• International Journal of Technology (IJTech)
  • Vol 12, No 3 (2021)

Assessment of the Water Pond Cooling Effect on Urban Microclimate: A Parametric Study with Numerical Modeling

Assessment of the Water Pond Cooling Effect on Urban Microclimate: A Parametric Study with Numerical Modeling

Title: Assessment of the Water Pond Cooling Effect on Urban Microclimate: A Parametric Study with Numerical Modeling
Nedyomukti Imam Syafii, Masayuki Ichinose, Eiko Kumakura, Steve Kardinal Jusuf, Wong Nyuk Hien, Kohei Chigusa, Yasunobu Ashie

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Cite this article as:
Syafii, N.I., Ichinose, M., Kumakura, E., Jusuf, S.K., Hien, W.N., Chigusa, K., Ashie, Y., 2021. Assessment of the Water Pond Cooling Effect on Urban Microclimate: A Parametric Study with Numerical Modeling. International Journal of Technology. Volume 12(3), pp. 461-471

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Nedyomukti Imam Syafii Department of Architecture and Planning, Fakultas Teknik, Universitas Gadjah Mada, Jl. Grafika No. 2 Kampus UGM, Yogyakarta 55281
Masayuki Ichinose Graduate School of Urban Environmental Sciences, Department of Architecture and Building Engineering, Tokyo Metropolitan University, 1-1 Minami-Osawa, Hachioji-shi, Tokyo, Japan 192-0397
Eiko Kumakura Urban Planning Division, Urban Planning Department, National Institute for Land and Infrastructure Management, 1 Tachihara, Tsukuba City, Ibaraki Prefecture, Japan 305-0802
Steve Kardinal Jusuf Engineering, Singapore Institute of Technology, 10 Dover Drive, Singapore, 138683
Wong Nyuk Hien Department of the Built Environment, School of Design and Environment, National University of Singapore, 4 Architecture Drive, #03-04, Singapore 117566
Kohei Chigusa Shimizu Corporation, 3-5-7 Honmachi, Chuo-ku, Osaka 541-8520, Japan
Yasunobu Ashie Department of Environmental Engineering, Building Research Institute, 1 Tachihara, Tsukuba-shi, Ibaraki-ken 305-0802, Japan
Email to Corresponding Author

Abstract
Assessment of the Water Pond Cooling Effect on Urban Microclimate: A Parametric Study with Numerical Modeling

Effective utilization of urban surface modification and landscaping through appropriate planning and design is becoming increasingly important. In contrast to the large number of studies on urban microclimates, few studies have directly focused on the outdoor thermal environment, in particular those investigating the role of water bodies. To optimize the usage of water bodies and to identify the distinguishing factors that may affect the benefits of cooling, a coupled computational fluid dynamics calculation and surface temperature calculation were used to estimate the cooling influence of water bodies on urban microclimates. The study presented in this paper simulated nine unique cases of a simplified urban neighborhood to evaluate the unique effect of different water pond configurations. In summary, within the urban canyon, the study results highlight the importance of a water body’s configuration and positioning. Relative to prevailing winds, larger water pond surfaces tended to produce a better thermal environment, while equally distributed water ponds seemed to influence a wider area.

Cooling effect; Numerical modeling; Thermal environment; Urban canyon; Water body

Introduction

        Considerable variations in land usage, land cover, and urban surface texture in a city contribute to various urban problems, such as an urban heat island (UHI). UHI, where the urban area is warmer than the rural area, affects a building’s energy consumption as well as the occupant’s thermal comfort, health, and well-being (Brontowiyono et al., 2011; Wibowo and Salleh, 2018; Ibrahim et al., 2018). This generates interest among planners and designers in UHI mitigating strategies. Although still limited, research has beenconducted on a water body’s ability to ameliorate a warm urban microclimate. Generally, these studies have shown that the air temperature is 1–5°C lower near water bodies (e.g., lakes, rivers, wetlands, and ponds) in comparison to adjacent built-up areas, particularly during the day (Jusuf et al., 2009; Völker et al., 2013; Lu et al., 2017; Jin et al., 2017; Syafii et al., 2017a; Cai et al., 2018; Jacobs et al., 2020). However, there is still a lack of design consideration in arranging effective water bodies to improve urban thermal environments. Therefore, further investigation is needed to verify the mitigating capacity of water bodies and to advance the current understanding of the influential factors that may be useful for planners and designers.

        The present research, introduced numerical modeling for a comprehensive parametric study. The numerical model consists of the computational fluid dynamics (CFD) calculation and surface temperature calculation (Ca et al., 1999; Ashie and Kagiya, 2010; Ashie and Kono, 2011). Addressing the need to understand the effects and characteristics of water bodies in urban canyons to derive optimum design solutions and guidelines, the present study aimed to evaluate the thermal benefits of water bodies and to provide a better understanding of the various factors that influence the intensity of beneficial water body cooling, including the interactions among air temperature, humidity, wind flows, and the urban water body’s morphology inside an urban canyon. To achieve these objectives, a parametric study was conducted to evaluate the thermal environment around an actual urban canyon (a simplified representation of an urban neighborhood), which had been affected by the configurations of various water bodies. The generic form provides a useful prognostic tool for studying an urban microclimate within a relatively uniform area. It produces outcomes that are more manageable and easier to interpret than other techniques. Parametric studies have mostly focused on the air temperature change caused by the presence of water bodies in urban canyons and the factors influencing the change. Thus, several methods were used to evaluate the effect. First, a climatic map from the numerical result was used to assess how each case influenced the temperature of the study area of interest. The average temperature changes over the entire study area of interest were also evaluated, providing a rough estimate of how a particular case influenced the whole study area of interest. Lastly, an attempt was made to identify the most influential factor by assessing the cooling occurrence in each case in the study area of interest.

Conclusion

This paper presented the results from a parametric study with a hypothetically urban neighborhood in which the water surface area, spatial configuration, and water temperature were varied. Most of the factors affecting cooling of air temperature (pond sizes, arrangements, and thermal capacity) were considered. Coupled numerical modeling, surface temperature calculation, and CFD calculation were used to obtain a better understanding of the effects of these influential factors and to determine the most effective design consideration for a water body’s application inside the urban canyon, where buildings and other urban elements might influence a pond’s microclimate benefits. Parametric studies using numerical simulation have the advantage of allowing a broad sample of urban surface modifications to be analyzed and compared, thanks to the rapid development of computational technology.

The results show that the air temperature is lower near water bodies than near a hard surface (concrete). The water body's ability to reduce the air temperature can be seen as a positive indicator for achieving enhanced thermal environments. Furthermore, the cooling effect of water bodies in urban canyons is influenced by, and depends on, the size and distribution of the water bodies with respect to wind speed and direction. Generally, with the same water surface area, the cases with EQD configurations were able to influence a much larger area of the canyon while the cases with centered configurations tended to generate a greater amount of cool air. Additionally, by keeping the water temperature low, the cooling intensity from the ponds increased significantly. The greatest effect from the chilled water pond occurred in the larger bodies of water.

        However, the current study is limited to a simplified urban residential microclimate. Due to the complexity of the urban structure, surface materials, and other factors, the study’s conclusion may not be appropriate for higher-density urban city spaces. Thus, potential future research on the cooling impact of water bodies could include factors, such as the influence of other types of water bodies (e.g., flowing water, water spray, water wall, etc.) in combination with other surface modifications (e.g., trees, shading devices, etc.), a more detailed water bodies form factor, or even exposure to a different predominant microclimate. Furthermore, the current study demonstrates the possibility of enhancing the cooling benefits of water bodies by introducing chilled water, which needs further investigation.

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