Design, fabrication, and application of daytime radiative cooling

Zhou, Kai

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https://hdl.handle.net/2142/129715 Copy

Description

Title

Design, fabrication, and application of daytime radiative cooling

Author(s)

Zhou, Kai

Issue Date

2025-04-27

Director of Research (if dissertation) or Advisor (if thesis)

Cai, Lili

Doctoral Committee Chair(s)

Cai, Lili

Committee Member(s)

• Saif, Taher
• Miljkovic, Nenad
• Cropek, Donald M.

Department of Study

Mechanical Sci & Engineering

Discipline

Mechanical Engineering

Degree Granting Institution

University of Illinois Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• radiative cooling
• material design
• radiative cooling composite

Abstract

Passive daytime radiative cooling (PDRC) offers a sustainable strategy to combat global warming by cooling surfaces below ambient temperatures without energy consumption. This technology leverages materials with high solar reflectance and infrared emissivity to dissipate heat into space. However, the widespread adoption of PDRC has been limited by challenges such as costly fabrication, complex manufacturing processes, and susceptibility to environmental contamination. This dissertation addresses these barriers through innovative material designs, scalable fabrication methods, and practical system integration for real-world applications. The first study introduces a rapidly fabricated nanoporous polymer composite produced using commercial molding techniques. The material achieves a high solar reflectance of 96.2% and infrared emissivity of >90%, demonstrating a sub-ambient temperature reduction of 6.1°C and a cooling power of 85 W/m² under direct sunlight. This cooling composite offers a low-cost solution for material design and fabrication in the radiative cooling field. Building on this, the second study further develops a hierarchically structured nanoporous composite with integrated self-cleaning properties. The improved template molding method creates the patterned surface at low cost while achieving a superhydrophobicity-based self-cleaning function. Thermal tests and wettability experiments demonstrate exceptional cooling performance and resistance to environmental liquid and solid contaminants. This multifunctional design utilizes a one-step fabrication technique enabling maintenance-free operation of radiative cooling in outdoor environments. The third study advances fabrication flexibility through an additive manufacturing approach, creating customizable 2D/3D structures using polymer-nanoparticle inks. The ink components were optimized through scattering-based simulation, rheological measurements, and optical property characterization. The optimal recipe demonstrates good compatibility with the additive manufacturing technique, as well as excellent outdoor cooling performance in temperature reduction (7.4 °C) and cooling power (104 W/m2). During month-long field tests, the cooling ink achieved 37% electricity savings compared to traditional commercial white paints. Its non-porous nature also enables exceptional robustness against harsh environmental conditions, including mechanical deformation, surface abrasion, and UV exposure. These results represent a breakthrough in the practical implementation of sustainable daytime radiative cooling technologies. Finally, the fourth study establishes a numerical model for the system-level integration of water-based daytime radiative cooling panels with heat exchangers and cold storage to cool indoor air in residential buildings. The effects of different system design and operation parameters were studied, including water flow rate, number of heat exchangers, and operational schemes. Optimal water flow rates to maximize air cooling were identified to be 0.001–0.002 kg/(s⋅m2), with air temperature drops reaching 12.7°C for a typical single-family U.S. house. The feasible capital costs for the practical implementation of integrated radiative cooling systems were estimated for different U.S. cities. This chapter identifies key operational constraints in building energy management when using radiative cooling. In conclusion, this dissertation advances PDRC technology through multifunctional material innovation, cost-effective and adaptable manufacturing, and validated system integration strategies. These studies provide insights for deploying radiative cooling to enhance energy efficiency across building, industrial, and wearable applications, paving the way for addressing climate change.

Graduation Semester

2025-05

Type of Resource

Thesis

Handle URL

https://hdl.handle.net/2142/129715

Copyright and License Information

Copyright 2025 Kai Zhou

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