considerations of urban design and microclimate in ...weather.cityu.edu.hk/see/ws-sustain/esther...

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

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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

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Study Area – Central, Hong Kong

Conserving Central Scheme (The HK Government’s

Policy 2009-10)

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Study Site – Central Police Station Compound

- Clusters of 18 historic buildings, - 3 Declared monuments in 1995, - Revitalized to a cultural and heritage hub

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Methodology of the analysis

Historical buildings Simulate and improve the thermal comfort of historical buildings

Surrounding buildings Change configurations of surrounding buildings to improve historic buildings site thermal comfort

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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

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Methodology Process Diagram – CFD simulation

3D GIS Data Get detail building geometry data from GIS 3D model

Prepare models for CFD simulation Extract and simplify the 3D model for simulation (Rhino software)

Outdoor Wind environment Get outdoor wind data for wind field simulation

Solar radiation data All year sun path data for Temperature simulation

CFD (Computational Fluid Dynamics) simulation analysis Base on 3d model and climatic data CFD simulation for thermal comfort analysis

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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

Summary of simulation tasks

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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

Site measurement wind velocity data

Validation by field measurements

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CFD Simulation and analysis - Wind velocity

Existing buildings The simulation baseline model

increase surrounding building height The surrounding buildings height is 70m

Compare

Historical building area Wind velocity increase to near 1.2m/s

Surrounding building area Wind velocity decrease to near 0.4m/s Poor air ventilation will result in poor heat dissipation and air pollution

Historical building area Wind velocity near 0.7m/s

Surrounding building area Wind velocity near 2.0m/s

1.5m height data above ground

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CFD Simulation and analysis - Wind velocity

Surrounding building height equal to the tallest historical building The surrounding buildings height is 37m

Compare

Historical building area Wind velocity decrease to near 0.5m/s

Surrounding building area Wind velocity decrease to near 1.0m/s Lower building height not always effectively enhance the air ventilation in dense city

Surrounding building area Wind velocity near 2.0m/s

Historical building area Wind velocity near 0.7m/s

1.5m height data above ground

Existing buildings The simulation baseline model

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Simulation and analysis - Wind velocity

Surrounding building set back (Double width of existing road on prevailing wind direction)

Compare

Historical building area Wind velocity increase to near 1.1m/s

Surrounding building area Wind velocity near 2.0m/s

Historical building area Wind velocity near 0.7m/s

Surrounding building area Wind velocity decrease to near 1.4m/s

1.5m height data above ground

Existing buildings The simulation baseline model

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Simulation and analysis - Wind velocity

Plant grass land of historical building center

Compare

Surrounding building area Wind velocity near 2.0m/s

Historical building area Wind velocity near 0.7m/s

The same as baseline model result

The same as baseline model result

1.5m height data above ground Existing buildings The simulation baseline model

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Simulation and analysis / Wind velocity

Compare

Surrounding building area Wind velocity near 2.0m/s

Historical building area Wind velocity near 0.7m/s

1.5m height data above ground Existing buildings The simulation baseline model

Plant trees on historical building center

greenery area: 66% greenery area: 62%

Historical building area Wind velocity increase to near 0.9m/s

Surrounding building area Wind velocity decrease to near 1.6m/s 16

Simulation and analysis - Air temperature

Increase surrounding building height The surrounding buildings height is 70m

Compare

Surrounding building area Air temperature increase 3.0℃ Poor building air ventilation Cause temperature rising higher

Surrounding building area Air temperature near 33.3℃

Historical building area Air temperature near 36℃

Historical building area Air temperature decrease 2℃ Some part increase over 4℃

1.5m height data above ground

Existing buildings The simulation baseline model

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Simulation and analysis - Air temperature

Surrounding building height equal to historical building The surrounding buildings height is 37m

Compare

Historical building area Air temperature decrease 1.6℃

Surrounding building area Air temperature increase 0.7℃ Poor building air ventilation Cause temperature rising higher

1.5m height data above ground

Surrounding building area Air temperature near 33.3℃

Historical building area Air temperature near 36℃

Existing buildings The simulation baseline model

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Simulation and analysis - Air temperature

Compare

Historical building area Air temperature decrease 2.0℃

Surrounding building area Air temperature increase 1.2℃ Poor building air ventilation Cause temperature rising higher

Surrounding building set back (Double width of existing road on prevailing wind direction)

1.5m height data above ground

Surrounding building area Air temperature near 33.3℃

Historical building area Air temperature near 36℃

Existing buildings The simulation baseline model

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Simulation and analysis / Air temperature

Compare

1.5m height data above ground wall

Surrounding building area Air temperature near 33.3℃

Historical building area Air temperature near 36℃

Existing buildings The simulation baseline model

Wind corridor for enhance ventilation

Historical building area Air temperature decrease 1.3℃

Wind corridor

Surrounding building area Air temperature decrease 0.2℃

Prevailing wind direction in summer

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Simulation and analysis - Air temperature

Compare

Historical building area Air temperature decrease 1.5~2.0℃, tree shadow can mitigate the air temperature at courtyard

Plant trees on historical building center

1.5m height data above ground

Surrounding building area Air temperature near 33.3℃

Historical building area Air temperature near 36℃

The same as baseline model result

Existing buildings The simulation baseline model

greenery area: 66% greenery area: 62%

4m

2m

R=3m

Tree model 21

Simulation and analysis - Air temperature

Compare

Historical building area Air temperature decrease 0.2℃,grass land cannot significantly mitigate the air temperature at courtyard

Plant grass land of historical building center

1.5m height data above ground

Surrounding building area Air temperature near 33.3℃

Historical building area Air temperature near 36℃

The same as baseline model result

Existing buildings The simulation baseline model

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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

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√ 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℃

Summary of simulation tasks HBA: historical building area SBA: surrounding building area

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

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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.

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Construct 3D Model

Drawing 3D building models by software： AutoCAD/Rhino/Revit Use Rhino in this project

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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

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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

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Post Processing

Present simulation result by CFD Post software:

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