Dual-intelligent windows regulating both solar and long-wave radiations dynamically

Long, Linshuang; Yu, Hong

doi:10.1016/j.solmat.2017.05.022

Cited by 28 publications

(11 citation statements)

References 25 publications

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“…They are known as high efficiency radiative coolers or radiative windows if the cooler surface is partially transparent. Additionally, if the window can adjust its radiative properties in response to the changing environmental conditions such as ambient temperature and daylight illumination [25][26][27], or if it is capable of both cooling and heating, such windows are frequently referred to as intelligent or smart window [28].…”

Section: Introductionmentioning

confidence: 99%

“…Currently, there three main types of smart windows in development that use electrochromic, thermochromic, photochromic materials and combinations of thereof. Electrochromic materials employ reversible redox reaction that affects material's electronic transitions, and, as a consequence, the absorption profile of the solar spectra [28]. Several metal oxides have been reported for applications in smart windows among which the tungsten oxide (WO3) being the most popular one due to material's fast switching time between opaque and clear sates, as well as high visible light transmission in the clear state [40,41].…”

Section: Introductionmentioning

confidence: 99%

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Improving thermo-optic properties of smart windows via coupling to radiative coolers

et al. 2020

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In this work we first solve the radiative heat transfer problem in one dimension to perform a comparative analysis of the time averaged performance of the partially transparent radiative windows and radiative coolers. In doing so we clearly distinguish the design goals for the partially transparent windows and radiative coolers and provide optimal choice for the material parameters to realize these goals. Thus, radiative coolers are normally non-transparent in the visible, and the main goal is to design a cooler with the temperature of its dark side as low as possible relative to that of the atmosphere. For the radiative windows, however, their surfaces are necessarily partially transparent in the visible. In the cooling mode the main question is rather about the maximal visible light transmission through the window at which the temperature on the window somber side does not exceed that of the atmosphere. We then demonstrate that transmission of the visible light through smart windows can be significantly increased (by as much as a factor of 2) without additional heating of the windows via coupling of the windows to the radiative coolers using transparent cooling liquid that flows inside of the window and radiative cooler structures. We demonstrate that efficient heat exchange between radiative coolers and smart windows can be realized using small coolant velocities (sub 1mm/s for ~1m-large windows) or even using a purely passive gravitationally driven coolant flows between a hot smart window and a cold radiative cooler mounted on top of the window with only a minimal temperature differential (sub-1K) between the two. We believe that our simple models complimented with an in-depth comparative analysis of the standalone and coupled smart windows and radiative coolers can be of interest to a broad scientific community pursuing research in these disciplines.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Improving thermo-optic properties of smart windows via coupling to radiative coolers

et al. 2020

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“…FDTD simulation model. As FDTD gives an excellent scaling performance of the method as the problem size grows and is widely used in the research of nanophononics 33,[44][45][46] , FDTD simulations are conducted to optimize the thickness of each layer as well as the dimensions of the nano-cones and to analyze the optical performance. The real and imaginary parts of the complex refractive indices from 300-2,500 nm of the VO 2 and TiO 2 are taken from the references 23,47 .…”

Section: Methodsmentioning

confidence: 99%

Bio-inspired TiO2 nano-cone antireflection layer for the optical performance improvement of VO2 thermochromic smart windows

Liu

Tso

Lee

et al. 2020

Sci Rep

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Vanadium dioxide (VO 2) is a promising material for thermochromic glazing. However, VO 2 thermochromic smart windows suffer from several problems that prevent commercialization: low luminous transmittance (T lum) and low solar modulation ability (ΔT sol). The solution to these problems can be sought from nature where the evolution of various species has enabled them to survive. Investigations into the morphology of moths eyes has shown that their unique nanostructures provide an excellent antireflection optical layer that helps moths sharply capture the light in each wavelength from a wide angle. Inspired by this mechanism, a VO 2 thermochromic smart window coated with a TiO 2 antireflection layer with a novel nano-cone structure, is presented in this study to achieve high T lum and ΔT sol. Optimization for the key structure parameters is summarized based on the FDTD numerical simulations. The optimized structure exhibits a T lum of 55.4% with ΔT sol of 11.3%, an improvement of about 39% and 72% respectively compared to the VO 2 window without an antireflection layer. Furthermore, wide-angle antireflection and polarization independence are also demonstrated by this nano-cone coating. This work provides an alternative method to enhance the optical performance of VO 2 smart windows. Energy and environmental problems have become critical issues in modern society. It has been proven that buildings consume 20-40% of the total energy used. Most importantly, 60% of that energy is consumed to maintain thermal comfort by heating, ventilation and air conditioning (HVAC) systems 1. The huge consumption of energy by HVAC systems is mainly due to heat loss through the building envelope such as the roof, walls and windows. Among these building envelopes, approximately 50% of the energy is lost through windows, so more attention has been focused on energy efficient windows 2. Thermochromic smart windows are widely investigated because of their low cost and passive controllability of solar irradiance 3. Vanadium dioxide (VO 2) is one of the thermochromic materials to modulate transmittance of solar radiation because of its internal reversible phase change from metal (hot state) to insulator state (cold state) at a critical transition temperature of 68 °C 4. The phase change gives rise to an abrupt change of the near-infrared (NIR) transmittance, which renders VO 2 a promising candidate for thermochromic smart windows. To fulfill the demand of human vision and energy efficiency, improving luminous transmittance (T lum) and solar modulation ability (i.e. the difference of solar transmittance (T sol) between cold and hot states of materials or ΔT sol) simultaneously are key for the practical applications of VO 2 smart windows in buildings 5. Many efforts have been made to improve T lum and ΔT sol of thermochromic smart windows, such as chemical doping 6,7 , synthesizing VO 2 nanoparticles 8-11 and morphology modification 12-15. Among the different methods, depositing a planar antireflection layer is a commonly used solution to achi...

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“…They are known as high efficiency radiative coolers or radiative windows if the cooler surface is partially transparent. Additionally, if the window can adjust its radiative properties in response to the changing environmental conditions such as ambient temperature and daylight illumination [31][32][33], or if it is capable of both cooling and heating, such windows are frequently referred to as intelligent or smart window [34].…”

Section: Introductionmentioning

confidence: 99%

“…Currently, there three main types of smart windows in development that use electrochromic, thermochromic, photochromic materials and combinations of thereof. Electrochromic materials employ reversible redox reaction that affects material's electronic transitions, and, as a consequence, the absorption profile of the solar spectra [34]. Several metal oxides have been reported for applications in smart windows among which the tungsten oxide (WO3) being the most popular one due to material's fast switching time between opaque and clear sates, as well as high visible light transmission in the clear state [46,47].…”

Section: Introductionmentioning

confidence: 99%

Simple models for the operation of partially transparent radiative windows and their comparison to the radiative coolers

Skorobogatiy¹,

Caloz²,

Zhung³

2019

Preprint

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In this work we solve approximately the radiative heat transfer problem in one dimension to perform a comparative analysis of the time averaged performance of the partially transparent radiative windows and radiative coolers. Our physical model includes the atmosphere, the window, and the backwall that are all in the thermal equilibrium with each other, and that can exchange energy via radiative heat transfer or convection. Moreover, we use a simplified two-state model for the optical properties of an atmosphere and a window material which assumes two distinct sets of the optical reflection/absorption/transmission parameters in the visible/near-IR versus mid-IR spectral ranges. Furthermore, we have distinguished the design goals for the partially transparent windows and radiative coolers and provided optimal choice for the material parameters to realize these goals. Thus, radiative coolers are normally non-transparent in the visible, and the main goal is to design a cooler with the temperature of its dark side as low as possible compared to that of the atmosphere. For the radiative windows, however, their surfaces are necessarily partially transparent in the visible. In the cooling mode, therefore, the main question is about the maximal visible light transmission through the window at which the temperature on the window somber side does not exceed that of the atmosphere. We believe that our simple physical models complimented with an in-depth comparative analysis of the radiative windows and coolers can be of interest to a number of scientists and engineers pursuing research in these disciplines.

show abstract

Dual-intelligent windows regulating both solar and long-wave radiations dynamically

Cited by 28 publications

References 25 publications

Improving thermo-optic properties of smart windows via coupling to radiative coolers

Improving thermo-optic properties of smart windows via coupling to radiative coolers

Bio-inspired TiO2 nano-cone antireflection layer for the optical performance improvement of VO2 thermochromic smart windows

Simple models for the operation of partially transparent radiative windows and their comparison to the radiative coolers

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