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| Fig. 1: Skyline of Marina Bay and Financial District of Singapore. (Source: Wikimedia Commons) |
In recent years, there has been rapid urbanization and densification in the tropical climates found in Southeast Asia, with many cities suffering from the environmental and societal challenges presented by the urban heat island effect (UHI). [1] Although present in over 400 major cities, UHI is particularly impactful during heat waves in already hot climates. [1]
Shown in Fig. 1, highly dense centers like Singapore can reach UHI intensities of 5°C. With the projected increase of density from 7841 people/km2 (2016) to 9600 people/km2 (2030), this effect is predicted to increase by an additional 1.4°C. [2]
There are many factors that contribute to UHI, including reduced windspeed from urban roughness, radiation trapping, thermal material properties of surrounding buildings, lack of vegetation and anthropogenic heat from human activity. [2] Included in this anthropogenic heat is the released near-surface waste heat of air conditioning (AC) units very prevalent in tropical cities, which also coincides with almost 37% of total electricity consumption in residential areas in Singapore. [3]
It is important to track the waste heat and energy consumption of ACs to mitigate UHI and meet future energy goals, as the usage of AC climbs year to year. [2] Studies performed on the heat and energy impacts of AC like one performed by Salamanca et al. have shown that setting ac waste heat to 0 can result in decreases of 1°C of night-time temperatures and 1277 MWh of daily energy saving in other metropolitan areas like Phoenix. [4]
However, it is unrealistic to expect complete removal of AC from hot urban centers, so we turn to other cooling methods that either provide internal cooling without excess waste heat, or passive internal cooling without large energy consumption.
Windows comprise the building envelopes of nearly all buildings present in urban centers, and contribute to 75% of the heat loss/gain of buildings, and responsible for up to 60% of the total energy consumption of a building. [5,6] A majority of this energy consumption indirectly appears from heat loss and cooling demands, and poor window design can lead to uneven indoor heating and lighting concerns. [7] By implementing active smart window technologies like thermotropic, electrochromic and photochromic windows, you can control the heat and light emissions to optimize energy efficiency and reduce the need for AC. [7] If the implementation of these dynamic windows allowed for the lowering of AC usage in Singapore, we could see near-surface temperature decreases of up to 1.5°C. [2]
Considering the rapid urbanization and climate change in our world, UHI has increasingly significant risk to health and extreme temperatures in cities. If insufficiently explored, mitigation strategies will not be implemented in time for particularly at-risk cities in tropical and subtropical climates to avoid record temperatures and dangerous effects.
© Charm Feng Ang. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] A. Aflaki et al., "Urban Heat Island Mitigation Strategies: A State-of-the-Art Review on Kuala Lumpur, Singapore and Hong Kong," Cities 62, 131 (2017).
[2] M. D. Mughal, X.-X Li, and L. K. Norford, "Urban Heat Island Mitigation in Singapore: Evaluation Using WRF/Multilayer Urban Canopy Model and Local Climate Zones," Urban Clim. 34, 100714 (2020).
[3] K. J. Chua et al., "Achieving Better Energy-Efficient Air Conditioning - A Review of Technologies and Strategies," Appl. Energy 104, 87 (2013).
[4] F. Salamanca et al., "Anthropogenic Heating of the Urban Eenvironment Due to Air Conditioning," J. Geophys. Res.: Atmos. 119, 5949 (2014).
[5] Y. Sun, R. Wilson, and Y.Wu, "A Review of Transparent Insulation Material (TIM) For Building Energy Saving and Daylight Comfort," Appl. Energy 226, 713 (2018).
[6] J. Lee et al., Optimization of Building Window System in Asian Regions by Analyzing Solar Heat Gain and Daylighting Elements," Renew. Energy 50, 522 (2013).
[7] J. Zhao amd Y. Du, "Multi-Objective Optimization Design For Windows and Shading Configuration Considering Energy Consumption and Thermal Comfort: A Case Study For Office Building in Different Climatic Regions of China," Sol. Energy 206, 997 (2020).
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