Impact of Green Roof on Urban Canopy Layer
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IMPACT OF GREEN ROOF ON URBAN CANOPY LAYER MICROCLIMATES IN PLANNED RESIDENTIAL AREA OF DHAKA, BANGLADESH by Ruksana Afroz Thesis submitted in partial fulfillment of the requirement for the degree of MASTERS OF ARCHITECTURE December 2016 Department of Architecture BANGLADESH UNIVERSITY OF ENGINEERING AND TECHNOLOGY Dhaka, Bangladesh ii iii iv DEDICATION To my son and my parents. Arham Araf Md. Hafizur Rahman Dilara Rahman v ACKNOWLEDGEMENTS It is a pleasure to acknowledge my gratitude and gratefulness to my supervisor Dr. Khandaker Shabbir Ahmed, Professor and Head, Department of Architecture, Bangladesh University of Engineering and Technology (BUET) for his constructive advice, guidance and for his support, which was always forthcoming in many difficult moments. My thanks to my honorable teachers at Bangladesh University of Engineering and Technology, for providing a stimulating academic environment, inspiration and guidance. I am grateful to my friend Samina Mazumder Tuli, Lecturer, Department of Architecture, Bangladesh University of Engineering and Technology (BUET) for her warmth and support regarding software and other technical details. I thank Ar. Khondoker Tariqul Islam, Sr. Lecturer, Department of Architecture, Bangladesh University, Mr. Irfan Ahmed Khan and Farzana Jahan for their support. I would like to acknowledge my dear students Habil Uddin, Zakiul Islam, Salauddin Ahmed and Mustafa Tarique Hadi for their help in the field works. I am grateful to my colleague and office staffs for granting me to study and share my work load during my study period. Finally, I wish to thank my family, especially my parents for their encouragement and support. Highest support came from my son who allowed me to work hours after hours uninterruptedly even at his play time with me. vi Abstract: Dhaka is a fast growing city in Asia. To accommodate the population of this city, Dhaka has been growing both horizontally and vertically. As a result, much needed green spaces are being replaced by built-up areas at an unprecedented pace and leading to Urban Heat Island (UHI) effect. As the UHI effect is caused mainly due to widespread use of synthetic materials like asphalt and concrete, it results in increased heat storage capacity and reduction of evapotranspiration. As a result, the outdoor temperature of densely built-up areas in Dhaka is higher than the immediate urban zones, and the average meteorological record. Urban Heat Island effect stresses both electricity supply and quality of urban life. A proven way to balance the thermal budget and quality of life in buildings or cities is by improving the building envelope as well as the cityscape. In this shortfall of urban land and continuous pressure of urbanization, green roofs can be a potential remedy to this problem. Previous studies have identified green-roofs’ benefits in cooling off and energy-conservation in urban multi-storied buildings. However, limited exploration had been done to its wider influence on urban canopy layer microclimate. This study is concerned with the microclimatic aspects within urban canopy layers, and the impact of the green roof on planned residential areas. This study is multidisciplinary in character. Overall, it is an experimental research, which includes a combination of experimental method and simulation method. Field investigation was conducted to find out the existing condition of microclimate at Urban Canopy Layer (UCL) for selected sites. To identify the impact of the green roof on UCL, simulation studies were done. The result of this study will help us understand the status of the present microclimate of planned residential areas in a tropical city, Dhaka. It will shed light on the thermal impact of the green roof on microclimate within the UCL. Additionally, this study will yield directions for developing possible strategies for using green-roof in tropical urban contexts based on findings relating to the possible influence of green roof on near ground environment. The findings would highlight the potentials of green-roof as a retrofitted solution or as a new installation for cooling, mitigation of urban heat island effect and for providing a more desirable outdoor environment for urban residents. vii Table of content Acknowledgements v Abstract vi Table of contents vii List of figures x List of tables xiii List of Abbreviations xiv Chapter One: Preamble 1.1 Background 02 1.2 Statement of the Problem 03 1.3 Aim and Objectives of the Study 06 1.4 Methodology 07 1.4.1 Literature Survey 09 1.4.2 Field Survey 09 1.4.3 Parametric Study 12 1.4.4 Analysis and Synthesis 13 1.5 Research Strategy 14 1.6 Research Quality Consideration 15 1.7 Scope and Limitations 15 1.8 References 16 Chapter Two: Urban Context, Climate and Green Roof 2.1 Introduction 22 2.2 The Context 22 2.2.1 Climatic Context of Dhaka 22 2.2.2 Planned Residential Areas of Dhaka 26 2.2.3 Growth Pattern, Urban Morphology and Population of Dhaka 27 viii 2.2.4 Ratio of Built Space to Open Space 29 2.2.5 Roof: Present Condition of Dhaka City 29 2.3 Urban Canopy Layer (UCL) 30 2.4 Microclimate 32 2.5 Green Roof 34 2.5.1 Typology of Green Roof 34 2.5.2 History of Green Roof 35 2.5.3. Advantages of Green Roof 36 2.5.4. Green Roof as Sustainable Design Tool 36 2.5.5. Limitations of Green Roof 38 2.6. Environmental Issues that Influence Thermal Environment for Tropical City 38 2.6.1. Urban Heat Island Effect Mitigation 38 2.6.2. Effect of Temperature on Energy Consumption for Urban Area 40 2.6.3. Healthy City Concept in Reference to Dhaka 41 2.7. Simulation Software 42 2.8 Conclusion 44 2.9 References 45 Chapter Three: Field Survey and Simulations Study 3.1 Introduction 55 3.2 Methodology 55 3.3 Field Survey 56 3.3.1 Selection Criteria of Study Area 56 3.3.2 Morphology of the Selected Area 58 3.3.3 Data Collection Strategy 62 3.3.4 Data Collection Points 63 3.3.5 Data Collection Time 65 3.3.6. Instrumentation 66 ix 3.4 Simulation Tool: ENVI-met 66 3.5 Comparative study: Data from Field Survey and Data from Simulation for Existing Field Conditions 72 3.6 Conclusion 72 3.7 References 73 Chapter Four: Analysis of Results and Findings 4.1 Introduction 75 4.2 Field Data Analysis and Findings 75 4.2.1 Study Area One (Uttara) 75 4.2.2 Study Area Two (Basundhara) 77 4.2.3 Field Data Comparison Between Two Study Areas 80 4.3 Simulation Data Analysis and Findings 82 4.3.1 Study Area One (Uttara) 82 4.3.2 Study Area Two (Basundhara) 90 4.4 Discussion 98 4.5 Conclusion 99 Bibliography 101 Appendix: Appendix 1: Field Data 113 Appendix 2: Data from Simulation Studies 117 Appendix 3: Simulation Output 129 Appendix 4: Results of Paired Sample T-Test 189 Appendix 5: Instrumentation 191 x List of figures Page Figure No. Title of the figure No. Geographical position of Bangladesh in the world context and position Figure 1.4.2 10 of Dhaka in Bangladesh. Figure 1.4.4 Flowchart of Analysis of the study. 13 Climate Classification of Bangladesh, derived from World Koppen Figure 2.2.1.a 22 Classification Figure 2.2.1.b Average Weather Condition of Dhaka (BBC weather) 24 Monthly Average Dry Bulb Temperature (a) and Monthly Average Figure 2.2.1.c Relative Humidity of Dhaka city from the year 2008-2015. Derived from 24 the data of Meteorological Department of Bangladesh. Annual Mean Temperature of Dhaka, Tangail and Mymensingh city Figure 2.2.1.d from the year 1985-2015. Derived from the data of Meteorological 25 Department of Bangladesh. Mean Temperature of the month of April of Dhaka, Tangail and Figure 2.2.1.e Mymensingh city from the year 1985-2015. Derived from the data of 25 Meteorological Department of Bangladesh. Schematic of climatic scales and vertical layers found in urban areas. Figure 2.3.a PBL – planetary boundary layer, UBL – urban boundary layer, UCL – 31 urban canopy layer [modified from Oke, 1997] Figure 2.3.b Schematic of Urban Canopy Layer (local scale and micro scale) 31 Section of Extensive Green Roof (left) and Photo of Extensive Green Figure 2.5.1.a 34 Roof. Section of Intensive Green Roof (left and below) and Photo of Intensive Figure 2.5.1.b 35 Green Roof. The trend of green space declination in Dhaka city (Tabassum and Figure 2.6.3 41 Sharmin, 2011) Location of planned residential areas in Dhaka and position of selected Figure 3.3.1 57 study area one (Uttara) and study area two (Basundhara). Satellite image of Study area One; Uttara. (Retrieved from: Figure 3.3.2.a www.googlemap.com, 15-02-2016) [Left one]. Photographs of Study 58 area one; Uttara (Date of Photo Taken 26-04-2016) [Right one] Figure 3.3.2.b Plan of study area one; Uttara and ENVI-met model 59 Figure 3.3.2.c East-West elongated Section of study area one; Uttara 60 xi Figure No. Title of the figure Page No. Satellite image of Study area Two; Bashundhara. (Retrieved from: Figure 3.3.2.d www.googlemap.com, 15-02-2016) [Left one]. Photographs of Study 60 area one; Uttara (Date of Photo Taken 26-04-2016) [Right one] Figure 3.3.2.e Plan of study area two; Basundhara and ENVI-met model 61 Figure 3.3.2.f East-West elongated Section of study area two; Basundhara 62 Figure 3.3.3 Radiation Shield for proper ventilation at the time of field measurement 63 Measurement point in section for field data collection for study area Figure 3.3.4.a: 64 one (Uttara) (left) and study area Two (Basundhara)(right).