Developing Urban Heat Mitigation Strategies for a Historic Area Using a High-Fidelity Parametric Numerical Simulation: A Case Study in Singapore
Abstract
:1. Introduction
2. Methodology
2.1. Simulation Scenarios Description
2.2. CFD Simulation Setup
2.2.1. Computational Domain and Meshing
2.2.2. Boundary Conditions
2.3. Data Analysis
3. Results and Analysis
3.1. Comparison of Wind Speed between Cases A and B
3.2. Comparison of Air Temperature Increments among Cases C, D, and E
3.3. Urban Heat Mitigation Strategies Evaluation among Case F, G, and H
4. Discussion
4.1. Effect of Anthropogenic Heat and Urban Morphology on the Urban Heat Environment in the Singapore Chinatown Area
4.2. Practical Implications for Proposed Mitigation Strategies in Historic Areas
5. Conclusions
- The average wind speed decreases of 43%, from 1.11 m/s in Case A to 0.63 m/s in Case B. This indicates the great impact of new development, i.e., high-rise buildings, on pedestrian-level air flow of the historic area.
- The mean air temperature increased by 0.16 °C for Case C, 0.52 °C for Case D and 0.87 °C for Case E, respectively. This indicates that the anthropogenic heat emission from surrounding high-rise buildings had less effect than that from historic shophouses in Chinatown.
- The integration of open spaces and building porosity, which create wind corridors together, can promote outdoor natural ventilation and heat dispersion at the study area. Compared with Case E, the three mitigation cases improve outdoor thermal environment, with mean temperature reduction of 33%, 25%, and 21%, respectively.
- To retain the urban texture of the area, the locations and number of removed shophouses should include either one shophouse closer to the wind inlet and perpendicular to the wind direction as a priority, or a number of shophouses at the end or in the middle of the row where heat emission accumulates, in some cases.
6. Limitations and Future works
Author Contributions
Funding
Data Availability Statement
Acknowledgments
Conflicts of Interest
Nomenclature
Abbreviations | |
ABL | Atmospheric boundary layer |
AC | Air-conditioning |
BCA | Building and construction authority |
CBD | Central Business District |
CFD | Computational fluid dynamics |
COP | Coefficient of performance |
NE | Northeast |
NEA | National environment agency |
UHI | Urban heat island |
Symbols | |
Gross floor area of buildings (m2) | |
Typical area of one unit of residential buildings (m2) | |
Gross floor area (m2) | |
Specific heat of air (J·kg−1·K−1) | |
Model constant | |
Cooling energy (kw) | |
E2 | Energy Efficient Singapore |
Input mass flow rate of heat emissions (kg·s−2) | |
Number of units in residential buildings | |
Floor number of residential buildings | |
Total anthropogenic heat (kw) | |
Anthropogenic heat from each unit of residential buildings (kw) | |
Cooling loads generated in the indoor spaces (kw) | |
Public area ratio | |
Atmospheric boundary layer friction velocity (m/s) | |
Hight above ground (m) | |
Aerodynamic roughness length (m) | |
Specific dissipation (s−1) | |
Turbulent kinetic energy (m2·s−2) | |
TKE dissipation rate (m2·s−3) |
Appendix A
AC Type | Building Function | Equation |
---|---|---|
Air cooling | Shophouses (retail) | |
Residential buildings | ||
Water cooling | Retail | |
Office | ||
Hotel |
Appendix B
RTL1 | RTL2 | RTL3 | RTL4 | RTL5 | RTL6 | RTL7 | RTL8 | RTL9 | RTL10 | RTL11 | RTL12 | RTL13 | FTL1 | FTL2 | FTL3 | FTL4 | FTL5 | Ave | |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Case A | 0.73 | 1.06 | 1 | 0.96 | 1.07 | 1.8 | 0.79 | 0.46 | 1.01 | 0.96 | 2.23 | 1.51 | 0.94 | 1.67 | 1.67 | 0.62 | 0.58 | 0.93 | 1.11 |
Case B | 1.01 | 0.54 | 0.61 | 0.76 | 0.8 | 0.76 | 0.45 | 0.36 | 0.34 | 0.51 | 0.45 | 0.64 | 1.15 | 0.54 | 0.36 | 0.32 | 1.07 | 0.64 | 0.63 |
Case B-A | 38% | −49% | −39% | −21% | −25% | −58% | −43% | −22% | −66% | −47% | −80% | −58% | 22% | −68% | −78% | −48% | 84% | −31% | −43% |
Case C | 1.39 | 0.92 | 1.7 | 2.26 | 1.75 | 0.69 | 0.47 | 0.52 | 0.84 | 1.92 | 1.16 | 1.16 | 2.34 | 1.21 | 1.13 | 1.94 | 2.23 | 0.9 | 1.36 |
Case D | 1.39 | 1.47 | 0.99 | 1.43 | 1 | 0.91 | 2.82 | 0.57 | 0.88 | 1.1 | 1.08 | 0.69 | 1.57 | 0.43 | 1.36 | 0.81 | 0.96 | 1.51 | 1.17 |
Case E | 1.62 | 1.62 | 1.52 | 2.38 | 1.44 | 1.19 | 0.39 | 0.33 | 1.52 | 1.86 | 1.27 | 1.31 | 3.04 | 1.36 | 1.17 | 0.62 | 2.09 | 2.25 | 1.47 |
Case C-E | −14% | −21% | 12% | −5% | 22% | 42% | 21% | 58% | 45% | 3% | −9% | −12% | −23% | −11% | −3% | 213% | 7% | −60% | −8% |
Case D-E | −14% | 27% | 35% | 40% | −31% | −24% | 623% | 73% | −42% | −41% | −15% | −47% | −48% | −68% | 16% | 31% | −54% | −33% | −21% |
Case F | 1.9 | 1.8 | 2.08 | 2.49 | 1.64 | 1.07 | 0.58 | 0.42 | 1.13 | 1.81 | 2.35 | 2.23 | 2.21 | 2.28 | 1.39 | 0.47 | 2.44 | 0.76 | 1.61 |
Case G | 1.61 | 1.38 | 1.77 | 1.89 | 2.25 | 2.06 | 0.68 | 0.82 | 1.24 | 1.69 | 1.96 | 1.5 | 3.84 | 1.86 | 0.77 | 0.89 | 1.06 | 1.31 | 1.59 |
Case H | 1.22 | 1.62 | 1.16 | 1.62 | 0.79 | 1.98 | 0.77 | 1.18 | 1.23 | 1.46 | 2.32 | 1.88 | 1.74 | 2.39 | 0.97 | 0.79 | 1.26 | 1.29 | 1.43 |
Case F-E | 17% | 55% | 37% | 5% | 14% | −10% | 49% | 27% | −26% | −3% | 85% | 70% | −27% | 68% | 19% | −24% | 17% | −66% | 10% |
Case G-E | −1% | 19% | 16% | −21% | 56% | 73% | 74% | 148% | −18% | −9% | 54% | 15% | 26% | 37% | −34% | 44% | −49% | −42% | 8% |
Case H-E | −25% | 40% | −24% | −32% | −45% | 66% | 97% | 258% | −19% | −22% | 83% | 44% | 43% | 76% | −17% | 27% | −40% | −43% | −3% |
RTL1 | RTL2 | RTL3 | RTL4 | RTL5 | RTL6 | RTL7 | RTL8 | RTL9 | RTL10 | RTL11 | RTL12 | RTL13 | FTL1 | FTL2 | FTL3 | FTL4 | FTL5 | Ave | |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Case C | 0.22 | 0.19 | 0.15 | 0.12 | 0.16 | 0.25 | 0.2 | 0.25 | 0.08 | 0.06 | 0.21 | 0.11 | 0.13 | 0.12 | 0.12 | 0.11 | 0.24 | 0.14 | 0.16 |
Case D | 0.46 | 0.49 | 0.78 | 1.05 | 0.3 | 0.43 | 0.24 | 0.57 | 0.39 | 1.14 | 0.04 | 0.54 | 0.09 | 0.77 | 0.95 | 0.64 | 0.35 | 0.07 | 0.52 |
Case E | 1.3 | 1.26 | 1.42 | 0.92 | 1.16 | 1.03 | 1.43 | 1.08 | 0.37 | 0.31 | 0.48 | 0.67 | 0.13 | 1.45 | 0.94 | 0.89 | 0.49 | 0.35 | 0.87 |
Case C-E | −83% | −85% | −89% | −87% | −86% | −77% | −86% | −77% | −78% | −81% | −56% | −84% | 0 | −92% | −87% | −88% | −51% | −60% | −82% |
Case D-E | −65% | −61% | −45% | 14% | −74% | −58% | −83% | −47% | 5% | 268% | −92% | −19% | −31% | −47% | 1% | −28% | −29% | −80% | −41% |
Case F | 0.71 | 0.32 | 0.97 | 0.95 | 0.78 | 0.73 | 1.18 | 0.62 | 0.51 | 0.51 | 0.28 | 0.28 | 0.23 | 0.23 | 0.59 | 0.89 | 0.26 | 0.46 | 0.58 |
Case G | 1.05 | 0.64 | 1.41 | 1.35 | 0.39 | 0.75 | 0.34 | 0.98 | 0.3 | 0.29 | 0.29 | 0.39 | 0.01 | 0.2 | 1.09 | 1.07 | 0.91 | 0.23 | 0.65 |
Case H | 0.86 | 0.69 | 0.89 | 1.43 | 1.12 | 0.6 | 1.02 | 0.68 | 0.46 | 0.69 | 0.22 | 0.37 | 0.88 | 0.23 | 0.42 | 0.9 | 0.69 | 0.2 | 0.69 |
Case F-E | −45% | −75% | −32% | 3% | −33% | −29% | −18% | −43% | 38% | 65% | −42% | −58% | 77% | −84% | −37% | 0 | −47% | 31% | −33% |
Case G-E | −19% | −49% | −1% | 47% | −66% | −27% | −76% | −9% | −19% | −6% | −40% | −42% | −92% | −86% | 16% | 20% | 86% | −34% | −25% |
Case H-E | −34% | −45% | −37% | 55% | −3% | −42% | −29% | −37% | 24% | 123% | −54% | −45% | 577% | −84% | −55% | 1% | 41% | −43% | −21% |
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Cases | Description | Aim |
---|---|---|
Case A | Represents urban geometry of the study area in 1960s | Step 1: To clarity the impact of new development on pedestrian-level air flow |
Case B | Represents urban geometry of the study area in 2020s | |
Case C | The urban geometry of 2020s and anthropogenic heat from the surrounding high-rise buildings are applied | Step 2: To assess the air temperature increment caused by anthropogenic heat emitted |
Case D | The urban geometry of 2020s and anthropogenic heat from the historic shophouses are applied | |
Case E | The urban geometry of 2020s and anthropogenic heat from both high-rise buildings and the historic shophouses are applied | |
Case F | The mitigation strategy is to create horizontal porosity and open spaces by removing some shophouses | Step 3: To develop the mitigation strategies based on the assessment from previous two steps |
Case G | The mitigation strategy is to create both vertical and horizontal porosity by modifying the geometry of the surrounding high-rise buildings | |
Case H | The mitigation strategies in Case F and G are integrated in this case |
Turbulence Model | SST k-ω |
---|---|
Computational grid type | Unstructured poly-hexcore meshes |
Blockage ratio | <5% |
Grid expansion ratio | 1.2 |
Density | Boussinesq |
Solving algorithms | SIMPLE |
Input wind profile | Power law equation |
Inflow boundary condition | Operating temperature: 27 °C |
Incoming wind speed | Power-law profile with the reference wind speed of 7.6 m/s at 300 m above the ground |
Incoming wind directions | northeast (the prevailing wind direction of Singapore) |
Heat flow specification method | Mass flow rate inlet: normal to boundary direction (Heat emission temperature: 40 °C) |
Other boundary conditions |
Outflow: pressure outlet Bottom and buildings: Wall Top: Symmetry |
Convergence criteria | 1E-6 for all variables |
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Zhu, W.; Zhang, L.; Mei, S.-J.; Yuan, C. Developing Urban Heat Mitigation Strategies for a Historic Area Using a High-Fidelity Parametric Numerical Simulation: A Case Study in Singapore. Buildings 2022, 12, 1311. https://doi.org/10.3390/buildings12091311
Zhu W, Zhang L, Mei S-J, Yuan C. Developing Urban Heat Mitigation Strategies for a Historic Area Using a High-Fidelity Parametric Numerical Simulation: A Case Study in Singapore. Buildings. 2022; 12(9):1311. https://doi.org/10.3390/buildings12091311
Chicago/Turabian StyleZhu, Wei, Liqing Zhang, Shuo-Jun Mei, and Chao Yuan. 2022. "Developing Urban Heat Mitigation Strategies for a Historic Area Using a High-Fidelity Parametric Numerical Simulation: A Case Study in Singapore" Buildings 12, no. 9: 1311. https://doi.org/10.3390/buildings12091311