Considerations of Urban Design and Microclimate in Historical Buildings Environment under Climate Change Research team: Dr. Esther H.K. Yung, Mr. Z.N. Tan, Dr. C.K. Chau, Prof. Edwin, H.W. Chan Department of Building and Real Estate & Department of Building Service Engineering
Theoretical Background Urban Conservation conservation on an urban scale should concern with the urban fabric as a whole and not with architecture alone. successful conservation of a historic area is the integration of the old and the new in a controlled manner (Cohen, 1999) Department of Building and Real Estate The Hong Kong Polytechnic University 2
Background Effect of climate change - physical impact - social impact Urban heat island effect affects the visitors use of heritage space (Coombes E.G., Jones A.P., 2010; Pang et al., 2013; Brimblecombe, 2015; Yung & Chan, 2015) - what they might do when they are in the space? How to improve micro-climate to enhance people thermal comfort? 3
The Context of Hong Kong Advocate the point-line-plane conservation approach in Hong Kong - design buildings and their surroundings in a sustainable way, Urban design Guidelines Conservation of Heritage Buildings/ Local Characters - Building height step down 4
Aim of the study To incorporate the concept of urban design and thermal comfort into urban conservation - Environmental Comfort (wind ventilation, air temperature, Green area, shadow, air pollutants) - Urban Form (building setback, building height, building mass, views) To formulate urban design guidelines for future redevelopment of the surrounding area of historic building sites Department of Building and Real Estate The Hong Kong Polytechnic University 5
Study Area Central, Hong Kong c Conserving Central Scheme (The HK Government s Policy 2009-10) 6
Study Site Central Police Station Compound - Clusters of 18 historic buildings, - 3 Declared monuments in 1995, - Revitalized to a cultural and heritage hub 7
Methodology of the analysis Surrounding buildings Change configurations of surrounding buildings to improve historic buildings site thermal comfort H Historical buildings Simulate and improve the thermal comfort of historical buildings H Reference research: [ Technical Guide for Air Ventilation Assessment for Developments in Hong Kong. HK Planning Department ] [ AIJ guidelines for practical applications of CFD to pedestrian wind environment around buildings. Yoshihide et al. (AIJ: Architectural Institute of Japan.) Journal of Wind Engineering and Industrial Aerodynamic 96(2008) 1749-1761. ] Software:Ansys Fluent 14.0 version Department of Building and Real Estate The Hong Kong Polytechnic University 8
Methodology Process Diagram CFD simulation 3D GIS Data Get detail building geometry data from GIS 3D model Outdoor Wind environment Get outdoor wind data for wind field simulation Solar radiation data All year sun path data for Temperature simulation Prepare models for CFD simulation Extract and simplify the 3D model for simulation (Rhino software) CFD (Computational Fluid Dynamics) simulation analysis Base on 3d model and climatic data CFD simulation for thermal comfort analysis 9
Summary of simulation tasks Existing Height (baseline model) Height of Surrounding buildings Set back Surrounding buildings Addition of Green area (within the historic building site) Modification of spatial layout surrounding buildings (change to average of the surrounding buildings, 70m) (same as height of the highest historic building on the site, 37m) (double the width of existing road) Grass land Trees (2m) Green roof (grass) Ventilation/wind corridor Wind velocity ) (at 1.5m above ground, m/s) Air temp. (at 1.5m above ground) shadow Pollutants Department of Building and Real Estate The Hong Kong Polytechnic University 10
Validation by field measurements Site measurement wind velocity data Date Time Velocity [m/s] Velocity Min. [m/s] Velocity Max. [m/s] 4/24/2017 3:58:51 PM 1.38 0.24 2.98 4/24/2017 3:59:21 PM 1.58 0.97 2.18 4/24/2017 3:59:51 PM 0.89 0.17 1.85 4/24/2017 4:00:22 PM 1.25 0.08 2.13 4/24/2017 4:00:52 PM 1.03 0.27 1.75 4/24/2017 4:01:23 PM 0.93 0.32 1.66 4/24/2017 4:01:53 PM 0.87 0.45 1.35 4/24/2017 4:02:23 PM 1.12 0.40 2.16 4/24/2017 4:02:54 PM 0.77 0.30 1.58 4/24/2017 4:03:24 PM 0.85 0.07 1.61 avg: 1.1m/s Department of Building and Real Estate The Hong Kong Polytechnic University 11
CFD Simulation and analysis - Wind velocity Compare Existing buildings The simulation baseline model 1.5m height data above ground Wind velocity near 0.7m/s increase surrounding building height The surrounding buildings height is 70m Wind velocity increase to near 1.2m/s Wind velocity near 2.0m/s Wind velocity decrease to near 0.4m/s Poor air ventilation will result in poor heat dissipation and air pollution 12
CFD Simulation and analysis - Wind velocity Compare Existing buildings The simulation baseline model Wind velocity near 0.7m/s 1.5m height data above ground Wind velocity decrease to near 1.0m/s Lower building height not always effectively enhance the air ventilation in dense city Surrounding building height equal to the tallest historical building The surrounding buildings height is 37m Wind velocity decrease to near 0.5m/s Wind velocity near 2.0m/s 13
Simulation and analysis - Wind velocity Compare Existing buildings The simulation baseline model 1.5m height data above ground Wind velocity near 0.7m/s Surrounding building set back (Double width of existing road on prevailing wind direction) Wind velocity increase to near 1.1m/s Wind velocity decrease to near 1.4m/s Wind velocity near 2.0m/s 14
Simulation and analysis - Wind velocity Compare Existing buildings The simulation baseline model 1.5m height data above ground Plant grass land of historical building center Wind velocity near 0.7m/s The same as baseline model result Wind velocity near 2.0m/s The same as baseline model result 15
Simulation and analysis / Wind velocity Compare Existing buildings The simulation baseline model 1.5m height data above ground Wind velocity near 0.7m/s Plant trees on historical building center Wind velocity increase to near 0.9m/s greenery area: 66% greenery area: 62% Wind velocity near 2.0m/s Wind velocity decrease to near 1.6m/s 16
Simulation and analysis - Air temperature Compare 1.5m height data above ground Existing buildings The simulation baseline model Air temperature near 36 Increase surrounding building height The surrounding buildings height is 70m Air temperature decrease 2 Some part increase over 4 Air temperature increase 3.0 Poor building air ventilation Cause temperature rising higher Air temperature near 33.3 17
Simulation and analysis - Air temperature Compare Existing buildings The simulation baseline model 1.5m height data above ground Air temperature near 36 Surrounding building height equal to historical building The surrounding buildings height is 37m Air temperature decrease 1.6 Air temperature near 33.3 Air temperature increase 0.7 Poor building air ventilation Cause temperature rising higher 18
Simulation and analysis - Air temperature Compare 1.5m height data above ground Existing buildings The simulation baseline model Air temperature near 36 Surrounding building set back (Double width of existing road on prevailing wind direction) Air temperature decrease 2.0 Air temperature near 33.3 Air temperature increase 1.2 Poor building air ventilation Cause temperature rising higher 19
Simulation and analysis / Air temperature Compare 1.5m height data above ground wall Existing buildings The simulation baseline model Air temperature near 36 Wind corridor for enhance ventilation Air temperature decrease 1.3 Wind corridor Air temperature near 33.3 Air temperature decrease 0.2 Prevailing wind direction in summer 20
Simulation and analysis - Air temperature Compare 1.5m height data above ground Existing buildings The simulation baseline model Air temperature near 36 R=3m Plant trees on historical building center Air temperature decrease 1.5~2.0, tree shadow can mitigate the air temperature at courtyard 2m 4m greenery area: 66% greenery area: 62% Air temperature near 33.3 Tree model The same as baseline model result 21
Simulation and analysis - Air temperature Compare Existing buildings The simulation baseline model 1.5m height data above ground Air temperature near 36 Plant grass land of historical building center Air temperature decrease 0.2,grass land cannot significantly mitigate the air temperature at courtyard The same as baseline model result Air temperature near 33.3 22
Summary of simulation tasks HBA: historical building area SBA: surrounding building area Existing Height (baseline model) Height of Surrounding buildings Set back Surrounding buildings Addition of Green area (within the historic building site) Modification of spatial layout surrounding buildings (change to average of the surrounding buildings, 70m) (same as height of the highest historic building on the site, 37m) (double the width of existing road) Grass land Trees (2m) Green roof (grass) ventilation corridor Wind velocity (at 1.5m above ground, m/s) HBA: near 0.7m/s SBA: near 2.0m/s HBA: near 1.2m/s SBA: near 0.4m/s HBA: near 0.5m/s SBA: near 1.0m/s HBA: near 1.1m/s SBA: near 1.4m/s HBA: near 0.7m/s SBA: near 2.0m/s HBA: near 0.9m/s SBA: near 1.6m/s HBA: near 0.8m/s SBA: near 2.0m/s Air temp. (at 1.5m above ground) HBA: near 36 SBA: near 33.3 HBA: near 34 SBA: near 36.3 HBA: near 34.4 SBA: near 34 HBA: near 34 SBA: near 34.8 HBA: near 35.8 SBA: near 33.3 HBA: near 34~34.5 SBA: near 33.3 HBA: near 34.7 SBA: near 33.1 Department of Building and Real Estate The Hong Kong Polytechnic University 23
preliminary findings and suggestions 1. Building Height Surrounding buildings of different height provide better wind ventilation and thermal comfort temperature than equal height in an urban dense city. 2. Building Set Back can improve wind ventilation in some areas (but not enhance all areas in dense city. 3. Tree Shadowing can improve the historical building area s thermal comfort with lower air temperature. 4. Wind corridor can improve high dense city s air ventilation and thus lower the air temperature. Dense city has complex architectural morphology which affects thermal comfort,more investigations on different design and spatial planning parameters and their implication to human behavior should be done for built heritage sites in the future. e.g. conservation management plan should provide more detailed guidelines on the design of the surrounding built environment. Department of Building and Real Estate The Hong Kong Polytechnic University 24
Thank you esther.yung@polyu.edu.hk Department of Building and Real Estate The Hong Kong Polytechnic University 25
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CFD simulation process Ansys Fluent 28
Computational Fluid Dynamics CFD is a branch of fluid mechanics using numerical methods and algorithms to solve and analyze problems that involve fluid flows. Computers are used to perform the millions of calculations required to simulate the interaction of fluids and gases with the complex surfaces used in engineering. 29
Construct 3D Model Drawing 3D building models by software: AutoCAD/Rhino/Revit Use Rhino in this project 30
Mesh generation 3D un-structure mesh is generated by ICEM software: Detail and enough mesh quantity to keep accuracy Keep four or more mesh layers to improve mesh quality and to get detail simulation result for estimate 31
Fluent solver setting Define boundary condition and Setting boundary conditions for the simulation domain Until simulation iteration come to residual converge standard, the result is acceptable 32
Post Processing Present simulation result by CFD Post software: 33