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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