Variation of Thermochromic Glazing Systems Transition Temperature, Hysteresis Gradient and Width Effect on Energy Efficiency

Due to increasing pressure to reduce the energy demand in buildings, thermochromic thin film based glazing has become a recognized potential solution due to the intrinsic ability to modulate the solar heat gain of a window as a function of the materials temperature. These “intelligent” glazings have been investigated for several years, and it has been found that, through variation of synthetic route, the thermochromic properties (transition temperature, hysteresis gradient and width) can be altered; however, less attention has been applied to how such alterations affect the overall energy savings attributed to the materials. In this study the building simulation software EnergyPlus TM has been used to model a series of idealized thermochromic spectra in a series of different environments to evaluate their energy saving potential against both clear glass systems and industry standards. The idealized spectra are used to see what effect each of the materials thermochromic properties and therefore elucidate which are the most important with respect to the energy saving properties. It was found that the best thermochromic materials were those with a narrow sharp hysteresis and a low transition temperature and result in an increase in energy saving between 30%–45% across the different environments compared to clear glass systems

The effect of transition hysteresis width in thermochromic glazing systems

Thermochromic glazing theoretically has the potential to lead to a large reduction in energy demand in modern buildings by allowing the transmission of visible light for day lighting whilst reducing unwanted solar gain during the cooling season, but allowing useful solar gain in the heating season. In this study building simulation is used to examine the effect of the thermochromic transition hysteresis width on the energy demand characteristics of a model system in a variety of climates. The results are also compared against current industry standard glazing products. The results suggest that in a warm climate with a low transition temperature and hysteresis width energy demand can be reduced by up to 54% compared to standard double glazing

Chemical vapour deposition of metal oxides and phosphides.

This thesis investigates the deposition of thin films of main group metal phosphide and main group metal oxide compounds on glass substrates by the use of dual source atmospheric pressure chemical vapour deposition. Binary phosphide systems with tin, germanium, silicon, antimony, copper or boron have been examined. Binary oxide systems of gallium, antimony, tin or niobium have also been investigated. Additionally these systems were deposited on gas sensor substrates and evaluated as metal oxide semiconductor gas sensors. Halides were used as the metal precursor, RXPH3.X (R = Cychex or Phenyl) were used as phosphorous precursors and either methanol or ethyl acetate were used as oxygen precursors. These coatings showed good uniformity and coverage and the films were adherent passing the Scotch tape test. The tin phosphide films were opaque in appearance with some signs of birefringence due to differential thickness effects. Germanium phosphide and the gallium, antimony, niobium and tin oxide systems were all transparent, once again birefringence was observed. The films produced from the antimony phosphide and silicon phosphide systems were opaque, grey and metallic. Additional work was conducted on the deposition on a variety of alkali metal and alkaline earth metal fluorides on glass substrates using aerosol assisted chemical vapour deposition. In all cases the films were very powdery and were easily wiped off of the substrate. A number of depositions were carried out combining the aerosol and atmospheric pressure methodologies. A tin oxide film was produced from the atmospheric pressure chemical vapour deposition reaction of tin tetrachloride and ethyl acetate. The film contained tungsten, which was introduced into the reaction using a polyoxometalate delivered via aerosol assisted chemical vapour deposition. Films were analysed using Raman microscopy, X-ray diffraction, scanning electron microscopy, energy dispersive analysis of X-rays, electron probe microanalysis, X-ray photoelectron spectroscopy and ultra violet and visible spectroscopy

Thin films for advanced glazing applications

© 2016 by the authors.Functional thin films provide many opportunities for advanced glazing systems. This can be achieved by adding additional functionalities such as self-cleaning or power generation, or alternately by providing energy demand reduction through the management or modulation of solar heat gain or blackbody radiation using spectrally selective films or chromogenic materials. Self-cleaning materials have been generating increasing interest for the past two decades. They may be based on hydrophobic or hydrophilic systems and are often inspired by nature, for example hydrophobic systems based on mimicking the lotus leaf. These materials help to maintain the aesthetic properties of the building, help to maintain a comfortable working environment and in the case of photocatalytic materials, may provide external pollutant remediation. Power generation through window coatings is a relatively new idea and is based around the use of semi-transparent solar cells as windows. In this fashion, energy can be generated whilst also absorbing some solar heat. There is also the possibility, in the case of dye sensitized solar cells, to tune the coloration of the window that provides unheralded external aesthetic possibilities. Materials and coatings for energy demand reduction is highly desirable in an increasingly energy intensive world. We discuss new developments with low emissivity coatings as the need to replace scarce indium becomes more apparent. We go on to discuss thermochromic systems based on vanadium dioxide films. Such systems are dynamic in nature and present a more sophisticated and potentially more beneficial approach to reducing energy demand than static systems such as low emissivity and solar control coatings. The ability to be able to tune some of the material parameters in order to optimize the film performance for a given climate provides exciting opportunities for future technologies. In this article, we review recent progress and challenges in these areas and provide a perspective for future trends and developments.Işıl Top thanks TUBITAK for the provision of funding for a studentship. Shuqun Chen thanks the China Scholarship Council for the provision of a studentship

The gas sensing properties of some complex metal oxides prepared by self-propagating high-temperature synthesis

The gas-sensing properties of spinel and orthorhombic ferrites (NiFe2O4, CoFe2O4 and LaFeO3 respectively) as well as cubic nickel–zinc stannates Zn2 − xNixSnO4 (with x = 0, 0.8) prepared by self-propagating high-temperature synthesis (SHS) are reported. This is the first report of using an SHS derived powder for gas sensing applications. The gas response of the materials was investigated against a range of gases (ethanol, ammonia, propane, CO, ethane, ethene) at a variety of operating temperatures. Good gas response behavior was found in the case of the cubic nickel–zinc stannates with excellent selectivity toward ethanol

Aerosol assisted chemical vapour deposition of Ga-doped ZnO films for energy efficient glazing: effects of doping concentration on the film growth behaviour and opto-electronic properties

S.Q. Chen would like to thank the China Scholarship Council/Queen Mary University of London Joint PhD scholarship program. G.C. and D.B. kindly acknowledge the financial support from Padova University PRAT 2010 project (no. CPDA102579) and grant no. CPDR132937/13 (SOLLEONE)

VO2/TiO2 bilayer films for energy efficient windows with multifunctional properties

Vanadium dioxide/titanium dioxide bilayer films have been investigated as a thermochromic coating for application as intelligent window glazings for buildings. The nanostructured VO2 and TiO2 films were deposited on fluorine doped tin oxide coated glass substrates using electric field assisted aerosol assisted chemical vapour deposition (ElFi-AACVD) and sol-gel spin coating, respectively. Their thermochromic properties were investigated using scanning electron microscopy, X-ray diffraction, variable temperature UV/Vis/NIR and X-ray photoelectron spectroscopies. Compared to bare VO2 films, the VO2/TiO2 bilayer films exhibit an increase in visible light transmittance of up to 30%, an increase in integrated luminous transmisttance, with values up to 66%, and a higher transmittance modulation in the near infrared of up to 20% at the thermochromic transition temperature. The TiO2 top layer not only enhances visible light transmittance, but also serves to protect the VO2 bottom layer from oxidation. The bilayer films are shown to exhibit photo-induced super-hydrophilicity. These properties are affected by the morphology of the VO2 under-layer

Incorporation of Ag nanowires in CuWO 4 for improved visible light-induced photoanode performance

We report the sol–gel synthesis of a CuWO4 (Eg � 2.0–2.15 eV) thin film loaded with Ag nanowires. The incorporation of Ag nanowires into the semiconductor matrix significantly improves the performance of CuWO4 as a photoanode for use in photochemical water splitting (PEC). Here, we have developed a planar electrode to test the photoactivity of the catalyst using standard electrochemical procedures under simulated solar light. The sol–gel synthesis of CuWO4 is modified such that we add Ag nanowires during sol aging. We demonstrate that there is negligible change to the CuWO4 matrix microstructure, morphology or crystal structure. When we compare the pristine CuWO4 to the material with Ag nanowires embedded in the CuWO4 matrix there is a fourfold improvement of photocurrent at 1.23 V vs. NHE to ca. 1.5 mA cm2 (pH 9) under simulated AM1.5G illumination. This photocurrent is very competitive against more well developed photoanode structures when consideration for surface area is allowed. The Ag nanowires increase carrier mobility film enabling a sufficiently thick sample of catalyst, measured at 750 nm, to effectively harvest incident light. The addition of the Ag nanowires removes the plateau region found for CuWO4 further indicating that there is a good flow of carriers to the surface of the catalyst, a significant improvement as carrier mobility has been shown to be low in CuWO4. The Faradaic efficiency of the catalyst was measured at 31%. Our flat band potential is found to be 0 vs. NHE. The ability to make a highly photoactive catalyst using a simple chemical process opens up opportunities in a wide range of areas that focus on PEC and other light harvesting processes