Chameleon-inspired Self-adaptive Daytime Passive Radiative Coolers with Cooling Power Modulation Ability for Building Applications

Project: Research

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Description

In many cities, air-conditioning (AC) is a major source of electricity consumption in buildings. Daytime passive radiative coolers (DPRCs) require neither electricity nor refrigerants, ideal for smart-green buildings. By reflecting sunlight and emitting mid-infrared thermal radiation to the cold universe, net cooling is achieved by DPRCs in all-seasons. Unfortunately, current DPRCs lack cooling power modulation, leading to undesirable cooling in winter. To resolve this, a novel self-adaptive daytime passive radiative cooler (SDPRC) with solar reflectivity regulationinduced cooling power modulation ability (CPMA) inspired by chameleons is proposed. The SDPRC, in a hierarchically porous structure, displays pure-white and possesses high solar reflectivity in summer, achieving self-cooling for saving AC energy. Conversely, for warmth in winter, core-shell structured inhomogeneous thermochromic microparticles (ITMs) in the porous structure cause the SDPRC to automatically switch to a dark color to absorb solar heat. This project aims to develop SDPRCs and to gain scientific understanding of light scattering in porous structures with ITMs. Our preliminary results show the solar reflectivity and cooling power of a green-SDPRC are 94% and 111W/m2in summer, respectively, while in winter, solar reflectivity of 79% and heating power of 81W/m2are achieved, exhibiting a promising CPMA.  Despite these encouraging results, several academic challenges need addressing since the fundamental mechanism of light scattering in hierarchically porous structures with ITMs is not fully-understood. Notably, a SDPRC with CPMA remains undiscovered. This study will first develop an optical model describing light propagation in SDPRCs that considers parameters, including pore size distribution, porosity and thickness of the porous structures, and various types and concentrations, and particle size distribution of the ITMs, for estimating the optical properties of SDPRCs. Using the simulated optical spectra from the optical model, a heat transfer model will be built to estimate the cooling power and CPMA of SDPRCs. Additionally, a relationship among those parameters against the color, cooling power and CPMA will be determined. Guided by the models, the optimized SDPRC will be fabricated and characterized. Both models will be verified experimentally. A field test will be conducted to examine the cooling power and CPMA of the optimized SDPRC under different weather conditions. To evaluate the energy-saving performance, several model houses equipped with different coolers and the optimized SDPRC will be built. This study will enhance the fundamental understanding of the optics of hierarchically porous structures with ITMs, and realize the CPMA of the SDPRC for its versatility in different seasons, opening a new avenue for the development of DPRCs. 

Detail(s)

Project number9043303
Grant typeGRF
StatusNot started
Effective start/end date1/01/23 → …