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Highly Solar-Reflective Structures for Daytime Radiative Cooling under High Humidity.
Hongmei Zhong1,2, Peng Zhang2, Yanan Li1
1Department of Mechanical Engineering, City University of Hong Kong, Kowloon, Hong Kong 999077, China.
ACS Applied Materials & Interfaces
|November 5, 2020
Summary
This study demonstrates efficient daytime radiative cooling in humid Hong Kong. A novel ePTFE and silver film design achieves 98% solar reflectivity, enabling significant cooling even with high atmospheric water vapor.
Area of Science:
- Materials Science
- Thermal Engineering
- Sustainable Technologies
Background:
- Daytime radiative cooling passively cools objects by reflecting sunlight and emitting heat to space.
- Previous research focused on dry regions, limiting applicability in humid climates.
- High atmospheric water vapor obstructs infrared radiation, challenging radiative cooling in humid areas.
Purpose of the Study:
- To investigate the feasibility of efficient daytime radiative cooling in humid subtropical regions like Hong Kong.
- To develop a practical radiative cooling solution for environments with high atmospheric water vapor.
- To overcome the limitations imposed by the atmospheric transparent window closure due to water absorption.
Main Methods:
- Designed a radiative cooling system using an expanded polytetrafluoroethylene (ePTFE) film and a silver (Ag) layer on glass.
- Evaluated the system's performance under direct sunlight in Hong Kong's humid climate.
- Measured solar reflectivity and temperature drop under simulated solar intensity.
Main Results:
- Achieved 98% reflectivity across the solar spectrum.
- Demonstrated a temperature drop of up to 2.7 °C under 1000 W/m² solar intensity.
- Confirmed the effectiveness of the ePTFE and Ag combination in humid conditions.
Conclusions:
- The developed ePTFE and Ag radiative cooling system is effective in humid subtropical climates.
- This approach offers a viable passive cooling strategy for regions with high atmospheric water vapor.
- The findings contribute to advancing radiative cooling technologies for diverse environmental conditions.
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