The effect of glazing shape upon the thermal performance of buildings

The great incidence that glazing has in a building energy conservation makes it one of the most important parameters to be taken into account especially in commercial buildings, where the surface occupied by glass areas is very important. So, different shapes of glass areas and their influence in the energy consumption of a commercial building are studied in this paper. Horizontal glazing (with different heights) and vertical glazing (with the same area as the horizontal ones), separated by opaque areas are considered in a base case building. A traditional wall and a curtain-wall are considered, and the different annual consumptions per conditions unit surface, both in winter and summer, are obtained.     

Evaluation of the thermal performance indices of a ventilated double window through experimental and analytical procedures: Uw-values

Simulations to evaluate energy demand for heating and cooling and thermal comfort are becoming more and more common place in the building design process, at least in the most complex cases. In all detailed or simplified calculations, to analyse heat transfer to and from a building, several input parameters are needed. The inputs for the simulation of a whole building are at least the building geometry, the building envelope thermal indices (like thermal transmittance or the solar heat gain coefficient) and typical local climatic data. In a ventilated double window, the air flow through the channel between the two windows makes its thermal performance highly dynamic and dependent on the air flow characteristics. For a whole building simulation, single coefficients or easily calculated coefficients are needed for each facade system, including ventilated systems. In this paper, equivalent thermal transmittance coefficients for a ventilated double window are assessed and presented. For that, experimental measurements in the absence of solar radiation (night period) were used to identify tendencies and validate calculations. Furthermore, simulations were done in order to estimate the U_w-values of the ventilated double window under different windows configuration and different air flow rates. These values can then be used in whole building simulation programmes.     

Effect of rapid thermal annealing on optical properties of zinc sulphide thin films

Zinc sulphide (ZnS) thin films were prepared on clean surface glass substrates by thermal evaporation under pressure of 10^?5?Torr. Thickness of thin films was uniform 55?nm measured by ellipsometry. These films were also kept into a quartz glass tube for rapid thermal annealing at 30 and 60?s by using a 500?W halogen lamp for crystalline the structure. The cubic structure of the films was verified by X-ray diffraction and the intensity of predominant peak increases with annealing time. The optical absorption study was carried out by UV–ViS–NIR spectrometer in the range of 200–800?nm. The optical band gap changes from 3.48 to 3.08?eV, with rapid thermal annealing. Thermo electric power studies confirm the n-type nature of ZnS thin films and thermoelectric power increases with increase in temperature. This study is important because ZnS is potentially important material for antireflection coating and window layer material in hetero-junction solar cells.     

Synergic effects of thermal mass and natural ventilation on the thermal behaviour of traditional massive buildings

The energy policies about energy efficiency in buildings currently focus on new buildings and on existing buildings in case of energy retrofit. However, historic and heritage buildings, that are the trademark of numerous European cities, should also deserve attention; nevertheless, their energy efficiency is nowadays not deeply investigated. In this context, this study evaluates the thermal performance of a traditional massive building situated in a Mediterranean city. Dynamic numerical simulations were carried out on a yearly basis through the software DesignBuilder, both in free-running conditions and in the presence of an air-conditioning (AC) system. The results highlight that the massive envelope of traditional residential buildings helps in maintaining small fluctuations of the indoor temperature, thus limiting the need for AC in the mid-season and in summer. This feature is highly emphasised by exploiting natural ventilation at night, which allows reducing the building energy demand for cooling by about 30%.The research also indicates that, for Mediterranean climate, the increase in thermal insulation does not always induce positive effects on the thermal performance in summer, and that it might even produce an increase in the heat loads due to the transmission through the envelope.     

Doping, vacuum annealing, and thickness effect on the physical properties of zinc oxide films deposited by spray pyrolysis

Gallium, aluminum, and indium-doped ZnO (ZnO:Ga, ZnO:Al, and ZnO:In) films have been deposited by the chemical spray method on sodocalcic substrates. The effect of different dopant elements, a post-annealing treatment in vacuum, and the film thickness on the electrical, optical, structural, and morphological properties of the films has been investigated. The best electrical properties were observed in the thickest indium-doped ZnO films; the lowest electrical resistivity was of the order of 10⁻³ Ω cm. In general, the optical transmittance value in the visible spectrum oscillated around of 87% in the thinnest films. The structural and morphological properties of ZnO:Ga and ZnO:Al films are similar, as in both cases the (0 0 2) orientation is dominant on the rest of the peaks, and both surfaces have a rough appearance. In the case of ZnO:In films, the (1 0 1) was the preferential growth orientation, and the surfaces seem to be smoother than the corresponding ZnO:Ga and ZnO:Al films.     

The effect of surface treatment on omni-directional efficiency of the silicon solar cells with micro-spherical texture/ITO stacks

A “bottom-up” surface texturing method based on nozzle-sprayed microspheres and spin-coated dielectric film has been proposed. The fill factor was improved by the use of indium tin oxide (ITO) as an antireflection coating (ARC) due to an increased effective area for carrier collection. The pretreatment using HCl prior to ITO deposition was found to suppress the formation of interfacial oxide at the ITO/Si junction. An enhancement in the short-wavelength response (400-600 nm) and an improvement in the short-circuit current (J_SC) were accomplished. The difference in the efficiency (Δη) between the cells fabricated with ITO incorporating micro-spherical textures (MSTs) and those by KOH texturing was 13.5% at a light incident angle of 60°, comparatively larger than the difference in efficiency of 7.4% observed at normal incidence. These results demonstrate the superior omnidirectional antireflection property of the ITO+MST structure.     

Study of the electrical and junction properties of ITO thin films deposited on CdTe and InP substrates

Thin films of indium tin oxide (ITO) have been deposited on fused quartz substrates by the spray deposition and rf-magnetron sputtering methods and their optical and electrical properties investigated. The junction properties of fabricated ITO/pCdTe and ITO/pInP structures have also been studied and their electrical properties presented. It is established that the deposited ITO films have a lattice constant of 10.14 Å and grow in cubic modifications along the (400) direction. Their transmittance value rises up to between 85% and 90% and extends well beyond the visible range of the spectrum. In the forward direction of the ITO/pCdTe structure, it is suggested that tunnelling dominated processes determine the current flow mechanism. Recombination currents at the interface region and thermionic-emission currents, however, dominate in the ITO/pInP structure at low bias and high bias respectively. The two structures can best be described as heterojunctions.     

Evaluation of the aging behavior of ethylene copolymer films for solar applications under accelerated weathering conditions

Ethylene copolymers based on acrylic acids and acrylates are an interesting alternative to ethylene(vinylacetate) (EVA) for photovoltaic (PV) encapsulation. These materials provide similar or better mechanical and optical properties and a slightly better aging behavior, but without the formation of corrosive acetic acid during aging, which is particularly of importance in PV applications. The focus of the research work was to evaluate and screen the aging behavior of ethylene copolymers containing different types of comonomers for solar applications. To investigate the intrinsic weathering behavior of the materials, unstabilized films with comonomer contents around 10% were exposed to temperature, humidity and solar radiation. Special attention was given to the optical and mechanical properties. All investigated films showed high transparency in the solar range with hemispheric transmittance values above 91%. Regarding mechanical properties, the ethylene copolymer films exhibited a highly ductile behavior and high flexibility. Similar degradation behavior could be observed for all investigated films. Due to formation of chromophoric degradation products, yellowing could be observed and hemispheric transmittance values dropped slightly to values between 88.5 and 90.5%. The unstabilized films showed significant embrittlement due to weathering. After 750 h of weathering both strain-at-break and stress-at-break values of all ethylene copolymer films dropped significantly below 50% of the initial values.     

A simplified method for modelling the effect of blinds on window thermal performance

An approximate method is presented for predicting the effect of a louvered blind on the centre‐glass thermal performance of a fenestration. The method combines a one‐dimensional heat transfer model with data from a numerical simulation of the window and blind. Sample results for a blind mounted on the indoor surface of a window show the effect of blind slat angle on heat transmission. Both summer and winter conditions are considered. The results show that a louvered blind can improve the U‐value of a standard double‐glazed window by up to 37%. Also, the radiation heat exchange with the room can be dramatically reduced (by up to 60%), which will improve the level of occupant comfort. However, there was found to be a trade‐off between U‐value and occupant comfort; placing the blind closer to the window improves the U‐value, but increases the radiation heat exchange with the room. The predictions from the present simplified method compare well with results from a full two‐dimensional computational fluid dynamics solution of the conjugate blind/window interaction. Copyright © 2005 John Wiley & Sons, Ltd.     

Electrical and thermal transport properties of vanadium oxide thin films on metallic bipolar plates for fuel cell applications

We have focused on the in-depth comparative evaluation of the suitability of electrically-induced thermal transport characteristics of highly disordered vanadium oxide thin films deposited onto metallic bipolar plates as an expeditious self-heating source for the successful cold-start of fuel cells in a subfreezing environment. To achieve this, sol–gel derived vanadium oxide thin films on the non-polished surface of 316L austenitic and 446M ferritic substrates have been fabricated by a dip-coating process. The effects of electrical properties on thermal energy dissipation rate of the as-synthesized thin films deposited onto 316L and 446M stainless steel plates were firstly investigated and compared with each other. Subsequently, a series of physical, chemical, and structural analyses of the thin films have been performed using several analytical techniques such as the ASTM D3359, the ASTM D5946, XPS, and FE-SEM. The most important finding of this study was that the electrical resistivity of the thin films on 446M ferritic substrate was extremely low on a level of 4.8% of the 316L sample at −20 °C, and then the surface temperature rise of the thin film on 316L austenitic substrates was approximately 21.8 times greater than that of 446M ferritic substrates under simulated cold starting conditions (i.e., at a current density of 0.1 A·cm⁻² at −20 °C). Therefore, we concluded that vanadium oxide thin films on 316L austenitic stainless steel plates appears to be more applicable than those of 446M ferritic substrates for the cold-start enhancement of fuel cells from the practical point of view.     

Effect of thermal annealing on the structural and optical properties of nanostructured zinc oxide thin films prepared by pulsed laser ablation

Zinc oxide (ZnO) films are prepared by pulsed laser ablation, on an optically flat quartz substrate for different deposition time. The influence of annealing temperature, on the structural and optical properties of ZnO films is investigated systematically using X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX), scanning electron microscopy (SEM), atomic force microscopy (AFM), Raman spectra, UV-vis spectroscopy and photoluminescence spectroscopy (PL). The XRD pattern shows that the as-deposited films are amorphous and the annealed films are polycrystalline. The average size of the crystalline grains varies from 9 to 26 nm in the films. The SEM and AFM images reveal uniform distribution of grains in the films and the grains are in the nanoscale dimension. Raman spectra suggest the hexagonal wurtzite phase for the ZnO films. The UV-visible spectra show an increase in transmittance with annealing temperature. The observation of very intense PL emission from the films annealed at 773 K, suggest the suitability of these films for applications as light emitters in the visible region. The ability to produce the stochiometric ZnO thin films with reproducible structural, morphological and optical characteristics should be useful as a suitable window material for practical industrial solar cell and display devices.     

Influence of substrate temperature on the properties of laser ablated indium tin oxide films

Nanocrystalline indium tin oxide films are deposited in a reactive oxygen atmosphere with background pressure at 0.02 mbar on glass substrate at different substrate temperatures (T_s) ranging from 300 to 573 K using pulsed laser deposition technique. The films are characterized using GIXRD, AFM and UV–visible spectroscopy to study the effect of substrate temperature on the structural and optical properties of films. The XRD patterns suggest that the films deposited at room temperature are amorphous in nature and the crystalline nature of the films increases with increase in substrate temperature. The thickness of the film decreases with increase in substrate temperature. The AFM data show that substrate temperature plays a dominant role on the surface morphology of the films. UV–visible spectra show that all the deposited ITO films exhibit a direct allowed transition. The higher value of optical band gap obtained for the films may be attributed to quantum confinement effect. The films deposited at higher substrate temperatures show higher value of transmittance.     

The investigation of the effect of thermal barrier coating on the performance of Stirling engine

The shuttle heat transfer is one of the reasons reducing the performance of Stirling engines. This study is concerned with the reduction in shuttle heat transfer by coating the displacer. The displacer of a gamma type Stirling engine was coated with a layer of yttria‐stabilized zirconia (YSZ), and the effect of the coating on the engine performance was evaluated by comparing speed‐power and speed‐torque characteristics of the engine with coated and uncoated displacers. Characteristics were obtained for 700, 800 and 900°C heater temperatures. At each stage of the heater temperature, the charge pressure ranged from 1 to 3.5 bars with 0.5 bar increments. At 900°C heater temperature and 3 bars charge pressure, the shaft power before coating was 34.9 W, after coating the power increased to 43.8 W, which corresponds to a 25% increment. The temperature applied to the engine did not cause any damage on the coating layer. Copyright © 2008 John Wiley & Sons, Ltd.     

An effect of hydrogenation on the photoemission of amorphous SiCN films

The structure, chemical bonding and photoemission of amorphous hydrogenated silicon carbonitride (a-SiCN:H) films deposited by plasma-enhanced chemical vapor deposition (PECVD) using hexamethyldisilazane as a main precursor at different hydrogen flow rates are studied. Film properties are characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), absorption optical spectra and photoluminescence (PL). The photoluminescence spectra were presented by four photoemission bands centered at 441–451, 489–496, 530–535 and 577–601 (in nm). To explain structural and photoluminescence properties of the deposited films, first-principles molecular dynamics simulations of un-hydrogenated and hydrogenated silicon carbonitride samples were carried out. Based on experimental and theoretical results a possible explanation of the photoemission of the deposited films and its evolution with increasing hydrogen flow rate was done.     

Chemically sprayed ZnO:F thin films deposited from diluted solutions: Effect of the time of aging on physical characteristics

Transparent and conductive fluorine-doped zinc oxide (ZnO:F) thin films were deposited on glass substrates by the chemical-spray technique starting from a diluted solution of zinc acetate and hydrofluoric acid. The effect of the aging time of the starting solution on the electrical, structural, morphological and optical characteristics of ZnO:F thin films was observed and analyzed. The resistivity of the ZnO:F thin films decreases as a more aged solution is used, reaching a saturation value of 6×10⁻² Ω cm. X-ray diffraction reveals that the films are polycrystalline in nature with a (1 0 0) preferential growth in almost all the cases. High-resolution scanning electron microscopy clearly reveals that the films are composed of nanoparticles of spherical shape, whose average diameter is in the order of 15 nm that matches well with the crystallite size calculated from X-ray diffraction. This result shows that fluorine incorporation effectively inhibits grain growth. This, in turn, produces a porous structure. Also, the increase in the time of aging enhances slightly the transmittance of the films.     

Optical and structural properties of the sol-gel-prepared ZnO thin films and their effect on the photocatalytic activity

ZnO thin films were obtained by the sol-gel method, using the dip-coating procedure. Glass slides were used as substrates. The sintering temperature (T_s) was varied in the range of 200-600 °C in intervals of 50 °C, in an open atmosphere. Films with 1 and 5 coatings were prepared for each T_s. An increase of the grain size from 10 to 34 nm as the T_s increased was observed from X-ray diffraction measurements. The thickness of the films prepared starting from five coatings, decreased by 36% when T_s increased, and denser films were obtained. This result was corroborated with the refractive index values, calculated from the UV-Vis transmission spectra. The films were tested as a photocatalyst by the photobleaching of methylene blue in an aqueous solution under UV light exposure during 5 h. The photocatalytic activity (PA) increased with T_s, around 72% for the films with one coating and 66% for those with five coatings. The samples with one coating and a T_s=500 °C showed the best PA. However, the glass substrate had a negative effect on the PA for T_s>500 °C, even when the surface morphology of the samples showed an increase in roughness when T_s increased. The observed negative effect can be due to the presence of an amorphous compound formed by Si, Zn and O at the glass-ZnO interface.     

Hydrogen effect on the optical and electrical properties of metal oxide and nitride thin films

Effect of hydrogen introduction into some metal oxide and nitride thin films was examined. Modification of electrical and optical properties by hydrogen introduction was examined on SnO₂${}_2$, Sn–GeO₂${}_2$, Ge–CdO₂${}_2$, ZnO. Electrical resistance could be reduced in some films without loosing their transparence to the visible light. Hydrogen introduction to Cu₃${}_3$N changed the film an electrical conductor. Films of AlN and TiN were rather insensitive to the hydrogen introduction; the hydrogen effect was only observed when the nitrides contain some imperfection in the compounds.     

Temperature effect on the electrical properties of undoped NiO thin films

Undoped NiO thin films have been prepared onto glass substrate by e-beam evaporation of the element Ni in vacuum at 2 × 10⁻⁴ Pa. The as-deposited Ni films were then oxidized in air by heating about 2 h at a temperature of 470 K and then the oxidized Ni films are turned into NiO thin films. From the deposition time and film thickness after annealing in air, an effective deposition rate of NiO thin films was about 6.67 nms⁻¹. X-ray diffraction (XRD) study shows the NiO films are amorphous in nature. SEM studies of the surface morphology of NiO films exhibit a smooth and homogeneous growth on the entire surface. The elemental composition of NiO films is estimated by Energy Dispersive Analysis of X-rays (EDAX) method. The effects of temperature on the electrical properties of NiO thin films were studied in details. The heating and cooling cycles of the samples are reversible in the investigated temperature range after successive heat-treatment in air. Thickness dependence of conductivity is well in conformity with the Fuchs–Sondheimer theory. Temperature dependence of electrical conductivity shows a semiconducting behavior with activation energy. The thickness dependence of activation energy as well as thermopower studies was done within 293–473 K temperature range, respectively. Thermopower study indicates the NiO films a p-type semiconductor. Optical study in the wavelength range 0.3 < λ<1.2 μm range exhibits a high transmittance in the visible as well as in the near infra-red. Calculation from the optical data, the NiO sample exhibits a band gap at 3.11 eV, which does agree well with earlier reported values. These studies may be of importance for the application of this material in energy efficient surface coating devices.     

The impact of etching during microfabrication on the microstructure and the electrical conductivity of gadolinia-doped ceria thin films

Gadolinia-doped ceria, Ce_0.8Gd_0.2O_1.9−x (CGO), thin films deposited by spray pyrolysis and annealed to different degree of crystallinity between 0% and 95% are exposed to different etchants and etching methods. The attack of the etchants on the CGO thin films is analyzed with respect to changes in microstructure and in-plane electrical conductivity. It is found that amorphous CGO films are dissolved in hydrochloric acid after elongated etching times. Hydrofluoric acid severely attacks CGO thin films after already short times of exposure (1 min), more intense the less crystalline the thin film is. Ar ion etching smoothens the surface of the CGO thin films without considerable removal of material. No microstructural attack of NaOH, CHF₃/O₂ and SF₆/Ar is found. The electrical conductivity is in general only affected when microstructural changes are severe. Therefore, it is concluded that CGO thin films can be well used as functional layers in micro-fabricated devices and that micro-fabrication is, with the exception of hydrofluoric, not harmful for the electrical properties of crystalline CGO thin films.     

The effect of sorbitol on the morphological characteristics of lead–tin films electrodeposited from an alkaline bath

An alkaline Pb–Sn plating bath containing sorbitol as additive has been developed, which has the advantage of low toxicity and ease of handling relative to fluoborate baths, etc. The Pb–Sn deposition voltammetric curve from this bath revealed two deposition processes, at −0.87 and −1.17 V. The voltammetric studies at various sweep rates indicate that the Pb–Sn deposition process is controlled by mass transport. The joint diffusion coefficient of the Pb(II) and Sn(II) sorbitate complex species is 1.15 × 10⁻⁶ cm² s⁻¹. SEM analysis showed that the films produced at −0.87 and −1.17 V are, respectively, composed of dendritic or hexagonal crystals, showing that co-deposition of tin hindered dendritic growth. EDS of the Pb–Sn films showed that the deposit obtained at −0.87 V is pure lead, while that at −1.17 V, with 5.0 or 10.0 C cm⁻², has 19.10 wt% Sn or 26.35 wt% Sn, respectively. It was observed that the Pb–Sn electrodeposited films were grey at both deposition potentials (−0.87 and −1.17 V) and deposition charges (5.0 and 10.0 C cm⁻²). X-ray spectra showed that at the potential −0.87 V a mixture of Pb, PbPt₄ and Pb₂PtO₄ were deposited, while at −1.17 V, Pb, β-Sn, and PbSnO₃ were deposited.