
2.2.1 URBANIZATION
Cities were originated as a response to the increasing needs of
man. Those urban centres were consists of few public buildings and
public open spaces. These urban centres have grown further with the
time. This urbanization process is clearly visible with the change in built
form in cities and the activities. Those were consists of public spaces,
public buildings etc. That was the nucleus of present urban centres.
These urban centres were tending to grow further with the time. This
urbanization process is clearly visible with the change in built form and
the increase of activities in those locations.
During the past two centuries, the urbanization process has
intensified rapidly. This is very significant in European countries because
of the industrial revolution. Emmanuel (1998) quoting Oke states that, in
hot-humid region this transformation will take place more rapidly and it
will do so in less than 50 years. This rapid urbanization process has made
a great impact on human life and environment. “The rapid urban
globalization has brought in its wake many hitherto unknown changes
to humans, other life forms and the physical environment” (Emmanuel,
1998: 5)
Urbanization has a dynamic relationship with the physical
environment. Due to its increased thermal capacity, lack of water for
47
evapotranspiration, and the “canyon effect”, there is a tendency to
exacerbate the negative effects of climate (Emmanuel, 2003). In
Addition, in the hot – humid regions, which urbanization took place in
such a pace, has not studied well for its microclimatic changes.
With this “ultra” rapid urbanization, the urban microclimate has
changed significantly. Therefore it has been a major factor in climate
conscious urban design since it has affected the outdoor thermal
comfort needs of man as well.
2.2.2 URBAN HEAT ISLANDS
The term heat island was first mentioned by Howard in 1833. He
has drawn out these conclusions from his study on urban climate of
London. (Emmanuel, 1993)
In general, urbanization has increased the ambient air
temperature of cities, than the surrounding rural areas (Moore, 1993).
This phenomenon is called as the Urban Heat Island Effect (UHI Effect).
48
Fig. 9 – Urban Heat Island
The boundaries of the heat island follow an urban air dome. The
horizontal temperature gradient, the rise from the periphery to the
centre, especially during the nights, is largest at the outer boundaries of
the urban area and flattens towards the centre of a built up area.
During the periods with light winds the heat Island is extended
downwind beyond the boundary of the urban built-up area. The height
of the heat island is rather shallow, extending upwards about three to
five limes the average height of the buildings and coincides
approximately with the urban & dome. Above this height the
differences between the urban temperature and the regional
temperature at the same height are very small. (Givoni, 1998)
Emmanuel (1993) states that, urbanization tends to aggravate
the negative effects of climate due to its increased thermal capacity,
lack of water for evapotranspiration, and the "canyon effect. This has
caused a thermal discomfort in equatorial is during the night time.
There are several different independent factors which affect the
urban temperature, especially near ground level, which contribute to
the development of the urban beat island. Traditionally it is cited that
the surface characteristics are the cause for urban heat islands.
However, now it is suggesting that the geometry of urban masses is a
primary contributor to the problem. The reason is building masses
retains the solar energy during the daytime hours and its release during
the night hours. It causes an increase in nocturnal temperature in the
city.
In addition, urban density which affects the urban climate is
always assists the creation of UHI. It causes modifications mainly in wind
conditions, air temperature, radiation balance, lighting etc. The
distribution of solar radiation is also varies within the density. Though the
availability of solar radiation is similar to rural areas, the distribution is
49
different. The higher density means that more radiation is absorbed by
building surfaces, where in rural areas it is mostly reflected.
Therefore, as an urban design tool urban geometry is more
important in promoting thermally comfort outdoors (Emmanuel, 1993).
Therefore, urban designers should look at this problem of equatorial
urban design to fulfill two requirements. First is to prevent the heat
build up in the in the city and second is to promote the convective
cooling during night time (Emmanuel, 1993).
2.3 RBAN DESIGN STRATEGIES
Tropical living is part indoors and part outdoors. Therefore, the
thermal comfort goals have to be different for outdoors and indoors. As
Emmanuel (1993) states the climate conscious equatorial urban design
should have two features. Those are prevention of heat buildup as the
day progresses and encouraging convective cooling at night.
“… reducing the possibilities of direct solar heating, long-wave
radiation with the sky, (i.e. reducing the sky patch visible from any
given point) and long – wave with the terrestrial surfaces (i.e. keeping
ground and vertical surfaces of an environment cool). All these goals
of course translate to one design strategy in the urban equatorial
areas: SHADING” (Emmanuel, 1993: 24)
Creation of shade in urban outdoors provides the ideal
environment for outside living, especially where large buildings draw air
down from the cooler conditions above the canopy (Hyde, 2000).
Other design strategies are also necessary. However, those should
facilitate shading to achieve best possible results. Givoni (1998) has
listed out the following urban design objectives for the equatorial
climates.
50
• Provide shade for streets and outdoor activities
• Enable natural ventilation for urban spaces
• Minimize flood hazard
• Provide rain protection for pedestrians
• Regulate rain water flow
Architecture is for people and it should facilitate people. As
mentioned in an earlier chapter urban space should be dense in form
and intense in activities (Prematilleke, 2000; Nikolopoulou, 2002).
Therefore, the above mentioned objectives are not enough to make
an urban space comfortable physically as well as psychologically. “The
activity patterns are considered necessary base, since urban living is a
set of interconnected activities”. (Emmanuel, 1993: 36) Therefore, the
climate conscious urban design strategies should consider the activity
patterns as well. The strategies should facilitate to generate activities.
Through comfortable outdoors.
2.3.1 DESIGN STRATEGIES FOR MITIGATION OF UHI
The primary goal in climate conscious urban design in equatorial
tropics is achieving shade. All the other strategies should introduce to
assist shading. The primary tool in achieving shade is urban massing.
The other approaches like vegetation also have a potential for
shading. Water bodies are enhancing the ventilating cooling during
night time. (Emmanuel, 1993)
The urban design tools can be drawn upon on the urban design
objectives which are mentioned earlier. The design tools can be
summarized as follows:
• Street Layout
• Building Density
• Building Morphology
51
• Height to Width Ratio
The above design tools are oriented towards achieving shading
by through urban form or urban geometry. Therefore, a critical study of
manipulating urban masses for complete shading is essential to create
liveable urban spaces.
2.3.2 SHADOW UMBRELLA
The future of climate conscious urban design is the equatorial
tropics lies in urban design initiatives. The rapid urbanization, high
density of population and altered urban climate has made the climate
conscious deign tools are crucial in tropics for humanized living.
(Emmanuel, 1993) Therefore, climate conscious urban form in the
equatorial tropics must be an “umbrella”, that shades it self, by it’s
three dimensional form.
The shade and shadow from large buildings can create
problems for open space in the city, during winter. During the summer it
is a relief indeed (Hyde, 2000). However, since Sri Lanka does not
experience such a winter season, shading is a relief through out the
year.
Shadow Umbrella is a shadow canopy that would shade an
entire outdoor area by its three dimensional volume. (Emmanuel, 1993)
It includes the buildable volume and areas surrounding the building.
(Emmanuel, 1993) The primary strategy in shadow umbrella is shading.
The shadow of a volume is depended on the following.
• Location
• Time / Day
• Orientation
• Building / Site Dimensions
52
The shading pattern of a volume is determined by the sun
angles. There are two types of sun angles. Those are Vertical and
Horizontal sun angles. These angles taken in to consideration when
locating urban masses to provide shading.
Shadow is the ultimate result of the presence of sun. Therefore,
location of the sun is very important in creating a shadow umbrella. In
the equatorial tropics, sun’s movement between the Topic of Cancer
and the Topic of Capricorn is felt minimally. Unlike in the temperate
regions the sun’s rays reach the tropics from all directions, including the
north and the south. That was during the northern-most solar exposure
(June 21 or there about) and the southern most exposure
(December21 or thereabout) (Emmanuel, 1993). Sun is located right
above Sri Lanka in April and September. Thus those two months are the
hottest periods of the year.
The daily pattern of solar heating essentially follows the sum,
starting from low in the morning, rising rapidly during the early day,
reaching the maximum shortly afternoon, gradually going down
Fig. 10 - Sun path diagram for 80 South latitude Source: Koenigsberger, 1974.
Fig. 11 – Eastern and Western
extremities
53
afternoon and declining after sunset. This whole cycle is too hot for
comfort. Therefore, it is much better to avoid the solar radiation as
much as possible.
Shadow or shading depends on the element to be shaded. In
this study, it will be public spaces like streets. The width of the street and
the height of the edge buildings determine the construction of shadow
and its effects on people. This shadow patterns could even dominate
the activity pattern as well.
In the case of a street, its orientation plays a major role. It affects
the whole street and the buildings as well. Because, a may cover the
street and another building. Then the shaded building will benefited in
terms of energy cost and the roof tops may be usable depending on
the time of shading.
54
C H A P T E R T H R E E
S H A D O W U M B R E L L A :
R E S E A R C H D E S I G N
55
C H A P T E R T H R E E
3.0 SHADOW UMBRELLA : RESEARCH DESIGN
This is a research initiative to ascertain the effect of urban geometry on
urban thermal comfort. The focus is on the use of building morphology and
other features to achieve complete shading as a major design strategy. The
final goal is to draw out urban design guidelines. Those will help to form the
built fabric of future cities by preserving the urban microclimates.
This chapter explores the possibilities of the use of urban building
geometry as a modifier of thermal comfort.
3.1 RESEARCH DESIGN
This research is based on data acquired by simulation. An existing
urban block will simulate and compare with the measured data.
Simulated data acquired by the modified situations will be
calibrated with the use of the above relationship.
3.1.1 SELECTION OF CASES & RATIONALE
As mentioned earlier, this study is on the effect of built masses on
outdoor thermal comfort. The case selected here is Pettah. Focus is on
the Prince Street and the 2nd Cross Street.
There are few other strategies, which could be used to achieve
thermal comfort in urban outdoors. Use of water bodies and
vegetation are the other two widely used strategies. Therefore, the
presence of water bodies and trees were avoided when selecting
56
cases. In Pettah, the effect of trees is zero because there are no trees
in the vicinity. Though there are water bodies, those are not much
significant in relation to the effect of built masses.
3.1.2 THE SITE
3.1.2.1 CONTEXT
Pettah is once a residential area which was turned out to a high
density commercial area today (Brohier, 1980). The harbour as a point
of goods transport and a gateway to Sri Lanka has given this area a
high commercial value. Domestic transport hubs like Fort railway station
and the central bus stand are drawing of thousands of people and
vehicles to this location daily.
Fig. 12 – Colonial Buildings. Still surviving despite
the
Fig. 13 – Dutch Museum
57
When considering about the land uses pattern, most of the lands
in this area are occupied by the commercial activities. Very few lands
has been used for public or civic activities such as museums, police
stations etc. (Dutch Museum & Pettah Police Station)
Because of the commercial activities and the public transport
hubs this location has became a very busy place during the daytime.
As a result, lots of illegal activities have emerged in and around this
area. This area has been a well-known place for illegal drugs, illegally
imported goods, underworld gangs, prostitution etc.
3.1.2.2 PHYSICAL CHARACTERISTICS
3.1.2.2.1 STREET LAYOUT
This area in Pettah has a very rigid street system which was laid
out by the Dutch rulers. This grid iron pattern streets running along two
major axes. Those are North – South axis and the East – West axis. The
streets are well defined by the building either side of the road. Since
these streets are not designed for motorized transport, the streets are
very narrow. Some parts of the streets are narrow as 3 – 4 m.
Due to the high building density alley ways are very common
with in these urban blocks. Those alley ways run deep in to the blocks
between streets. Most of them are not wider than 1.0 – 1.5 m.
3.1.2.2.2 THREE DIMENSIONAL FORM
The site is generally occupied by the medium to low scale
buildings. The average building height is about 2 - 3 floors. There are
few buildings which rise up to 5 – 6 floors. Most of the buildings are
rather old buildings and few modern buildings are coming now. In most
58
of the buildings, only the ground floor is used as the shop. Upper floors
are using either as stores or accommodation for the staff.
The building density is very high in this area due to the intensity of
activities and the high land value.
3.1.2.2.3 HEIGHT TO WIDTH RATIO
Since the low scale of built masses and the narrowness of streets,
the height to width ratio is relatively high. In some parts, the H/W ratio is
about 3 – 4. The H/W ratio affects the shading patterns and the solar
radiation. Therefore, this high H/W ratio has brought both positive and
negative effects on the microclimate.
3.1.2.2.4 DENSITY
In Pettah, the urban density is extremely high. Not a single open
space is seen other than the public streets. The only open space in the
area is the backyard of the Dutch museum. Therefore, it is viable to
checkout the possibility of having an open space as a thermal comfort
modifier. In addition, the spacing between buildings is also very low.
That also affects negatively to the microclimate of the area.
59
Fig. 15 - Unplanned developments causing disorderly urban environments
Fig. 14 - Pettah
60
3.1.3 METHOD OF STUDY
The study will have three phases. The first phase will be to find out
the relationship between simulated data and the actual data. In the
second phase, the existing built geometry will be modified and
simulate. In the final phase, urban design guide lines on building
geometry will be drawn out.
3.1.3.1 ORGANIZATION OF THE STUDY
Pettah is a unique urban context which could be seen in Sri
Lanka in terms of its built form and the activity pattern. Because of this
activity pattern and the physical characteristics, the whole length of
the street can be interpreted as continuous urban space. Despite the
differing public spaces, the whole street is a derivation of main areas.
Therefore, in selecting areas for simulation, patterns relating to almost
all situations across the site are considered.
Therefore, for the purpose of simulation two distinct places were
selected. The selected streets are running perpendicular each other.
One street is running North – South directions and other runs along East
– West direction. The modifications will be applied to both the streets.
First phase is an on-site measurement of temperature. This
will help to calibrate the simulate data and to identify the thermal
comfort patterns of the area.
Computer simulations of the existing selected area and
variations of the same. This includes shadow mapping and the
evaluation of thermal comfort.
61
Shadow mapping will be done on AutoCAD and thermal
comfort levels will be simulated on DEROB-LTH, which has the ability to
simulate the environments thermally.
DEROB-LTH
DEROB-LTH, which is an acronym for Dynamic Energy Response
of Buildings LTH, is a MS Windows based flexible simulation tool using a
RC-network for thermal model design. The program consists of 8
modules. Six of the modules are used to calculate values for
temperatures, heating and cooling loads. The calculations are
performed in a dynamic way for each hour during a specified period
of simulation. The calculations are influenced by climatic factors such
as outdoor temperature, solar radiation and the sky temperature.
Properties for the indoor climate of the building can be calculated
based on these simulated results. The properties are given as Predicted
Mean Vote (PMV, ISO 7730) index, Predicted Percentage of Dissatisfied
(PPD, ISO 7730) index and global – and direct operative temperatures.
One module draws a picture of the geometry of the building model.
DEROB-LTH can simulate buildings of arbitrary geometries. The
building elements can be described by one to five available shapes
and the geometrical model of the building is assumed to be placed in
a positive oriented Cartesian building coordinate system.
DEROB-LTH was originally developed at the Numerical Simulation
Laboratory of the School of Architecture of the University of Texas at
Austin. The DEROB-LTH modules are further developed to suit the local
needs at the Department of Building Science at Lund Institute of
Technology.
62
The out put from the DEROB-LTH is in form of either in
PMV or OT (Operative Temperature) or in PPD (Predicted Percentage
of Dissatisfied). Among these the most appropriate for the tropics is the
OT. Because, the other scales are developed for temperate climates
and the limits of discomfort is different.
Operative Temperature
The operative Temperature is the uniform
temperature of a radiantly black enclosure in which an
occupant would exchange the same amount of heat
radiant plus convection as in actual non-uniform
environment. In most practical cases where the relative
velocity of smaller that 0.2 m/s or where the difference
between mean radiant and air temperature is smaller
than 40C, the operative temperature can be calculated
with sufficient approximation as the mean value of air and
mean radiant temperature.
3.1.3.2 MODIFICATIONS
3.1.3.2.1 BUILDING HEIGHT AND STREET WIDTH
Initially modifications were done in accordance with the present
building regulations. And then it will be further modified to make a
thermally comfortable outdoor. When modifying building heights, a
maximum and minimum height was formulated. And also the rear and
front spaces, road frontage also should be finalised. The street width will
keep constant and the building height will be changed to adjust the
height to width ratio.
The street is an urban public space and it should be a “place
with life” to be habitable other than thermally comfortable. To fulfil
that, the sense of enclosure of a street is important. It will help to
63
perceive the whole street (both sides) a one entity. Otherwise, the two
sides will separate psychologically reducing the life of the street. And
also it affects the legibility of the street as well. (Bently et al.,
1985)Therefore, a minimum height to width ratio should be maintained
all along the street. Height/ width ratio should be at least 1:3 to sense
the enclosure. (Bently et al., 1985; Alexander, 1977; Lynch, 1960)
When considered about the present building pattern, most of
them has small road fronts and goes deep in to the block. There is no
spacing between buildings. Even the buildings are thin and tall, those
are seen as large volumes due to the zero space in between them.
The road width will kept constant. The maximum width of the
street is 6.0 m. Therefore, the minimum height of a building should be
approximately 2.0m, which is obviously possible to achieve.
According to CMRSP regulations the maximum building height is
determined by three major factors. Those are;
1. Zone
2. Plot Size
3. Road Width
Pettah belongs to the Central Business District which allows
unlimited number of storeys.
The CMRSP generally encourage development of large land
parcels in metro areas. The minimum plot size to put up a building is
150m2, which allows maximum 3 storeys. Therefore, in modifying the
plots were amalgamated to get the required height of the building.
Since the road width is constant (6.0m), only the low rise (2, 3 storeys)
and intermediate rise (4, 5 storeys) buildings are allowed.
3.1.3.2.2 ORIENTATION
64
Orientation of the street is a crucial factor in creating shadow
umbrella for the equatorial tropics, since it receives sun rays from all the
directions. The Selected streets were running perpendicular to each
other.
Those streets will be models for ‘East-West Running Street’ and
‘North-South Running Street’. In addition, the same streets will be
simulated for a direction in between the above two orientations.
3.1.4 ANALYSIS TECHNIQUES
This study is on the relationship between shading provided by the
built masses and the outdoor thermal comfort. Therefore, the Thermal
Comfort and the Shading Patterns have to be analysed primarily.
The comparison of on-site measured data and the simulated
data for the existing area will result an equation to calibrate
the future simulation data.
The First Case is modifications to the existing area will be done
according to the present building regulations. In the Second
Case it will be further modified to overcome the failures.
Variations will be done on the existing area with modifications
to the orientation and the height to width ratio. Each case
will have the following variations;
o North/South orientation > Tall buildings on one side
> Tall buildings on other side
o East/West orientation > Tall buildings on one side
> Tall buildings on other side
o Northeast/Southwest orientation
> Tall buildings on one side
> Tall buildings on other side
65
o Northwest / Southeast orientation
> Tall buildings on one side
> Tall buildings on other side
PMV and the OT simulated for the above situations will be
superimposed with shading patterns cast by each setting.
Temperature levels will be compared and analysed to
formulate design guide as the final outcome.
3.1.5 HYPOTHESES
Shading or shaded spaces have a positive effect on the
thermal comfort level of the people using those urban
spaces.
The manipulation of urban masses and increased height to
width ratio of the built mess increases the level of thermal
comfort.
The orientation and the ratio of building height to the width of
the streets considered can be consciously modified in order
to achieve thermally comfortable urban space.
66
C H A P T E R F O U R
R E S E A R C H & A N A L Y S I S
67
C H A P T E R F O U R
4.0 RESULTS AND ANALYSIS
4.1 BACKGROUND FOR RESEARCH
The first part of the study was to derive an equation to calibrate
the simulated data. Therefore, on site survey was carried out to
measure the actual temperature data.
After that the existing street was modelled in DEROB. The results
from the simulation were compared with the actual data to derive a
relationship between the two.
Simulation models were constructed in the parametric building
energy simulation programme called DEROB – LTH, which is capable of
analysing simulated environments thermally. However, DEROB is a
programme developed for indoor thermal simulations. Therefore, when
analysing outdoors, a dummy material was used. The following building
materials were used in modelling streets.
In addition, the three dimensional form of the streets were
simplified in accordance with the limitations of the software. However,
the general form of the street was kept as much as possible.
Name Conductivity
(W/mK)
Sp. Heat
(Wh/kgK)
Density
(kg/m3)
Concrete 1.7 0.24 2300
Reinforced Concrete 1.28 0.26 2100
Cement Mortar 0.93 0.29 1800
Brick 0.5 0.2 1300
Gypsum 0.22 0.23 900
Mineral wool 0.04 0.24 50
Air Space at 21 0C 0.024 0.280 1.201
Sand 0.4 0.24 1700
Earth 1.4 0.22 1300
Dummy Material 500 0.1 0.1
68
Table 1 – Materials used in DEROB
4.2 ON-SITE DATA MEASUREMENT
An on-site survey was carried out to measure the actual
temperatures of the site. The survey was done on 31st December 2003.
The temperature data was collected using a "hobo". Hobo was placed
inside a radiation shield to reduce radiation and at a higher elevation
to get the correct air temperature, avoiding the other factors such
body heat.
Fig. 16 – Hobo was placed inside a
radiation shield … and at
69
Time Actual
Temperature (0C)
Simulated Temperature
(0C) 0100 27.4 27.9 0200 26.3 27.5 0300 25.4 27.1 0400 25.0 26.8 0500 24.9 26.6 0600 24.8 26.7 0700 25.0 27.4 0800 27.8 28.7 0900 29.0 30.8 1000 31.7 32.1
1100 34.9 35.6 1200 36.4 37.8 1300 37.2 39.1 1400 37.4 39.1 1500 37.3 37.9 1600 36.9 36.1 1700 36.3 34 1800 35.5 31.5 1900 34.7 30.6 2000 33.6 30.2 2100 32.4 29.7
2200 31.1 29.3 2300 29.9 28.8 0000 28.6 28.4
Fig. 17 – Existing Street (Modelled in DEROB)
Table 2 – Measured and Simulated Data
70
Com
paris
on o
f Dat
a
y =
0.00
89x3
- 0.
9777
x2 +
36.
164x
- 41
3.35
R2 =
0.9
176
2022242628303234363840
2022
2426
2830
3234
3638
40
Sim
ula
ted
Da
ta
Measured Data
71
Malwatte Street
A scattered diagram was prepared to compare the simulated and
actual data (Fig. 18) and an equation was derived to calibrate the
simulated data in to actual data. The equation was,
y = 0.0089x3 - 0.9777x2 + 36.164x - 413.35 This equation was developed for the temperatures between 37.40C
and 24.70C. Therefore, this equation is valid only for that range. This
cannot be used to calibrate the data outside this range.
4.3 EXISTING CASE
Existing situation was analysed in terms of thermal comfort as a
starting point for the research. In this instance two existing streets, Prince
Street and the 2nd Cross street was modelled in DEROB to analyse the
thermal comfort levels.
72
Fig. 19 – Existing Streets
.3.1 SHADING PATTERNS
Shading patterns were obtained for the above two streets using
AutoCAD which is able to simulate the shadows according to the sun
path.
East – West Running Street North – South Running
Street
Shading Pattern at Shading Pattern at 10.00 a.m. 10.00 a.m.
Shading Pattern at Shading Pattern at
12.00 noon 12.00 noon
73
Fig. 20 - Shading Patterns for North – South Running Street & East –
West
Shading Pattern at Shading Pattern at
3.00 p.m. 3.00 p.m.
Shadows were simulated for 10.00 a.m., 12.00 noon and 3.00 p.m.
Streets are also in different orientations. The height to width ratio (H/W
ratio) is also somewhat higher in the north south running street (N/S Street).
In the morning (at 10.00a.m.), sun is on the eastern side with a
substantial altitude. Therefore, the N/S Street is completely covered by
shadow. But the shadow created by the buildings in the E/W Street is not
sufficient by to cover the street. This difference is clearly reflected by the
temperature levels.
The 1200 noon shade is not enough to cover either street. The
reason is sun is positioned right above the country during this period (05th
April). Thus, sun rays touch the earth almost from every direction.
Therefore, H/W ratio is powerless in this instance. Some other strategies
like shading devices, arcades, protrudes, should be tryout to achieve
complete shade.
74
At 3.00 p.m. also, N/S Street have complete shading than the E/W
Street. In the East – West Running Street the building height to width ratio is
low. Therefore, it is under sun for a substantial time. But, due to the slight
deviation from the exact east-west direction a narrow strip has been
shaded along the street. This strip has a good potential to develop as
commercial or pedestrian arcades.
4.3.2 THERMAL COMFORT LEVELS
Each of the street is modelled in DEROB to calculate the
temperatures and thermal comfort levels.
Fig. 21 – Shaded North – South
Street (At 3.00 p.m.)
75
The two selected streets have similar physical parameters.
However, the height to width ratio is slightly higher in the North-South
Street (2nd Cross Street). Other than that, the obvious difference is the
orientation.
As mentioned above, there is a difference between H/W ratios in
two streets. The effect of H/W ratio and orientation is more clearly
reflected in the thermal comfort levels in the street.
20
22
24
26
28
30
32
34
36
38
1 3 5 7 9 11 13 15 17 19 21 23
Time
Cor
rect
ed
Tem
pera
ture
North/South Street East/West Street
Fig. 23 – North - South Street
(2nd Cross Street)
Fig. 22 – East-West Street
(Prince Street)
Fig. 24 – Comparison of temperatures in two streets
76
Fig. 25 – Shadow Patterns and thermal comfort level an operative
temperature of E/W Street at 10.00 a.m.
The PMV diagram and the OT diagram a show that, in the non-
enclosed spaces (junction) the temperature is higher than the surrounding
area. The comfort level is also low.
77
Fig. 26 – Shadow Patterns, thermal comfort level and operative
temperature
of E/W Street at 12.00 noon
At 12.00 noon, the amount of shade is very low. But it creates a thin
strip along the southern edge of the strip. The effect of that modest shade
can be identified in the OT diagram. The width of the relatively low
temperature area is larger than the other side.
At this time also the temperature in the junction is approximately
1.5 -2.0 0C higher than the edge of the road. In the 1st Cross Street
junction, the temperature is higher than the other junction. The reason is
1st Cross Street Junction
78
streets at the other junction are defined by series of four storied buildings.
The shadows created by those volumes have lowered the temperature.
Fig. 27 – Shadow Patterns, thermal comfort level and operative
temperature of E/W Street at 3.00p.m.
The overall temperature has lowered with the going down of sun.
Unlike earlier cases in the day, the temperature at the 2nd Cross Street
junction has became equal to the rest of the street. But at the 1st Cross
Street junction, the temperature is about 0.5 – 0.75 0C higher than the
79
other areas. The high H/W ratio at the 2nd Cross Street Junction has made
the difference.
Fig. 28 – Shadow Patterns, thermal comfort level and operative temperature of N/S Street at 10.00 a.m.
Due to the complete shade of the street, the overall
temperature of the street is at a relatively lower level. The shadow
80
The overall temperature has risen up to almost 350C from the 29.50C
at 10.00 a.m. The shadow is covering a very small area of the street. That
small area of shadow is result of a five storey (H/W ratio – 3:1) building
volume. That reveals the presence of such a tall building will make the
environment more comfort than now.
Fig. 29 – Shadow Patterns, thermal comfort level and operative
temperature of N/S Street at 12.00 noon
81
Although the shadow has covered almost all the street, the
temperature is at 33.30C. The solar radiation at previous hours has
Fig. 30 – Shadow Patterns, thermal comfort level operative
temperature of N/S Street at 3.00p.m.
82
increased the temperature in the area and due to the canyon effect; the
heat has remained in the volume. Thus, the temperature has gone up.
Therefore, shading or cutting off the direct sunlight by built masses has a
substantial effect on the thermal comfort kevel of the street.
4.4 CASE ONE
The contemporary built form of Pettah does not comply with any
building regulations in the Colombo area. The average plot size is well
below the legal minimum size of a plot. When considered a building in
isolation, it does not make much difference to the urban microclimate.
But, these thin tall buildings form large volumes since they are located
very close to each other.
Therefore, a modified model of the street has developed for the
research by considering the general building height and massing pattern
of the street. The modifications were done in accordance with the
present building regulations formulated by the Urban Development
Authority (UDA) under the Colombo Metropolitan Regional Structure Plan.
Since the present plot sizes clashes with the regulations, the plots
were amalgamated to fulfil the requirement. Building heights were varied
according to the above guidelines. The maximum building height was
kept at 18.75m which allows up to 5 floors, including the ground floor. The
lowest building height was kept at 11.25m (3 floors), because due to the
high land value low rise buildings are not very economical. As a result the
H/W ratio was varying from place to place along the street. It ranges
between 1.5: 1 and 3:1.
3:1 2.5:1 3:1
83
Fig. 31 – Modified Streets & H/W ratios
4.4.1 Shading Patterns
East/ West Running Streets
Tall buildings on southern side Tall buildings on northern side
Shading Pattern at Shading Pattern at
10.00 a.m. 10.00 a.m.
Shading Pattern at Shading Pattern at
84
12.00 noon 12.00 noon
Shading Pattern at Shading Pattern at
3.00 p.m. 12.00 noon 3.00 p.m.
Fig. 32 - Shading Pattern for East/ West Running Streets
North/ South Running Streets
Tall buildings on eastern side Tall buildings on western side
Shading Pattern at Shading Pattern at
10.00 a.m. 10.00 a.m.
85
Shading Pattern at Shading Pattern at
12.00 noon 12.00 noon
Shading Pattern at Shading Pattern at
3.00 p.m. 12.00 noon 3.00 p.m.
Fig. 33 - Shading Pattern for North/ South Running Streets
Above figures shows the effect of the orientation on the shading
pattern of the street. Shading of East/ West running street is impossible due
to the sun path. However, sun is positioned either northern or southern side
most of the time during a year. Therefore, the street edges could be
shaded most of the time in a year.
In the other orientation the streets were shaded for a considerable
time. Even at around 12.00 noon, the edges are shaded. That shows a
good potential to create a human friendly zone along the building edge.
It could be a commercial or entertainment arcade, an overhang etc.
Northeast/ Southwest Running Street
Tall buildings on north-western side Tall buildings on south-eastern
side
86
Shading Pattern at Shading Pattern at
10.00 a.m. 10.00 a.m.
Shading Pattern at Shading Pattern at
12.00 noon 12.00 noon
Contd.
Shading Pattern at Shading Pattern at
3.00 p.m. 3.00 p.m.
Fig. 34 - Shading Pattern for Northeast/ Southwest Running Street
87
Northwest/ Southeast Running Street
Tall buildings on north-eastern side Tall buildings on south-western
side
Shading Pattern at Shading Pattern at
10.00 a.m. 10.00 a.m.
Shading Pattern at Shading Pattern at
12.00 noon 12.00 noon
Contd.
88
Shading Pattern at Shading Pattern at
3.00 p.m. 3.00 p.m.
Fig. 35 - Shading Pattern for Northwest/ Southeast Running Street
The above figures (Fig. 34 & Fig. 35) show the shadow maps when
the streets are diagonally located. Shadows cover the street diagonally.
Thus covers a larger area. A long building along the street casts a larger
shadow than a perpendicular building.
4.4.2 Thermal Comfort Levels
Fig. 36 – Modified building heights of the streets
89
20
22
24
26
28
30
32
34
36
38
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Cor
rect
ed Te
mp
E/W - Tall bldgs. on South E/W - Tall bldgs. on North
Fig. 37 – Comparison of temperatures in relation to the building height - East/ West Street
2022242628303234363840
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Time
Cor
rect
ed T
emp
N/S - Tall bldgs. on East N/S - Tall bldgs. on West Fig.
38 – Comparison of temperatures in relation to the building height - North/ South Street
90
20
22
24
26
28
30
32
34
36
38
40
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Time
Cor
rect
ed Te
mp.
NE/SW - Tall bldg. on NW NE/SW - Tall bldg. on SE
Fig. 39 – Comparison of temperatures in relation to the building height - Northeast/ Southwest Street
20
22
24
26
28
30
32
34
36
38
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Time
Cor
rect
ed Te
mp
SE/NW - Tall bldgs. On SW SE/NW - Tall bldgs. On NE
Fig. 40 – Comparison of temperatures in relation to the building height - Southeast / Northwest Street
Above charts shows the temperature levels in each of the
orientation when building heights are changed. Only the
Southeast/Northwest orientation has shown a decrease in temperature
91
with the change of tall buildings. In all the other orientations the change
of tall buildings does not make any significant change in temperature.
COMPARISON OF SHADOW PATTERNS AND OPERATIVE TEMPERATURE
Following figures shows the relationship between shade and the
comfort level of the street. The East/ West orientation is omitted here
because it does not have shade during the day. Therefore, thermal
comfort level is at a very low level. Other orientations are discussed here.
Fig. 42 – Shadow Patterns
and operative
temperature of N/S Street
Fig. 41 – Shadow Patterns
and operative
temperature of N/S Street
North/ South Running Streets - Tall buildings on eastern side
92
The above diagrams show relationship between shading and the
operative temperature. Among the three diagrams, OT distribution at
10.00 a.m. is the lowest and at the same time the whole street is shaded.
Fig. 43 – Shadow Patterns
and operative
temperature of N/S Street
93
However, at 3.00 p.m. the OT is relatively low, but higher than morning.
A dark strip can be observed along the eastern edge of the street.
That is a low temperature zone created by the shadows. That reveals
higher buildings or higher H/W ratio decreases the temperature level.
Those low temperature zones have the potential to be developed
as “human zones” or walkways.
North/ South Running Streets - Tall buildings on western side
94
Fig. 44 – Shadow Patterns
and operative
temperature of N/S Street
Fig. 45 – Shadow Patterns
and operative
temperature of N/S Street
95
These are almost same as the previous situation. But H/W ratio is
higher at the western edge. Therefore, the low temperature zone has
change to western side.
Fig. 46 – Shadow Patterns
and operative
temperature of N/S Street
96
Fig. 47 – Shadow Patterns
and operative temperature
of NE/SW Street at 10.00
Northeast/ Southwest Running Street - Tall buildings on north-western
97
In this orientation the temperature level at 3.00 p.m. is the lowest
Fig. 48 – Shadow Patterns
and operative temperature
of NE/SW Street at 12.00
Fig.48 – Shadow Patterns
and operative temperature
of NE/SW Street at 3.00 p.m. Fig. 48 – Shadow Patterns
and operative
temperature of NE/SW
98
among all three. The reason is tall buildings in north-eastern side cuts off
the sun rays and avoids the solar radiation.
In addition, low temperature zone has created by the tall buildings.
The temperature in that one is 3 – 4 0C degrees lower that the junction
area. Despite the shade, the temperature level in junction area is
comparatively higher than the other shaded area.
99
Fig.49 – Shadow Patterns
and operative temperature
of NE/SW Street at 10.00
Fig.50 – Shadow Patterns
and operative temperature
of NE/SW Street at 12.00
Northeast/ Southwest Running Street - Tall buildings on south-eastern
100
In this orientation, the shadows have given a good coverage to the
whole street in the morning. The tall buildings are cutting off the morning
sun and a good fraction of solar radiation. As a result a relatively good
thermal comfort level is maintained through out the day. (See Fig. 39)
Fig.51 – Shadow Patterns
and operative temperature
of NE/SW Street at 3.00 p.m.
101
Northwest/ Southeast Running Street - Tall buildings on north-eastern side
Fig.52 – Shadow Patterns
and operative temperature
of NW/SE Street at 10.00
102
Fig.53 – Shadow Patterns
and operative temperature
of NW/SE Street at 12.00
Fig.54 – Shadow Patterns
and operative temperature
of NW/SE Street at 3 00 p m Northwest/ Southeast Running Street - Tall buildings on south-western side
Fig.54 – Shadow Patterns
and operative temperature
of NW/SE Street at 3.00 p.m.
103
7
Fig.55 – Shadow Patterns
and operative temperature
of NW/SE Street at 10 00
Fig.56 – Shadow Patterns
and operative temperature
of NW/SE Street at 12 00
104
The above diagrams show the positive effect of the increasing of
built masses on the thermal comfort of the street. In almost every situation
there is a low temperature along the tall buildings.
Therefore, that strip easily could be made in to a commercial or
entertainment arcade to enhance the public use. Because, in the present
setting people are more attractive towards the shaded spaces. In most of
the times vendors are gathered around those spaces and people does
not have a place to walk. Therefore, introduction of arcades, overhang,
extended eaves could make more useable urban streets.
Fig.57 – Shadow Patterns
and operative temperature
of NW/SE Street at 3 00 p m
105
Since there is no spacing between the present built patterns in
Pettah, the street has become the ultimate public space. Therefore, the
streets should be thermally comfortable and useable for the pedestrians
to make Pettah a liveable city.
4.5 CASE TWO
Case two is a further modified version of case one. Since the case
one is done in accordance with the present building regulations, this case
is modified without considering the regulations. The intention is to check
the comfort difference between the two cases.
106
In the case two the building height was increased from one
floor. Thus the H/W ratio increases approximately from 0.5. In the
previous case, it was revealed that the used height difference
between two sides does not make much difference in the
comfort level. Therefore, in the case that option was omitted.
In addition, the East/ West running street was under sun
throughout the day. Therefore, that street was not considered in
the second case.
Fig. 58 – Modified Streets & H/W ratios – Case 2
4.5.1 SHADING PATTERNS
North/ South Running Streets
3:5 3:1 3.5:1
3:1 2.5:1 2.5:1
107
Shading Pattern at Shading Pattern at
10.00 a.m. 12.00 noon
. Shading Pattern at
3.00 p.m.
Fig. 59 - Shading Pattern for North/ South Running Streets
Northeast/ Southwest Running Street
Shading Pattern at Shading Pattern at
10.00 a.m. 12.00 noon
108
Shading Pattern at
3.00 p.m.
Fig. 60 - Shading Pattern for Northeast/ Southwest Running Street
Northwest/ Southeast Running Street
Shading Pattern at Shading Pattern at
10.00 a.m. 12.00 noon
Shading Pattern at
12.00 noon
109
Fig. 61 - Shading Pattern for Northwest/ Southeast Running Street
The shading patterns illustrated here reveals that diagonal
orientations are (Northeast/Southwest & Northwest/Southwest) more
effective than North/ South orientated streets. This phenomenon can be
clearly identified in the junction in the modified street.
In North/South orientation, good fraction of the junction is under the
sun. But in the two diagonal orientations the junction is completely
shaded at 10.00 a.m. and 3.00 p.m. Shading a junction is very vital in an
urban context like Pettah. Because, lots activities are happening at
junctions and as a result large number of people are gathering around
those. Therefore, thermally sound spaces at junctions will improve the
presence of people and activities.
4.5.2 Thermal Comfort Levels
110
Fig. 62 - Modified building heights of the streets
The models developed in DEROB was simulated to obtain the
modified thermal comfort levels. Those were compared with the same
orientation in the case 1.
North/ South Running Street
2022242628303234363840
1 3 5 7 9 11 13 15 17 19 21 23Time
Cor
rect
ed T
empe
ratu
re
Case 1 Case 2
Fig. 63 – Comparison of temperatures in the North/ South Streets This diagram shows a substantial decrease in temperature in the
morning hours (Between 10.00 a.m. and 1.00 p.m.). But, the solar radiation
took place during early afternoon increases the temperature levels in the
evening. Even in the late evening, the temperature is fairly high.
111
Northeast/ Southwest Runing Street
20
2224
2628
30
3234
3638
40
1 3 5 7 9 11 13 15 17 19 21 23Time
Cor
rect
ed T
empe
ratu
re
Case 1 Case 2
Fig. 64 – Comparison of temperatures in the Northeast/ Southwest
Streets
This orientation sperforms same as the previous orientation. But,
night time cooling is slightly better in this orientation. It will keep the night
time thermal comfort at a relatively better level.
Northwest/ Southeast Running Streets
2022242628303234363840
1 3 5 7 9 11 13 15 17 19 21 23Time
Cor
rect
ed T
empe
ratu
re
Case 1 Case 2
Fig. 65 - Comparison of temperatures in the Northwest/ Southeast Streets
112
This orientation shows a significant difference than the other
orientations. The reason is the tall buildings create a large shadow which
good fraction of it lies on the street and the opposite buildings. Especially
at buildings around the junction shades the whole open space at the
junction. It cuts off the direct sun rays during the late morning and early
afternoon reducing the solar radiation. Therefore, low radiant heating in
the morning results better thermal comfort throughout the day.
Comparison of Shadow Patterns and Operative Temperature
These images were prepared by superimposing the thermal
comfort diagram and the shading patterns. It clearly shows the positive
effects of shading on thermal comfort. The lighter areas of the comfort
diagram are the areas with low thermal comfort.
North/ South Running
113
Fig.66 – Shadow Patterns and operative temperature of N/S Street at 10.00 a.m.
Fig.67 – Shadow Patterns and operative temperature of N/S Street at 12.00 noon
114
Northeast/ Southwest Running Street
Fig.68 – Shadow Patterns and operative temperature of N/S Street at 3.00 p.m.
115
Fig.69 – Shadow Patterns and operative temperature of NE/SW Street at 10.00 a.m.
Fig.70 – Shadow Patterns and operative temperature of NE/SW Street at 12.00 noon
116
Northwest/ Southeast Running Street
Fig.71 – Shadow Patterns and operative temperature of NE/SW Street at 3.00 p.m.
117
Fig.73 – Shadow Patterns
and operative temperature of NE/SW Street at 3.00 p.m.
Fig.72 – Shadow Patterns and operative temperature of NE/SW Street at 3.00 p.m.
118
The general pattern of the distribution in this case is also, a relatively
more comfortable space along the tall building, slightly hot street and a
junction with high temperature. The level of temperature varies with the
time. Sometimes it exceeds the human comfort level, making the place
unliveable.
Therefore, the building heights could be increased to achieve more
comfort urban space. But then the high built masses retain heat and
make the uncomfortable outdoors during night time.
Fig.74 – Shadow Patterns and operative temperature of NE/SW Street at 3.00 p.m.
119
C O N C L U S I O N S
120
CONCLUSIONS
This study was mainly focused on creating probable patterns or
options for shading, in order to make the urban public spaces thermally
comfortable. The design implications and patterns are finding of the
research carried out on an existing urban setting and a modified version
of the same. The final outcome will be proposals for urban design
guidelines for the future use.
Following sub chapter discusses the findings of the research and the
implications of those on the urban space. In addition, it makes
suggestions and guidelines for the enhancement of the urban public
space and the thermal comfort of the space. It will facilitate a
comfortable, orderly and live urban space.
The study was carried out on the following hypotheses.
Shading or shaded spaces have a positive effect on the thermal
comfort level of the people using those urban spaces.
The manipulation of urban masses and increased height to
width ratio of the built mess increases the level of thermal
comfort.
The orientation and the ratio of building height to the width of
the streets considered can be consciously modified in order to
achieve thermally comfortable urban space.
121
DESIGN IMPLICATIONS
In urban deign, main tool for the designers to use is the 3D form of
the building. The research found out that the, height and the street width
can be handled positively to achieve a thermally comfortable urban
space.
In this study the building geometry was modified in terms of
orientation and H/W ratio. The design implications and design guidelines
could be drawn up for the modification of the above two parameters.
ORIENTATION
Orientation of a street is the very first design decision. Therefore, the
correct orientation should be selected to avoid the solar radiation.
East/ West Streets
According to the study, the orientation which should avoid is
East/West direction. At this orientation it is very difficult to cut down the
sun rays by the buildings alone. Even with higher H/W ratios (deep
canyons), it is difficult to create a shadow umbrella to facilitate the
thermal comfort level of the street. Therefore, oPther alternatives should
be sought to create shading.
122
Fig. 61 – shading devices above the street; it cuts down the
considerable amount of heat making the street
However, sun does not positioned “right above the head”
throughout the year. It happens only in April and September and those
periods are extremely hot. During the rest of the year sun is on either
northern or southern side. Therefore, the edges of the streets could be
shades.
External shading devices could be used in the building edges.
Overhangs, elongated eaves could be used in this case. It will
make the street edges a “habitable zone”. (See Fig. )
Under the present building regulations, projections to the street
are prohibited. Therefore, it would be positive move towards
thermal comfort if some kinds of overhangs are allowed, at least
on the streets with this orientation.
Introduction of arcades will facilitate pedestrian movement
along the street under the shade. These could be developed as
commercial arcades, spaces for entertainers or as sleeping
place for people during the night time.
123
P
However, the buildings on E/W orientated streets could be used
to shade neighbouring buildings. Then the roof tops of the
neighbouring building can be developed as usable spaces.
Those may not be public places but thermally comfortable,
habitable spaces.
In addition, other strategies such as landscape, vegetation could
be used to enhance the thermal comfort level of these streets.
North/ South Streets
Because of the sun path, the effect of shading in this orientation is
more direct and effective. Even lower H/W ratio is enough to provide a
substantial shadow umbrella. In Pettah area, H/W ratio of 1.5:1 will provide
adequate shading for the street, enhancing the thermal comfort of the
Fig. – Shaded spaces as sleeping spaces
Fig. – Shaded street edges
124
street. Therefore, narrow streets will be easier to shade. But, in terms of
land value low rise buildings are not economical.
Thermal comfort during the day time increases with the increase of
depth of the canyon or H/W ratio. The heat which collects among the
built masses does not escape easily doe to the less sky view. Therefore,
improve shading while ensuring adequate sky view appears to be the
basic requirement of urban design strategies for mitigating the negative
impacts of UHI effect. However, Pettah is a city which comes alive only in
the day time. It is almost dead during the night time. Therefore, the above
situation will not be a serious problem.
The two sides of the street receive sun on different times of the
day. Therefore, different activities could be introduced during
different times. Then the streets will be alive throughout the day.
H/W ratio should be increased. It will enhance the thermal
comfort level of the street. But the buildings should be located
parallel (located along the street) to the street. Unless, the
shadow is not effective.
Narrower streets have more shading possibilities. Then the streets
could be converted in to pedestrianized streets, since the
present level and the nature of activities do not encourage
motorized transport. Actually, these streets are not designed for
motorized transport (Brohier, 1980).
The required building height is not permissible by the regulations.
Therefore, it will be good to modify the regulations to achieve a
thermally comfortable urban space as well.
125
Northeast/ Southwest & Northwest/ Southeast Streets
Streets with this orientation do not make significant change in the
shading pattern of the street than the North/ South Street. Because of
being diagonal to the sun path, the shadow covers larger area.
Therefore, the building forms are not a significant factor. A shadow
created by the buildings which located parallel to the street and which
located perpendicular to the street covers almost same area.
Edge buildings can be used to shade the neighbouring
buildings. Then the energy consumption of those building
decrease.
Public open spaces such as urban squares could be introduces
along these streets because it receives substantial shading
through out the day.
Fig. – Pedestrianized Streets
126
HEIGHT TO WIDTH RATIO
It is obvious that, the shadow umbrella increases with the height of
the building. However, the most economical H/W ratio should be selected
to have optimum shadow to cover the street and to keep the thermal
comfort level of the street at a better level.
When considering on the microclimate in the Colombo city, it is too
hot for thermal comfort during most of the day time. Therefore, the
shadow umbrella should be enough to shade the street during the hottest
time of the day.
In the East/West orientated streets it is very difficult to achieve
shading by buildings. Other strategies should be implemented to
accomplish shading. But in the North/ south orientated streets an H/W
ratio about 1.5:1 – 2:1is enough to create a shadow umbrella. The ratio
above that figure is more comfortable during the day time, but it tends to
retain heat and enhance the urban heat island effect. Therefore, it will be
better to putdown a maximum limit to the building height.
The H/W ratio is important when the shadows are used to shade
other buildings. In addition, H/W ratio determines the comfort level of
open spaces such as squares. But in the Sri Lankan context, public squares
are not much popular. Most people use the streets & street edges as their
gathering space.
Under the present building regulations the building height is
restricted by zoning, plot size and the road width. But this is not very
positive restriction towards the thermal comfort due to the required ratio is
127
depended on the orientation of the road. In addition, the general thermal
comfort level of people varies with the regional climate (E.g. – Colombo
and Nuwara Eliya).
Therefore, when formulating building regulations the regional
climate and the orientation of the road or the street which the building
faces also should be considered. Thus the regulations will be unique to a
particular area. (E.g. Regulations for Pettah)
Moreover, in places like Pettah the minimum plot size rule is not
reasonable. To overcome that the plot size could be reduced and the
height and the spacing between buildings could be regulated. Then a
group of buildings will form the required volume.
These climate conscious urban design guidelines will not only make
orderly environments, but habitable and comfortable as well. The
comfortable street always attracts people. Thus make the urban space
live.
128
LIMITATIONS
The study was carried out within various limitations. Therefore, those
limitations should be taken in to consideration in implementing the
guidelines and strategies.
The study was based on the data measured in one single day of
the year. But, the average of long period data is more accurate.
Because, there may be accidental impacts on temperature.
The modifications were analysed by simulation. Thus, the
limitations of DEROB – LTH obviously affects the outcome.
Due to the limitations in modelling, the built masses were
simplified. Thus the impacts of slight changes and small details
were neglected.
DEROB is a tool designed for the evaluation of indoors.
Therefore, in simulating outdoors dummy materials were used.
It does not consider the ventilation and the effect of trees. The
study area is located close to the sea. Therefore, the wind
movement modifies the temperature levels.
129
DIRECTIONS FOR FURTHER STUDY
At present Sri Lanka is on the fast track to development. Thus, more
and more development will take place in the urban areas. The research
of this kind will be essential to make people friendly urban spaces.
The design of thermally comfortable urban spaces is about a
collection of various issues. Therefore future research work shall include;
Effect of the wind patterns on thermal comfort in urban
environments.
The same study could be carried out in a different area,
which has a different urban fabric.
Materials used in buildings and its effect on outdoor
thermal comfort.
130
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131
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