Optically Modulated Passive Broadband Daytime Radiative Cooling Materials Can Cool Cities in Summer and Heat Cities in Winter

Ansar Khan, Laura Carlosena, Jie Feng, Samiran Khorat, Rupali Khatun, Quang- Van Doan and Mattheos Santamouris
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Ansar Khan: Department of Geography, Lalbaba College, University of Calcutta, Howrah 711202, India
Laura Carlosena: Department of Engineering, Arrosadia Campus, Public University of Navarra (UPNA), 31006 Pamplona, Spain
Jie Feng: Faculty of Built Environment, University of New South Wales, Sydney, NSW 2052, Australia
Samiran Khorat: Department of Geography, University of Calcutta, Kolkata 700019, India
Rupali Khatun: School of Environmental Studies, Jadavpur University, Kolkata 700032, India
Quang- Van Doan: Centre for Computational Sciences, University of Tsukuba, Tsukuba 305 8577, Ibaraki, Japan
Mattheos Santamouris: Faculty of Built Environment, University of New South Wales, Sydney, NSW 2052, Australia

Sustainability, 2022, vol. 14, issue 3, 1-18

Abstract: Broadband passive daytime radiative cooling (PDRC) materials exhibit sub-ambient surface temperatures and contribute highly to mitigating extreme urban heat during the warm period. However, their application may cause undesired overcooling problems in winter. This study aims to assess, on a city scale, different solutions to overcome the winter overcooling penalty derived from using PDRC materials. Furthermore, a mesoscale urban modeling system assesses the potential of the optical modulation of reflectance (ρ) and emissivity (ε) to reduce, minimize, or reverse the overcooling penalty. The alteration of heat flux components, air temperature modification, ground and roof surface temperature, and the urban canopy temperature are assessed. The maximum decrease of the winter ambient temperature using standard PDRC materials is 1.1 °C and 0.8 °C for daytime and nighttime, respectively, while the ρ+ε-modulation can increase the ambient temperature up to 0.4 °C and 1.4 °C, respectively, compared to the use of conventional materials. Compared with the control case, the maximum decrease of net radiation inflow occurred at the peak hour, reducing by 192.7 Wm −2 for the PDRC materials, 5.4 Wm −2 for ρ-modulated PDRC materials, and 173.7 Wm −2 for ε-PDRC materials; nevertheless, the ρ+ε-modulated PDRC materials increased the maximum net radiation inflow by 51.5 Wm −2 , leading to heating of the cities during the winter.

Keywords: urban heat mitigation; broadband radiative cooling emitters; overcooling; optical modulation; WRF-SLUCM; Kolkata (search for similar items in EconPapers)
JEL-codes: O13 Q Q0 Q2 Q3 Q5 Q56 (search for similar items in EconPapers)
Date: 2022
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