Application In Energy-efficient Windows Research Articles

Transparent, mechanically strong, thermally insulating cross-linked silica aerogels for energy-efficient windows

Silica aerogels are transparent and excellent thermal insulators; however, application in energy-efficient windows has been elusive. The main reason is fragility that renders handling and processing extremely difficult. One way to overcome the fragility issue of silica aerogels is via cross-linking technology, in which a polymer is applied conformally over their entire skeletal framework. Extremely strong materials may be obtained by that approach; however, the penalty is loss of transparency. This study was designed to reach a compromise among those competing requirements. Aerogels based on co-gelation of tetramethylorthosilicate (TMOS) and 3-aminopropyltriethoxysilane (APTES) were prepared and were cross-linked with a triisocyanate (Desmodur N3200A). The two independent variables, the total silane concentration in the sol and the concentration of the monomer in the cross-linking bath, were varied according to a full-factorial model. The nanostructure was characterized with SEM and SAXS. The porous structure with N2 sorption. Properties of interest with respect to the intended application were the thermal conductivity, the elastic modulus, and the haze. The latter has two components, from the bulk and the surface. Cross-linking places the polymer inside secondary aggregates that behave as core–shell particles with increased scattering, due to refractive index mismatch. Surface haze can be minimized by molding with clean glass plates and careful handling. Guided by our statistical model, we demonstrate optimal samples with bulk densities in the range of 0.25–0.33 g cm−3, porosities in the range of 76–83% v/v, bulk haze around 10%, Young’s modulus in the range of 30–70 MPa, and thermal conductivities in the range of 18–22 mW m−1 K−1. Those samples were strong enough to be machined with conventional tools (band saws, diamond cutters), they displayed sufficient clarity, and their thermal conductivity was lower than that of still air.

In situ fabrication of ZnO nanorods/Ag hybrid film with high mid-infrared reflectance for applications in energy efficient windows

Energy efficient windows are playing an important role in view of the fabrication of Energy-Saving and Eco-Friendly devices which show high energy efficiency among energy conservation buildings. In order to modulate middle-far range infrared radiation, a new strategy based on modulating semiconducting oxides ordered array structure and coating of metal element was proposed for energy efficient windows. In this work, ZnO nanorods/Ag hybrid film with high transmittance in visible region and high reflectance in mid-infrared region was prepared via hydrothermal method and silver-mirror coating above quartz glass that has great potential application in energy efficient windows for infrared radiation cooling. In detail, ZnO nanorods arrays were prepared via in situ fabrication with spin-coating method and hydrothermal process at low temperature. While Ag nanoparticles were coated on as-prepared ZnO nanorods via a silver-mirror method which is also in line with the concept of energy conservation. According to characterization results, ZnO nanorods were grown along the wurtzite c axis perpendicular to the quartz substrate, and Ag nanoparticles were coated on ZnO nanorods with a tight interrelation. ZnO nanorods/Ag hybrid film showed high transmittance of 62% in the visible region and high reflectance above 90% in the mid-infrared region. Therefore, ZnO nanorods/Ag hybrid film obtained in this work indicates excellent optical performance in visible transmission and mid-infrared reflection, and this hybrid film is illustrated to be good candidates for saving energy in the field of energy efficient windows.

Hydrothermal Synthesis of VO2 Polymorphs: Advantages, Challenges and Prospects for the Application of Energy Efficient Smart Windows.

Vanadium dioxide (VO2 ) is a widely studied inorganic phase change material, which has a reversible phase transition from semiconducting monoclinic to metallic rutile phase at a critical temperature of τc ≈ 68 °C. The abrupt decrease of infrared transmittance in the metallic phase makes VO2 a potential candidate for thermochromic energy efficient windows to cut down building energy consumption. However, there are three long-standing issues that hindered its application in energy efficient windows: high τc , low luminous transmittance (Tlum ), and undesirable solar modulation ability (ΔTsol ). Many approaches, including nano-thermochromism, porous films, biomimetic surface reconstruction, gridded structures, antireflective overcoatings, etc, have been proposed to tackle these issues. The first approach-nano-thermochromism-which is to integrate VO2 nanoparticles in a transparent matrix, outperforms the rest; while the thermochromic performance is determined by particle size, stoichiometry, and crystallinity. A hydrothermal method is the most common method to fabricate high-quality VO2 nanoparticles, and has its own advantages of large-scale synthesis and precise phase control of VO2 . This Review focuses on hydrothermal synthesis, physical properties of VO2 polymorphs, and their transformation to thermochromic VO2 (M), and discusses the advantages, challenges, and prospects of VO2 (M) in energy-efficient smart windows application.

Reflectance modulation of transparent multilayer thin films for energy efficient window applications

Spectrally selective glazing system attracts great attention for energy efficient window applications. In this study, multilayer films consisting of high/low/high (TiO 2/SiO 2/TiO 2) refractive index materials were prepared by sol–gel synthesis and spin coating process. Film thicknesses were examined by spectroscopic ellipsometry (SE) and focused ion beam (FIB) techniques, and refractive indices of TiO 2 and SiO 2 single layer films were also measured by SE. The reflectance spectra experimentally measured from multilayer films were in good agreement with the theoretical calculations by incorporating variable refractive index into the transfer matrix, so it is possible to modulate reflectance of multilayer films by controlling experimental variables for energy efficient transparent window applications.

Effects of Oxygen Flow on the Infrared Switching Properties of Vanadium Oxide Thin Films

Vanadium oxide (VOX) thin films have been deposited on glass substrates with different oxygen flows (3, 3.2, and 3.6sccm) by means of magnetron sputtering process. We found that for different oxygen flows, the change of the infrared transmittance can be reached as high as 57%, the transmittance contrast factor can be reached as high as 88%,and the phase transition temperature is decreased to 54 oC, it is an ideal material for application in energy-efficient windows. According to the X-ray diffraction results of the thin films, we observed that with the increase of oxygen flow, VO2 (200) diffraction peak decreases obviously.

Crystalline WO3 Nanoparticles for Highly Improved Electrochromic Applications

Electrochromic (EC) materials change their optical properties (darken/lighten) in the presence of a small electric potential difference, and are suitable for application in energy-efficient windows, antiglare automobile rear-view mirrors, sunroofs, displays, and hydrogen sensors. [1–4] The operation of conventional EC devices depends on the reversible electrochemical double injection of positive ions (H + ,L i + ,N a + ) and electrons into the host lattice of multivalent transition metal oxide materials, [5–10] with positive-ion insertion required to satisfy charge neutrality. However, diffusion of positive ions into the oxide layer is often slow, taking minutes to complete. Since the chemical diffusion coefficient of protons (DH+ )i s an order of magnitude larger than that of lithium ions (DLi+), EC systems based on proton electrolytes (e.g., aqueous H2SO4) are mandatory for display applications and preferred for other applications. Unfortunately, proton insertion currently results in rapid degradation of EC films. There are two important criteria for selecting an EC material. The first is the time constant of the ion-intercalation reaction, which is limited both by the diffusion coefficient and by the length of the diffusion path. While the former depends on the chemical structure and crystal structure of the metal oxide, the latter is determined by the material’s microstructure. [11] In the case of a nanoparticle, the smallest dimension is represented by the diffusion path length. Thus, designing a nanostructure with a small radius, while maintaining the proper crystal structure, is key to obtaining a material with fast insertion kinetics, enhanced durability, and superior performance. The second important criterion is coloration efficiency (CE), the change in optical density (OD) per unit inserted charge (Q), that is, CE= D(OD)/DQ. [12] A high CE provides

Optical properties of hafnium oxide thin films and their application in energy-efficient windows

Abstract Thin films of hafnium oxide were deposited by electron beam evaporation. The films were characterized using X-ray diffraction, X-ray photoelectron spectroscopy and normal incidence transmittance. The films were amorphous, stoichiometric, and transparent down to a wavelength of 300 nm. The optical properties of the films, including the refractive index, the absorption index and the bandgap, were determined. The refractive index, in the visible, was relatively high (1.89). The direct bandgap was found to be 5.41 eV. Absorption was insignificant for wavelengths above 250 nm. A heat mirror was built based on the hafnium oxide/silver/hafnium oxide/glass system. This heat mirror was found to be transparent in the visible with an average transmittance of 72.4%, and reflective in the near infrared (wavelength = 700–2000 nm) with an average reflectance of 67.0%. Such a heat mirror can be used in applications involving energy-efficient windows.