ENERGY-EFFICIENT URBAN DESIGN GUIDELINES FOR WARM-HUMID CITIES: STRATEGIES FOR COLOMBO, SRI LANKA
Rohinton Emmanuel, Journal of Architectural & Planning Research, 12(1): 58 - 75, 1995
A b s t r a c t
This paper develops a set of energy efficient urban design guidelines for an equatorial tropical city (Colombo, Sri Lanka), on the basis of a survey of energy conserving urban design guidelines developed and applied principally in temperate regions. A total of twenty two urban design guide lines currently enforced in various U.S. cities and six from the U.K are analyzed. These address one or more of the following urban energy requirements: space conditioning, transportation and embodied energy needs. Problems related to excessive energy use in Colombo, Sri Lanka, are then identified by critically analyzing the "Colombo Development Plan" which legally binds all its urban development. Key factors analyzed are: Floor Area Ratio, plot size, building height, open space, waterfront development, and landscaping. Finally, a hypothetical proposal is made for Colombo. It includes eight design guidelines (amendments to existing legislation as well as new) for the reduction of cooling needs and three for the reduction of transportation needs. These are presented within two broad policy options: prevention of parcelling of urban land, use of existing railroad as a Mass Rapid Transportation system.
Introduction
Energy consumption in the developing world has grown tremendously over the past years. A world bank study reports that the developing world which accounted for 20% of the total global consumption in 1970, increased its share to 33% in 1988. (Imran, 1990) This trend is expected to grow at least for the first three decades of the next century.
Although many factors are cited as causes for the increase in consumption, it is generally agreed that urbanization in the region is the prime cause, particularly so in those areas where increasing income has resulted in greater demand for transportation and home appliances - especially space conditioning devices. The pattern of energy consumption in moderate-income developing countries (most of which fall in the warm-humid belt) suggests that urban design related decisions can have a significant impact on the end consumption of commercial energy. Such a reduction will inevitably lead to a healthier environment and ease the problem of pollution and congestion to a considerable degree.
It is in this context that the present study formulates energy-efficient urban design guidelines for warm-humid cities. The hypothesis is that guidelines can be devised to conserve energy, and that the most efficient of them are related to two urban energy needs in the region: transportation and space cooling. The paper is in two parts, a survey of existing energy-conscious urban design guidelines developed elsewhere (primarily in the U.S.) in order to develop concepts and, hypothetical applications to a warm-humid city, so as to illustrate their applicability. Colombo, Sri Lanka, is selected for this purpose and strategies are formulated on the basis of a critical analysis of its existing urban guidelines that regulates the city form.
Influence of Urban Design on Urban Energy Needs
The patterns of energy use differs among nations, yet certain commonalities exist in their urban energy needs. A comparison of energy use patterns between a developed country like the U.S. and a developing country like Sri Lanka shows that transportation and activities within buildings consume a considerable share of energy in both cases. (Table 1) The magnitudes however are different.
Table 1 - Patterns of Commercial Energy Consumption Sources: Erley & Mossena, 1980; Gardener, 1984 (quoted by Matthews, 1987); Amerasinghe, 1989
Urban design has an influence on energy needs for city transportation and space conditioning/lighting. The data in Table 1 can therefore be said to indicate that urban design has a vital role to play in urban energy need reduction, irrespective of the socio, economic context. Hence strategies developed in one climatic/economic context can be used to influence the conceptualizing of new strategies elsewhere. These of course need to be modified according to the climatic and socio, economic needs of the different situations.
A literature survey of the various energy efficient urban design strategies currently being implemented was therefore made in the hope of deriving principles of application for warm, humid regions. The main source of information in this endeavor was a survey carried out by the American Planning Association (APA) in fall 1979. This survey covered over 1400 local, regional and state planning agencies in the U.S., and involved an extensive literature review to identify communities that had adopted development regulations designed to save energy. Twenty two separate examples enacted by thirteen cities and communities in the U.S. were identified. (Erley & Mossena, 1980)
Reduction of Cooling Energy Needs
One of the severe problems with the urban energy consumption lies with the very form of the city. Development, which is usually piece-meal, is left to grow in a haphazard manner and there are no overall form determinants for most cities. An energy-conscious city form will help direct individual buildings and sites to be properly oriented, shaded or exposed as the need be, ensure ventilation, etc. Ralph Knowles' (1974) conceptual form for Owen's valley in California is an example of such an attempt.
Although no examples for an energy-conscious city form for the warm-humid region was found, some small scale strategies towards this end do exist. For example, a total of eleven examples were found by the above mentioned study specifically related to the reduction of space conditioning needs. They relate to one of the following urban design issues:
Table 2 gives a description and the date of adoption of nine of these regulations enacted by seven communities. (The other two strategies not listed here are for temperate regions) Table 2 Some U.S. Design Guidelines for the Reduction of Energy Needs for Space conditioning Source: Adapted from Erley & Mossena, 1980, pp 8 15.
Of those listed above, strategy #5 cannot be employed in warm humid climates as the underground temperatures in these regions are above 780 F which is beyond comfort range. (Labs, 1989, p 201) Similarly, the hedge and fence siting requirement by the city of Davis, California (#7) does not apply to warm-humid climates since this is a requirement in climates which also have a heating need. Hence the applicable cooling need reduction strategies will be as follows:
Reduction of Transportation Energy Needs
The way urban activities are organized, influences the way energy is spent in commuting between them. The greater the diversity of activities at a given place, lesser therefore will be the need for transportation. The solution lies in providing the right mix of activities that will reduce the energy spent on transportation. The goal is not to smoothen traffic, rather to reduce them. For, as Correa says, "ease of transportation is not an end in itself. Journeys always multiply to a point of clogging." (Correa 1989, p 73) At the same time, the efficiency of urban activities depends on the number of people served. In other words, density.
And density is not necessarily proportional to height. Correa shows that while height increases twenty fold, density increase is only four fold. (Correa, 1989, p 39) Indian Standards for ground floor housing = 50 families per Acre = 475 ft2 plot 5 story walk up apartment density = 100 families per Acre 20 story apartment block = 200 families per Acre Several theoretical attempts at defining low rise, high density development were found. (Correa, 1989, Soon, 1989, etc.) Most strategies related to residential or mixed use development. Correa drew from his experience in planning a new extension to Bombay, India. (Correa, 1989) In this model, he proposed a housing density of 638 per Acre or 63 households/4300 ft2 or 7 households/690 ft2.
This model is single storied development, but town house development with greater densities is also possible. (Lim, 1980) However, higher density dwellings are not always warranted. The use of alternative sources of energy sometimes makes higher densities unacceptable. For example, a density of 20 families/acre, is the upper limit, if bio mass is to be used as a source of energy. (Correa, 1989, p 106) Another strategy for dealing with density is to restrict plot sizes. In the Indian context, Correa (1989) suggested a medium size of 540 1080 ft2 in his new Bombay proposals and found that they were acceptable for both the poor and the affluent sections of the society.
Of the energy conscious urban design guidelines surveyed both in the U.S and the U.K., none came to as high densities as those proposed by Correa and others for third world cities. The most directly energy conscious approach encountered by the survey, at the urban scale, was Correa's proposal for New Bombay which had a system of mass transportation loops that permits smooth movement while preserving the self contained nature of individual clusters. (Fig 3)
However, many authors, including Correa agree that the most energy efficient mode of transportation is bicycle, closely followed by public transportation. (Illich, 1974, Matthews, 1985, Owens, 1986,1987, Correa, 1989, etc) As such the most energy efficient urban transportation strategy will be the encouragement of the use of bicycle.
The problem of riding bicycles in warm humid cities is posed by the high air temperature coupled with high relative humidity and traffic congestion. To encourage use of bicycles, therefore, shaded pathways exclusively designated for bicycles can be provided. In addition to the overall strategies mentioned above, several neighborhood and intra urban scale strategies were also encountered. These relate to one of the following:
Table 3 Some U.S. Urban Guidelines for the Reduction of Transportation Needs Source: Erley & Mossena, 1980, pp 8 20.
In addition to the above mentioned aspects of energy conservation (city form, density, cooling need and transportation need) the APA study also found regulations that reduce the embodied energy requirements (i.e. energy spent in the construction of urban elements). These usually take the form of reducing street widths. Three examples (Windsor, Connecticut; King County, Washington; and Davis, California) were reported by the above study.
Outstanding Issues
If the design guidelines are to be effective in terms of reducing cooling needs, they must ensure that buildings and not just sites are oriented properly. At the urban scale, it is easier to control site orientation than building orientation without infringing too much upon individual designers' design choices.
In the warm humid zone, ventilation plays an important part in thermal comfort. However, it is difficult to set design guidelines for ventilation, as it depends on micro climatic factors like topography that are very site specific. In order to be effective, regulations for reduction of cooling needs must be flexible, like trade offs between orientation, window size etc. (Erley & Mossena, 1980, p 30)
Landscaping regulations need to be specific about type of trees, etc. It is necessary to develop a concise table of information specifying common warm humid zone trees and their environmental qualities. (area of shading, resistance to wind flow, etc) Similarly, guidelines related to shading need complex formulae for calculation. In order to simplify the process, it is necessary to develop shadow tables that specify the amount of required shading at different orientation for a given location. Conceding that these and other unanswered issues exist, it is still possible for us to attempt to employ the principles enumerated thus far to a warm, humid city which is the main focus of the study.
CASE STUDY: COLOMBO, SRI LANKA ANALYSIS OF THE "COLOMBO DEVELOPMENT PLAN"
Before the principles and strategies for energy conscious urban design guidelines could be applied to the city of Colombo, it is necessary to identify the problems with the existing development model. Present developments in Colombo are governed by a legal document called "City Of Colombo Development Plan" published by the Urban Development Authority of Sri Lanka, empowered by an Act of Parliament (Law No. 41 of 1978) to plan, regulate and implement development in urban areas of Sri Lanka. This publication outlines the development regulations applicable to the city of Colombo. The following analysis is intended to highlight the deficiencies in Colombo's city planning in terms of energy use. Textual references are to the above document.
General Characteristics of the City
The physical structure of Colombo is similar to many of the colonial port cities. The Fort was the focal point around which were established residential areas of white settlers and residences of local inhabitants some distance from it.
In the course of time, Fort became the financial and Government center and Pettah (an outlying area adjacent to the old Fort) a center for retail and wholesale trade serving the needs of a growing city and entire Sri Lanka. Industries were established close to this area where the railway was also located. New developments were guided by the communication routes and the terrain. (Vol I, p 8)
Colombo is hemmed by marshes on the East, Kelani Ganga, the most voluminous river in Sri Lanka on the Northeast, and the Indian Ocean on the West. The development pattern has been an elongated North South linear model along the major highway to southern Sri Lanka. (Fig 4) While the central part of the city houses parks and spacious bungalows, the edges, particularly eastern and south eastern parts, are dominated by shanties and slums.
Specific Characteristics of the City Sub divisions
The city of Colombo is divided into fourteen planning units, covering a total extent of 9224 Acres (14.4 sq.miles). The specific characteristics of each sub divisions are as follows.
Table 4 Specific Characteristics of Colombo's Sub divisions Source: Adapted from Colombo Development Plan, Table 2.1, Vol I, pp 5,6.
Planning Unit Extent(Acres) Character Fort 442 Central Business District (CBD) and shopping area Kochchikade 394 Old residential area with considerable slum housing Maradana 529 Old residential area and now an extension of CBD Kollupitiya 719 High and medium income residential area with considerable commercial development. Also contains sea frontage Mattakuliya 939 Old residential area now intruded with warehouses Kotahena 420 Old residential area with considerable slum housing Grandpass 612 Commercial, industrial and low income houses surrounded by marshes Dematagoda 704 Commercial, industrial and low income houses surrounded by marshes Borella 385 Middle income residences and secondary shopping Cinnamon Gardens 849 High income residences and embassies, with many civic buildings Bambalapitiya 588 High and middle income residential area with considerable shopping zones. Also has sea frontage Wellawatte 828 High and middle income residential area with considerable shopping zones. Also has sea frontage Narahenpita 874 Medium income residences and public activities Kirillapone 941 Medium income residences interspersed with slums Total Area 9224 Population and Residential Density The city of Colombo had an overall population of 585,776 in 1981 (last year of official Census). This worked out to a gross density of 157 persons/Ha (64 persons per acre). However, a much higher residential density prevails in all the planning divisions.
Table 5 Population Distribution in Colombo Source: Adapted from Colombo Development Plan, Table 3.3, Vol I, p 13.
Planning Unit Population Residential Density Persons / Acre Overall Density Persons / Acre Fort 17,029 - 38 Kochchikade 80,045 484 204 Maradana 47,997 286 91 Kollupitiya 47,432 236 66 Mattakuliya 59,027 139 63 Kotahena 34,052 197 81 Grandpass 54,018 273 88 Dematagoda 58,854 224 84 Borella 27,849 154 72 Cinnamon Gardens 16,738 58 20 Bambalapitiya 25,122 54 43 Wellawatte 47,163 81 57 Narahenpita 28,114 79 32 Kirillapone 42,336 60 45 Total City 585,776 140 64
Land Use Pattern
Colombo is predominantly a residential city; residences occupy 52% of its developed area. Surprisingly, the second largest land use in Colombo was transportation.
Table 6: Land use Pattern in Colombo Source: Adapted from Colombo Development Plan, Table 3.2, Vol I, p 10
Land Use Extent (Acres) % of Developed Area % of Total Area Residential 4,169 51.8 45.2 Commercial 497 6.2 5.4 Industrial 373 4.6 4.0 Public & Semi Public 1,149 14.3 12.5 Transportation 1,507 18.7 16.3 Open Spaces 351 4.4 3.8 Developed Area 8,046 100.0 87.2 Undeveloped Area 936 - 10.2 Water 242 - 2.6 Total 9,224 - 100.0
The CBD, comprised of old colonial buildings and the congested Pettah area, accommodated a daytime population of 550,000 persons in 1980 while the total residential population of the city (in 1981) was 585,776. (Vol I, p 11) Colombo had a considerable percentage of marshes on its eastern fringe. However, by 1981, this shrunk to 936 acres. Many private developers and some state agencies are currently in the process of reclaiming these spaces. (Vol I, p 16)
Energy consuming Features of Colombo
Analysis of Urban Design Guidelines of Colombo
The following urban design ordinances were identified as potential energy consuming regulations and selected for detailed analysis. Floor Area Ratio (FAR) Plot Size Building Height Regulations Overhangs and relationship to the street Landscaping
FAR: FAR is defined as total built square footage divided by plot size. The average FAR for the city is 2.0, with most areas having a very low figure of 0.75 1.25. Only the CBD is allowed to have a density of more than 2.5. In other words, a low rise, spread type development is encouraged by the development plan.
Plot Size: The minimum permissible plot size is 6.5 perches (1770 sq.ft). The law permits a maximum of 80% plot coverage for residential buildings. It also specifies that plots be a minimum of 20 feet deep. A combination of these regulations thus yield a situation similar to the following: Plot size = 1770 sq.ft Buildable area (80%) = 1416 sq.ft Av. plot dimensions = 60 feet X 30 feet Rear space clearance = 10 feet Road reservation = 10 20 feet Therefore actual building size = 60 X 10 15 feet. (Fig 5) The resultant architecture is a wall to wall strip development, with narrow backyards usually partitioned by high parapet walls for reasons of privacy, and not street related. (Fig 5 Strip Development approximately here.) A further regulation restricts the projection of roof eaves and balconies into streets. (Only up to 3 feet is allowed) Therefore the buildings are usually blunt to the street with little possibility for lighting and ventilation from the streets even though they are street oriented. (Fig 6) In a residential city, such a form does not encourage pedestrian movement due to its thermally uncomfortable nature. (Fig 6 Street Oriented, but not Street related approximately here.) Open Spaces: The law requires that all sub division plans of one acre or more in extent include a minimum of 10% open space. Since most developments are much smaller than one acre due to high land value and scarcity, sub divisions are approved with little or no open spaces. Furthermore, there is no provision for common amenities like parks and play grounds.
Building Height: The maximum height of buildings is restricted to 50 feet. However, lighting plane regulations impose a 63.50 restriction over and above this. With small plot sizes, the usual height therefore is much less than 50 feet. (Fig 7) Additionally, the 63.50 light plane also brings in enormous quantities of light onto the building. (63.50 light plane was developed for the temperate zones where the intensity of the sky dome is about 1/5 of the tropical sky) (Fig 7 "Light Plane" approx. here.) Landscaping: There is no regulation requiring landscaping be an integral part of the design.
Summary of Energy related Problems
On the basis of energy needs of urban areas identified earlier, the following relationships could be made: Problem # 1, 3, 4, 7, 8 & 10 > Cooling Need Problem # 2, 5 & 6 > Transportation need
Energy Conscious Design Guidelines for Colombo
Among the ten broad problems identified above, two basic strands could be detected: Increasing fragmentation of land, leading to increases in both cooling and transportation needs; under development of existing mass transportation facilities, straining the transportational resources of an essentially residential city.
Design guidelines, on the other hand, are often specific measures that essentially deal with design problems at a smaller scale. Effective energy conservation however, must begin at a larger scale. The following policy options could be the basis for significant energy conservation in Colombo.
Within such an administrative and political framework, the following specific design guidelines can promote energy efficiency. Eight guidelines for the reduction of cooling needs and four for the reduction of transportation needs are discussed in this regard.
Guidelines for the Reduction of Cooling Needs
1 Site Orientation "New developments to have a predominance of North or South facing blocks." Site Orientation is the orientation of the line connecting center of building line with center of rear space line. (Fig 8) (Fig 8 Site Orientation approx. here.) Examples of similar guidelines enacted: Sacramento, CA, Dade County, FL Boulder, CO. (While these regulations ensure solar access, the proposed guideline ensures shading, since the climatic need in Colombo is cooling only) Ideal orientation = North or South Permissible orientation = plus or minus 50 North or South (after Olgyay, 1963)
2 Seaside Development for Ventilation "New seaside developments to be 450 to the sea". Present development is perpendicular to the sea, thus blocks are parallel to sea. Thus micro-climatic wind patterns from sea are not made use of. (Fig 9) (Fig 9 Site & Street Layout for Air Movement approx. here.)
3 "Stepped" Massing Around Water Bodies "Encourage a "stepped up" growth around water bodies". Since Colombo is in the "doldrums" (no wind periods) twice yearly, (Koenigsberger, et al. 1974) maximum advantage must be made of local factors enhancing wind movement. (Fig 10) (Fig 10 "Stepped form" development around water bodies approx. here.)
4 Ring road Around Water Bodies "Create ring roads close to water bodies so as to prevent development around them". Roads located sufficiently away from lakes etc, encourage development between roads and water bodies. Such water bodies become backyards of development, diminishing their thermal comfort enhancing potential. (Fig 11) (Fig 11 Ring road Around Water Bodies approx. here.)
5 Street related Development "Prohibit high parapet walls on the roadside of new development". In climates where air movement is vital for thermal comfort, every attempt must be made to ensure adequate speed of air. Parapet walls cast a wind shadow of about 5 times their height. (Koenigsberger, et al., 1974) Residential development may be allowed a small wall for the sake of privacy. (3 feet or less) (Fig 12) (Fig 12 Street related Development approx. here.) 6 Shaded Walkways "All street reservations to be shaded". Urban areas are known to have a substantially higher temperature than the countryside. ("heat island" effect) One way to reduce thermal discomfort in cities is to minimize radiating surfaces with shading. Trees, arcades etc could be used for this purpose. (Fig 13) (Fig 13 Shaded Walkways approx. here.)
7 Steep"Light Plane" "Permit narrower courtyards and spaces between buildings". The present requirement of 63.50 brings in an unwanted amount of light from a very bright tropical sky. Steeper light planes are therefore suggested. (Fig 14) (Fig 14 Steep "light Plane" approx. here.)
8 Arcaded Commercial Development "Arcades to be incorporated in all new commercial developments". An interface between buildings and streets creates a climatic barrier to the building as well as encourages people to walk between them. (Fig 15) Most activities in the tropics can happen outdoors. (See Correa,1989, for a discussion on "usability co efficient" which is a product of a fraction of activities that can be performed outdoors and a fraction of time of year when such activities can occur outdoors) (Fig 15 Arcaded Commercial development to be here.)
Guidelines for the Reduction of Transportation Needs
9 Traffic Nodes of Colombo "Create traffic nodes around railway stations and close the roads directly connecting them to private automobile traffic". If the railway could be developed as a mass transportation system, buses could take passengers from exit points on the railroad, making the entire city accessible by public transport. (Fig 16) Since private cars consume the largest amount of energy spent on transportation, they should be given least priority. (Fig 16 Traffic Nodes approx. here.)
10 Mixed Land use Development "Permit mixed use development in all sub divisions". Extensive commercial and business activities in CBD create strong directional traffic to and from it in mornings and evenings. Instead of encouraging residential areas as the primary land use in many subdivisions, mixed development should be allowed in all sections of the city, reducing the need for travel.
11 Bicycle lanes "All new sub divisions to incorporate bicycle lanes, preferably shaded". Bicycles are the most efficient form of urban transportation. Every effort therefore must be made to ensure its use. Separate lanes and in tropical conditions, shaded areas, are essential for this purpose.
Conclusion
It is thus possible to derive principles from a different climatic milieu and still apply them to warm humid climates. However, certain questions still remain unanswered regarding the implementation of such guidelines.
Although the "energy crisis" is with us for nearly two decades and a substantial body of knowledge related to structural energy efficiency was consequently developed, very little was actually implemented. For example, the APA study quoted above could find only 22 such examples from 13 communities among the 1400 communities surveyed. The problem seems not one of understanding the importance of energy saving but wider socio-political anomalies. Owens (1987) suggested the general contempt for planning, vested interests particularly in the transportation sector, and the slow rate of urban renewal as possible causes.
Another objection frequently raised with respect to the implementation of energy efficient guidelines is the necessity for such an endeavor. It is sometimes argued that since energy prices will continue to be cheap, designers should concentrate on areas other than energy efficiency. While this may be true, we must also remember that the rationale for energy efficient design is not so much the need to conserve energy per se, rather reduction in energy consumption for the ecological health of the whole planet. As we mentioned earlier, the warm-humid region with its teeming energy-hungry millions will continue to consume more energy. And the ecological consequences of such high consumption are beyond our collective wisdom. (Wasted energy almost always leads to pollution and the effects thereof.) The future direction of energy efficient urban guidelines should perhaps be guided by this concern for ecological health of the earth, and not just by quantitative gains in energy efficiency.
References
Related References:
Acknowledgements:
The author wishes to thank Prof. Wayne Attoe, Graduate Program Coordinator, School of Architecture, Louisiana State University, whose critical comments and encouragement from the inception helped finalize this paper.
Autobiographical Sketch
Rohinton Emmanuel is a Lecturer at the Faculty of Architecture, University of Moratuwa, Sri Lanka. He is a graduate of the same University where he did his M.Sc. in Architecture. His research interests focus on thermal comfort in the equatorial tropics, with particular emphasis on responding to the urban heat-island, and energy-efficient urban design. He is currently a doctoral student at the College of Architecture, The University of Michigan.
Return to Publications
Return to Resume
Return to Rohinton
Emmanuel's Home Page