Bilayer porous polymer for efficient passive building cooling

Pang

et al. 2021

EcoMat

100

Passive daytime radiative cooling (PDRC) dissipates terrestrial heat to the extremely cold outer space without using any energy input or producing pollution. It has the potential to simultaneously alleviate the two major problems of energy crisis and global warming. In this review, we summarize general strategies implemented for achieving PDRC and various applications of PDRC technologies. We first introduce heat transfer processes involved in PDRC, including radiative and nonradiative heat transfer processes, to evaluate the PDRC performance. Subsequently, we summarize the general material designs used for controlling PDRC performance, such as tuning the thermal mid-infrared emittance and solar reflectance. Finally, we discuss the diverse applications of PDRC technologies to overcome problems in space cooling, solar cell cooling, water harvesting, and electricity generation.

{\overset{true¯}{R}}_{solar}

Section: Materials Designs For Pdrcmentioning

confidence: 99%

Passive daytime radiative cooling: Fundamentals, material designs, and applications

Pang

et al. 2021

EcoMat

100

Adv Materials Technologies

“…The hierarchical pores in the coating can efficiently reflect solar rays and enhance the thermal infrared emissivity. [32] The crosssectional optical images (Figure 2d,e) obtained by an ultra-deep 3D microscope show the uniform white P(VdF-HFP) HP coating on the top surface of the fabric. It can be found the pore sizes of the P(VdF-HFP) HP polymer coating (Figure 2f) were mainly distributed in the sunlight band (0.3-2.5 µm).Therefore, the P(VdF-HFP) HP polymer coating could effectively scatter the sunlight and achieve a high light reflectivity.…”

Section: Preparation and Morphology Characterization Of The Fabricmentioning

confidence: 95%

Preparation of Passive Daytime Cooling Fabric with the Synergistic Effect of Radiative Cooling and Evaporative Cooling

Sun

Javed

et al. 2021

µm) and emitting thermal radiation into the chilly outer space through the atmospheric transparency window (8-13 µm). [3][4][5][6][7][8] To achieve desired cooling effect, PDRC structures should possess a sufficiently high solar reflectance (R solar ) to minimize the heat gain from the environment and a superior long-wave IR emittance (ε LWIR ) for releasing excess heat to the cold outer space. [9][10][11] A variety of PDRC coolers have been proposed and exhibit efficient cooling effect. [12][13][14][15][16][17][18][19][20] Raman et al. [16] presented a nanophotonic structured PDRC cooler consisting of seven alternating layers of hafnium dioxide (HfO 2 ) and silica (SiO 2 ), which could cool the rooftop 4.9 °C below ambient air temperature under direct sunlight irradiation (>850 W m −2 ). Zhai et al. [19] reported a randomized glass-polymer hybrid PDRC film by embedding SiO 2 microspheres in the polymethylpentene matrix and backing the film with a silver coating. It is claimed the prepared PDRC film exhibited a noontime radiative cooling power of 93 W m −2 under direct sunshine. Furthermore, textile as a high-strength flexible material has received widespread attention in many fields. [21,22] Some radiative cooling textiles have also been successfully prepared. Wang et al. [23] presented an electrospinning method to fabricate the flexible membrane radiator, which consists of polyvinylidene fluoride/tetraethyl orthosilicate fibers and SiO 2 microspheres randomly distributed across its surface. Cai et al. [24] reported a spectrally selective nanocomposite textile for radiative outdoor cooling by embedding zinc oxide (ZnO) nanoparticles into polyethylene (PE). Zeng et al. [25] developed a multilayer PDRC metafabric which could cool a human body ≈4.8 °C lower than that covered by a regular cotton fabric in the practical application tests. These PDRC systems show reliable daytime radiative cooling performance. However, most of the PDRC devices suffer from complex preparation process and high cost.Besides radiative cooling, evaporative cooling is also an effective alternative to achieve passive cooling by dissipating heat through water evaporation. Evaporative cooling is a simple, inexpensive, and green strategy to cool the human and buildings without additional energy input. [26][27][28] Li et al. [29] reported an evaporative cooling fabric by integrating superabsorbent

“…When compared to photonic structures, polymer‐based radiation cooling materials can not only reduce the cost but also greatly improve the extensibility and flexibility. At present, porous polymer materials, [ 8–11 ] aerogels, [ 12–14 ] coatings, [ 15–21 ] fabric, [ 22,23 ] nanostructured materials, [ 16,24–27 ] white cooler wood, [ 28 ] composite cooling materials, [ 11,29,30 ] and dielectric microsphere materials [ 31,32 ] have been widely studied. For example, Zhu et al.…”

Section: Introductionmentioning

confidence: 99%

“…When compared to photonic structures, polymer-based radiation cooling materials can not only reduce the cost but also greatly improve the extensibility and flexibility. At present, porous polymer materials, [8][9][10][11] aerogels, [12][13][14] coatings, [15][16][17][18][19][20][21] fabric, [22,23] nanostructured materials, [16,[24][25][26][27] white cooler wood, [28] composite cooling materials, [11,29,30] and dielectric microsphere materials [31,32] have been widely studied. For example, Zhu et al demonstrated a hierarchically designed nanofibre-based film, which allows for a high reflectivity of 96.3% in the 0.3-2.5 μm wavelength range and a selective emissivity of 78% in the 8-13 μm wavelength range.…”

Section: Introductionmentioning

confidence: 99%

Fabrication of Hydrophobic Multilayered Fabric for Passive Daytime Radiative Cooling

Sun

Javed

et al. 2022

Macro Materials & Eng

Passive daytime radiative cooling (PDRC) has attracted great attention recently due to its high potential for reducing global energy consumption. However, PDRC materials are easily contaminated in practical applications, which will seriously attenuate their long-term cooling performance. In this work, a multilayered PDRC fabric that is composed of polydimethylsiloxane (PDMS), polymethyl methacrylate (PMMA), and cotton is shown. This multilayered fabric displays a high solar reflectivity (0.94) and an appropriate atmospheric window emissivity (0.79). A practical application test demonstrates the glass covered by this PDRC fabric can lower the temperature up to 7.8 °C under a solar intensity of ≈495 W m −2 . Meanwhile, the multilayered PDRC fabric exhibits self-cleaning property due to its high water contact angle of 118°. Rolling water can effectively remove the contaminants on the fabric surface. It is believed that this multilayered fabric is a promising material to alleviate the energy crisis and reduce greenhouse gas emissions.