UDC3: Impact of Urban forms on comfort I : tropical and arid climate cities
Evaluation of the effect of densification of the built environment on outdoor thermal comfort in warm-humid Dar es Salaam, Tanzania
Lund University, Sweden
Many cities in the tropics suffer from increasingly higher temperatures due to both global and urban warming. Often the thermal conditions are worsened by poor urban design including lack of shade and poor ventilation. Moreover urban regulations are often poorly adapted to the climate and there is often a lack of vegetation. In Dar es Salaam, Tanzania – which has one of the highest urbanization rates in the world mainly occurring as horizontal growth – the thermal conditions are poor, especially in the afternoon during the period October to April (Ndetto and Matzarakis, 2013). In response to this, the urban planning authorities act to densify the city, especially the central areas. This is done through redevelopment schemes which allow considerably higher buildings than previous regulations. The main aim of this paper is to evaluate the effect of the proposed densification of the built environment on microclimate – especially wind speed, solar exposure and shade – and outdoor thermal comfort. The aim is also to suggest how the proposed redevelopment schemes could be modified in order to improve thermal comfort. The study is mainly based on numerical simulations of the influence of parameters such as building form, materials, shading devices and vegetation using the model ENVI-met. This study will provide recommendations to urban planners and designers in Dar es Salaam on how to design thermally comfortable, high-density urban areas. Recommendations will include advice on street orientation, height-to-width ratios of urban canyons, building forms, type and positioning of vegetation and type of surface materials.
The role of urban design in enhancing the microclimate and thermal comfort in warm-humid Dar es Salaam, Tanzania
Lund University, Sweden
Due to the complexity of outdoor environment, urban design patterns considerably affect the microclimate and outdoor thermal comfort in a given urban morphology. Parameters such as building heights and orientations, spaces between buildings, plot coverage, etc influence the microclimate in terms of solar access, shade, wind speed and direction. In warm-humid Dar es Salaam, the consideration of microclimate and outdoor thermal comfort in urban design has received little attention although the urban planning authorities try to develop the quality of planning and design. The main aim of this study is to investigate the relationship between urban design, urban microclimate and outdoor comfort in four different areas in the city of Dar es Salaam, during the wet and dry seasons. This investigation is mainly based on microclimate simulations using ENVI-met and different existing urban morphologies are climatically and thermally studied including low, medium and high rise buildings. Parameters such as Mean Radiant Temperature (MRT), wind speed and Physiological Equivalent Temperature index (PET) are presented as thermal maps to highlight the strengths and weaknesses of the existing urban design in the city. The study illustrates that the areas with low-rise buildings lead to higher MRT values than the areas with high-rise buildings. The results also show that the use of dense trees helps to enhance the thermal conditions, but it might negatively affect the wind ventilation in the outdoor spaces. This study provides a set of guidelines on how to develop the existing situation from microclimate and thermal comfort perspectives. Such guidelines will help architects and urban designers to increase the quality of outdoor environment and demonstrate the need to create better urban spaces in harmony with microclimate and thermal comfort.
AMONG WINDS, WATER BODIES AND URBAN ELEMENTS
Federal University of São Carlos, Brazil, Brazil
This study analyses the interaction influence of winds and water bodies in the thermal conditions on an unoccupied margins of an urban area. Two temperature and humidity sensors were placed on the two opposite margin of a water reservoir in São Jose Do Rio Preto, Brazil. One, placed on the east margin, and another one on the west margin, to register the differences in between temperature and humidity according to the changes of wind speed and direction. The dates were collected on site in August 2011, compared with dates of a Meteorological Station from CIIAGRO and with Satellite images of CPTEC. After the site monitoring, three different urban occupation models were prepared with the software Envi-met 3.1 in each margin of the water reservoir. So, the created urban scenarios were made to demonstrate how to optimize the natural resources in refreshing the area and to distribute the humidified ventilation through urban space. During the warmest and driest period, the maximum difference of temperature was 1,77°C. It was verified that the wind and water combination kept the east margin average 0,5°C colder and 0,4 g/m³ more humid than the west one. The microclimate urban maps produced by the simulation process could help to predict the better solution of urban design and also indicated the behavior of urban temperature, humidity and winds, presenting the results graphically over the urban area. This study, firstly, indicated that water bodies may increase the stability of the temperature in the nearest in different urban settings. Secondly, the Envi-met 3.1 software demonstrated to be an able tool to estimate quite precisely the effects in the microclimate of possible urban interventions. Thus, water bodies influence their surroundings and indicate to the planners how the effects of environmental resources can produce more pleasant cities.
Climate-Friendly Urban Design Process in Old Towns alongside the Persian Gulf, Case Study: Bushehr
1University of Applied Science, Tehran, Iran; 2Tarbiat Modares University, Tehran, Iran
The northern side of Persian Gulf with hot and humid climate has a rich treasure urban development during history. Bushehr is one of big cities in the region that a context for learning traditional urban design according to climate consideration. Especially in Bushehr old town a hierarchy of climatic design can be seen from site selection to building details.
During these two decades, urban design projects have been started in the old town to provide a better context for urban life. In most of these projects, climate consideration of urban development has not been emphasized as a key factor. So, climatic function of urban spaces in the old town has changed and climatic comfort has decreased in urban spaces.
This research tries to introduce a climate friendly process for urban design projects in Bushehr old town. Thus, as a first step traditional climatic design principals in the old town has been discovered and analyzed base on scientific literature review. Then, main urban design projects have been evaluated based on climatic consideration. Finally, a climatic friendly process has been suggested to enhance the environmental quality of the old town in urban regeneration projects.
Research findings demonstrate that street directions, H/W ratio of streets, street profiles, form of urban plazas, network of urban spaces, building facade designs, architectural spaces design and architectural details in the old completely planned according to climate situation. Especially to have maximum wind in urban and architectural spaces some initiatives can be seen like site selection of city as a peninsula according to local and regional winds, special form of sky line to disturb regional wind, special form of urban spaces, tall building alongside urban spaces higher than other building, direction of main streets to conduct wind into city, section of alleys to absorb maximum wind and some specific architectural elements and space like Shenashir, Tarmeh and Boun.
Three urban design projects have been selected in different type and different part of old town for evaluation. First project is a street from coastline to a neighborhood center. Second is a plaza and third is a pedestrian street at the edge of old town and new urban development part. The attention to wind ,shadow and thermal comfort in this spaces have been analyzed. Final evaluation show less attention to climatic design consideration in planning, design and implementation.
So, based on these results and different models of urban design process, a unique climate-friendly urban design process has suggested for urban design projects in old town of Bushehr.
Keywords: Bushehr, Urban Design, climate-friendly process, design principals
Application of airborne LiDAR and thermal Infrared technologies for the assessment of human biometeorological conditions in urban areas
1Department of Architecture, National Cheng Kung University, Tainan, Taiwan; 2Faculty of Environment and Natural Resources, Albert Ludwigs University, Freiburg, Germany
The rising global temperature contributes to a strong impact on urban thermal environment and outdoor thermal comfort. Although the existing satellite telemetry methods are convenient to display geographical information. The detail distributions of 3-dimentional radiation properties of the complex urban environment cannot be estimated accurately due to the low resolution and lack of vertical information. Hence, satellite telemetry methods cannot provide enough information concerning biometeorology conditions in urban areas.
This research applies an innovative method to observe urban thermal environment by coupled airborne LiDAR and thermal Infrared (TIR) technique combined with synchronous climate measurement in ground level. Banqiao District of New Taipei City, one of the highest developed areas in Taiwan, is selected for the survey area. Regarding the airborne survey, the use of high-resolution LiDAR, with 1m*1m resolution, could be imaging from scanning terrain and surface obstacle exploration. Building height, total floor area, vegetation forms and height can be also identified. For the TIR, with 0.5m*0.5m resolution and 0.1°C accuracy, the surface temperature and emitted radiation from horizontal and vertical surfaces can be also estimated. In the screen level measurement, air temperature, vapor pressure, surface temperature, wind speed and direction are all measured simultaneously in the streets and open spaces in survey areas. By combining those three kinds of information through GPS positioning system, the mean radiant temperature (Tmrt) estimated by various approaches can be calculated and compared.
The results indicated that Tmrt estimated by the LiDAR and TIR are highly in accordance with the value measured in the ground level. Furthermore, the Tmrt and Physiologically Equivalent Temperature (PET) are calculated and displayed as a distribution map. The hotspot of the survey area, which comprised high density building and high amount of anthropogenic heat, can be identified through the map. The analytical result reveal that the use of coupled LiDAR and TIR technology approach will be contributed to understand the urban human biometeorological conditions quickly and accurately.
Holistic Method on Performing Microclimate Analyses of an Urban Area in the Tropics
National University of Singapore, Singapore
The world has experienced unprecedented urban growth in the last century. For the first time in history, more than half of the world population were urban dwellers in 2008. United Nations estimated that by year 2030, up to 5 billion people will live in urban areas, or 61% of the world's population.
Consequently, cities are growing towards megacities with higher density urban planning, narrower urban corridors and more high-rise urban structures. Increasing urbanization causes the deterioration of the urban environment, as the size of housing plots decreases, thus increasing densities and crowding out greeneries. Within the built environment at micro-scale, buildings and vegetation influence the incident solar radiation received by urban surface.
Within this context, urban planners have the responsibility to create not just livable and aesthetic cities, but also environmentally friendly to promote a sustainable society. Hence, it is significant for the planners to understand the microclimatic impact of their design before it is implemented in the master plan.
This paper tries to demonstrate a set of microclimatic analyses of a hypothetical precinct which deals with several aspects, such as outdoor temperature, greenery impact, urban ventilation, district energy performance, and outdoor thermal comfort. In the past, these studies have been done in such a segregated and isolated manner; where one usually focuses on a particular aspect without acknowledging others. The studied precinct was developed with parametric approach, results in multiple design layouts and forms, where each of them has undergone several microclimatic analyses for benchmarking process.
The first part of this study deals with thermal load performances which comprises district sensible cooling load and external heat gains. Furthermore, the wind aspect has been analysed by using the Velocity Ratio (VR) method, which is defined as the area-averaged wind velocity magnitude extracted at a study level over the wind velocity at top of the urban boundary layer that is not affected by ground roughness and other site features. Meanwhile, the outdoor temperature analysis uses Screening Tool for Estate Environment Evaluation (STEVE) tool. STEVE tool is an empirical model that calculates the maximum, minimum and average air temperature of a point of interest based on a 50m radius in an urban area. Lastly, the analysis on outdoor thermal comfort uses Thermal Sensation Vote (TSV) index to predict and evaluate people’s thermal sensation proposed for tropical condition.
This study shows how the microclimate analyses can be done at the early stages of planning process, where planners/designers could be well informed of the environmental impact from their design. Consequently, this study tries to send a message to designers where they have to balance the design objectives on minimizing the external heat gains and at the same time reducing the heat island impact by enhance the wind outflow and implementing greenery. This approach does not have a fully diagnostic aim, such as providing exact and detail run down of performance values at the district level, but rather a comparative figures which will be useful for benchmarking different design options at the same time.