Evacuated aerogel glazings

This paper describes the main characteristics of monolithic silica aerogel and its application in evacuated superinsulating aerogel glazing including the evacuation and assembling process. Furthermore, the energetic benefit of aerogel glazing is quantified. In evacuated aerogel glazing the space between the glass panes is filled with monolithic silica aerogel evacuated to a rough vacuum of approximately 1-10 hPa. The aerogel glazing does not depend on use of low emissive coatings that have the drawback of absorbing a relatively large part of the solar radiation that otherwise could reduce the space heating demand in residential buildings. The U-value of the glazing can be designed to meet the required value by increasing the monolithic silica aerogel thickness without the need for additional layers of glass. An aerogel glazing with 20 mm glass distance can reach a U-value below 0.5 W/(m² K) combined with a solar energy transmittance above 0.75.     

Vacuum glazing: Current performance and future prospects

The development of vacuum glazing is a significant advance in the area of low heat loss glazing systems with great potential to reduce building heating and when combined with solar control glazing, cooling loads. The basic concept of vacuum glazing is reviewed and the procedures and research undertaken in the development of both high-temperature and low-temperature sealing of vacuum glazing are outlined. The achieved thermal performance of current laboratory systems and those that are now commercially available are presented. The potential levels of performance that may be achieved using high-performance low-emittance (low-e) coatings and tempered glass are reported. Research into window systems that incorporate vacuum glazing to achieve improved thermal performance is also outlined.     

Heat Transport and Thermal Expansion of Electrochromic Glazing Systems Due to Solar Irradiation

For many technical and architectural applications of electrochromic glazings a thorough understanding of the heat transport and the optical and thermal radiative properties of the system is essential. Furthermore, the thermal expansion and eventually the induced stresses within the laminated system are of interest. To meet these demands the solar absorptance of the electrochromic glazings at different tinted states were measured using an UV–VIS-NIR spectrometer. The thermal expansion coefficients of the glass materials were determined by a push-rod dilatometer. Then the instationary coupled conductive and radiative heat transfer due to solar irradiation were calculated for various pane configurations by finite element analysis. Starting from the resulting instationary temperature fields, the stress and strain states within the laminated glazing system were calculated.     

大厚度差真空玻璃隔声特性研究

Cabrera和Nugroho等人对3v3(3 mm单层玻璃+0.2 mm真空层+3 mm单层玻璃)、3v5以及5v5构造的真空玻璃进行了研究,结果表明真空玻璃的隔声特性符合薄板隔声理论,但10 mm单层玻璃较符合厚板隔声理论。因此需进一步研究当真空玻璃的厚度进一步增大后的隔声特性。文章增加真空玻璃厚度至3v10,采用现场声强测量法进行隔声测量,基于Davy和Sharp隔声理论建立了隔声模拟模型,对实测和模拟特性进行对比分析。结果表明,3v10真空玻璃的隔声特性更符合厚板隔声理论。与3v5真空玻璃相比,3v10真空玻璃的计权修正表观隔声量未明显提高,但有助于降低现场隔声等级隔声最低值与评价量之间的差值。     

Influence of Spacer Systems on Heat Transfer in Evacuated Glazing

One attractive possibility to essentially improve the insulation properties of glazing is to evacuate the space between the glass panes. This eliminates heat transport due to convection between the glass panes and suppresses the thermal conductivity of the remaining low pressure filling gas atmosphere. The glass panes can be prevented from collapsing by using a matrix of spacers. These spacers, however, increase heat transfer between the glass panes. To quantify this effect, heat transfer through samples of evacuated glazing was experimentally determined. The samples were prepared with different kinds of spacer materials and spacer distances. The measurements were performed with a guarded hot-plate apparatus under steady-state conditions and at room temperature. The measuring chamber of the guarded hot plate was evacuated to < 10⁻² Pa. An external pressure load of 0.1 MPa was applied on the samples to ensure realistic system conditions. Radiative heat transfer was significantly reduced by preparing the samples with a low-ε coating on one of the glass panes. In a first step, measurements without any spacers allowed quantification of the amount of radiative heat transfer. With these data, the measurements with spacers could be corrected to separate the effect of the spacers on thermal heat transfer. The influence of the thermal conductivity of the spacer material, as well as the distance between the spacers and the spacer geometry, was experimentally investigated and showed good agreement with simulation results. For mechanically stable matrices with cylindrical spacers, experimental thermal conductance values ≤0.44W·m⁻² ·K⁻¹ were found. This shows that U _g -values of about 0.5W · m⁻² · K⁻¹ are achievable in evacuated glazing, if highly efficient low-emissivity coatings are used.     

Selectively coated high efficiency glazing for solar-thermal flat-plate collectors

In order to increase the efficiency of solar-thermal flat-plate collectors at temperatures above 100 °C or with low solar irradiation, we implement a double glazing with a low-emitting (low-e) coating on the inner pane to improve the insulation of the transparent cover. Since commercially available low-e glazing provides only insufficient solar transmittance for the application in thermal flat-plate collectors we are developing a sputter-deposited low e-coating system based on transparent conductive oxides which provides a high solar transmittance of 85% due to additional antireflective coatings and the use of low-iron glass substrates. Durability tests of the developed coating system show that our low e-coating system is well suitable even at high temperatures, humidity and condensation.     

Thermal stress fracture of solar control window panes caused by shading of incident radiation

The phenomenon of thermal stress fracture in solar control window panes in high-rise buildings due to shading of incident radiation is investigated in this paper. An experimental method, in which a bank of infra-red lamps was used as the simulated solar source, was developed to measure thermal strains and hence thermal stresses built up at the cool edges of the glass pane which was glazed in a480 mm square aluminium frame. Horizontal and diagonal shadows both increased the thermal stresses by approximately10% when compared with the unshaded glass panes. It is shown that fracture mechanics can be used to analyse and predict fracture stresses once the mirror radius and the fracture toughness of the glass pane are known. These predictions agree very well with experimental measurements. Finally, a new glazing technique using a thermal conducting sealant in the rebate is suggested to minimise the incidence and risk of thermal stress fracture. This is achieved by raising the temperature of the cool edges and thus lowering the differential heating effect. Preliminary experiments show that the method is promising.     

CPC热管真空管式热水器实验研究

研制了一种CPC(复合抛物面聚焦)热管真空管式太阳能热水器。该热水器在普通玻璃真空管热水器的基础上耦合热管技术,并增加了CPC聚光板。对该热水器与全玻璃真空管太阳能热水器进行了热性能对比实验研究。结果表明,在300 W/m2~800 W/m2日照条件下,该新型热水器单位面积集热功率最高可达610 W/m2;平均集热效率约为80%,比全玻璃真空管太阳能热水器的瞬时效率高10%~20%;导热介质的最高温度达到103℃。证明增加CPC聚光板及运用导热油可有效提高集热品位,利用热管技术可解决严寒地区的抗冻问题,所以,CPC热管真空管式太阳能热水器将具有较广阔的市场前景。     

A year-round dynamic simulation of a solar-driven ejector refrigeration system with iso-butane as a refrigerant

In this paper, the performance of the solar-driven ejector refrigeration system with iso-butane (R600a) as the refrigerant is studied. The effects that both the operating conditions and the solar collector types have on the system's performance are also examined by dynamic simulation. The TRNSYS and EES simulation tools are used to model and analyze the performance of a solar-driven ejector refrigeration system. The whole system is modelled under the TRNSYS environment, but the model of the ejector refrigeration subsystem is developed in the Engineering Equations Solver (EES) program. A solar fraction of 75% is obtained when using the evacuated tube solar collector. In the very hot environment, the system requires relatively high generator temperature, thus a flat plate solar collector is not economically competitive because the high amount of auxiliary heat needed to boost up the generator temperature. The results from the simulation indicate that an efficient ejector system can only work in a region with decent solar radiation and where a sufficiently low condenser temperature can be kept. The average yearly system thermal ratio (STR) is about 0.22, the COP of the cooling subsystem is about 0.48, and the solar collector efficiency is about 0.47 at T_e 15 °C, T_c 5 °C above the ambient temperature, evacuated collector area 50 m² and hot storage tank volume 2 m³.     

Elektrochrome Beschichtungen

Electrochromic Coatings – Solar Control Glazing of a New Generation Since the early sixties of the 20th century the permanent expanded quantities and qualitative requirements for coatings on architectural glass have pushed the development of the processing technology. Today the magnetron‐sputter technology is the standard for coating of broadsheet architectural‐ and car glass. It provides a huge range of variation in case of processing parameters and it is therefore best suited to realize the next generation of architectural glazing based on electrochromic coatings. The history and background information's to the requirements of coating technology will be discussed. Finally there are two examples for switchable solar control glazing in a building.     

Preparation of a transparent supporting spacer array for vacuum glazing

Materials used to produce spacers present in vacuum glazing have classically been opaque. The present study suggests a method to produce transparent spacers, which allows for the production of novel nearly transparent vacuum glazing. The transparent glass spacer array between two sheets of glass substrates was prepared by screen printing. A typical paste composition with suitable screen-printing behaviors is evaluated in weight percent: 24 Wt% organic vehicle, and 76 Wt% low melting glass powder. The paste is a shear thinning and has a viscous liquid behavior dispersion system with little thixotropy. This novel method to prepare a transparent spacer array for vacuum glazing is reliable and superior to the commonly used metal pillar array in terms of appearance, transmittance, Vickers hardness, and the thickness uniformity of the prepared spacers.     

Zugkraft‐Lastenträger für Vakuumisolation

Tension Carrier and spacer for Vacuum Insulation and general mechanics (and heat brige free usage) A life long dream of researchers and developers of spacers for supported vacuum arrangements cam true and an easy to manufacture elementary Tension Carrier is now developed. It makes it possible, to carry the forces produced by pressure difference by elements, which are bearing tension forces only. Through that conductive heat transfer rates up to 1E‐6 W/mK and lower are attainable. The new Tension Carriers allow further an easy accomodation of unloaded radiation rejection means in evacuated room. Moreover this Tension Carriers have improved abilitys for faster evacuation and have great reserves for constructive and material adaptation in applications. Especially heat bridge free evacuated system embodiments will be achievable, but also sealed VIP‐Plates benefit from attainable improvement in performance and costcutting.     

电色smart窗

综述了电色smart窗的由来、设计准则、窗的基本结构。介绍了组成窗的各层膜特性，某些试制型窗的实例、还探讨了电色开关窗器件的耐久性问题。     

高性能SS-AlN金属陶瓷真空太阳集热管的制备

采用真空磁控溅射沉积SS-AlN金属陶瓷太阳选择性吸收涂层.涂层光学功能层的制备,先采用铜靶溅射Cu红外反射层;再采用不锈钢(SS)和铝两金属靶在Ar和N2的混合气体中同时溅射沉积SS-AlN金属陶瓷吸收层;最后采用Al靶在Ar和N2中反应溅射沉积AlN减反射层.金属陶瓷吸收层由高、低SS体积份额的两吸收子层组成.优化溅射镀膜工艺参数获得高性能吸收涂层,太阳吸收比α(AM1.5)高达0.956±0.003(国标GB:α≥0.86),比GB高10％;红外发射比ε仅为0.043±0.003(GB:ε≤0.08).制备成φ58×2100 mm全玻璃真空太阳集热管,80℃平均热损系数ULT仅为0.47±0.01 W/m2℃ (GB:ULT≤0.85 W/m2℃),比GB低0.38W/m2℃,性能提高45％.制备的真空集热管具有良好的真空品质,集热管内管加热350℃恒温480 h后,吸气镜面轴向长度平均消失率仅为2～3％,集热管真空品质优于GB高达100倍以上(GB:350℃恒温48 h,镜面消失率≤50％).     

Switchable windows with tungsten oxide

Tungsten oxide can change its colour reversibly upon electron injection. It can be produced by sputtering, evaporation, chemical vapour deposition or other processes. In addition to its high colouration efficiency and fast reaction kinetics, the redox potential of the electron injection is low enough to allow various switchable systems, such as electrochromic, gasochromic, photoelectrochromic or photochromic glazing. In this paper, electrochromic devices with a redox electrolyte are introduced. This is related to the photoelectrochromic device, which is an electrochromic device with redox electrolyte and an additional dye-sensitised layer of TiO₂, which generates the energy for the colouration of the device by sunlight. The photochromic device is in principal a photoelectrochromic device, where the catalytic layer for the reaction of the redox electrolyte is in direct contact with the electrochromic layer. In gasochromic devices, tungsten oxide reacts with diluted hydrogen and oxygen gases. This paper aims to give an overview of these different approaches.     

Vacuum insulation panels—From research to market

Vacuum insulation panels (VIPs) have a thermal resistance about a factor of 10 higher than that of equally thick conventional polystyrene boards. Similar to thermos flasks these systems make use of ‘vacuum’ to suppress the heat transfer via gaseous conduction. While thermos flasks are to be pumped down to a high vacuum, filling material integrated in the flat VIP elements, which bears the atmospheric pressure load, reduces the requirements on the vacuum and thus on the tightness of the vacuum casing. Optimal in this respect is a kernel of fumed silica. This kernel is evacuated to below 1 mbar and sealed in a high-barrier laminate, which consists of several layers of Al-coated polyethylene (PE) and polyethylene terephthalate (PET). The laminate is optimized for low air and moisture leakage rates and thus for a long service life. The evacuated silica kernel has a thermal conductivity of about 0.004 W m⁻¹ K⁻¹ at room temperature, mainly resulting from solid thermal conduction along the tenuous silica backbone. As the kernel is nanoporous, the gaseous thermal conductivity becomes noticeable only for pressures above 10 mbar. At about 200 mbar the thermal conductivity measures about 0.008 W m⁻¹ K⁻¹. Such a gas pressure could occur after several decades of usage in a middle European climate. With VIP, slim yet highly insulating façade constructions can be realized. A centre U-value of 0.2 W m⁻² K⁻¹ can be achieved for a VIP thickness of only 2 cm, if optimized kernels and barrier laminates as well as stringent quality control are employed. A successful “self-trial” using VIPs within a façade of the ZAE-building in Würzburg in 1999 was the starting point for new applications of evacuated insulations in the building sector.     

Multi-scale Modeling of Radiation Heat Transfer through Nanoporous Superinsulating Materials

In this contribution, the extraordinarily high level of thermal insulation produced by nanoporous materials, which can achieve thermal conductivities down to a few mW·m⁻¹·K⁻¹ when they are evacuated to a primary vacuum, is highlighted. The objective here is to quantify the level of radiation heat transfer traveling through a nanoporous material in relation with its composition. The model used here is based on the “non-gray anisotropically scattering Rosseland approximation,” which allows the definition of a “radiation thermal conductivity” expressed as a function of the optical properties (complex optical index spectra), mean sizes and volume fractions of the different populations of particles constituting the material. With the help of this simple model, one can draw interesting conclusions concerning the impacts of different parameters related to the microstructure of the nanoporous material on the amplitude of the radiation heat transfer. In the future, this model should help to orient the formulation of new nanoporous materials with optimized radiative properties. Paper presented at the Seventeenth European Conference on Thermophysical Properties, September 5–8, 2005, Bratislava, Slovak Republic.     

真空玻璃边缘封接强度及可靠性分析

用于真空玻璃边部封接的玻璃焊料不仅要满足真空密封性能,同时应满足封接强度要求。采用十字交叉法试验,获得了真空玻璃边缘封接部位界面拉伸与剪切强度,分析了真空玻璃服役过程中因玻璃自重、风载荷和温差作用而导致的真空玻璃边缘封接部位应力。通过试验验证和理论分析比较,结果表明:真空玻璃边缘封接部位强度能够承受因玻璃自重,温差,风压作用而产生的应力;在真空度失效的情况下,真空玻璃边缘封接强度足够高,依然可以承受3600Pa的风压作用,在应用过程中安全可靠。     

Control of radiation heat transfer through a composite window featuring ER fluid: A conceptual investigation

Radiation heat transfer control through the application of an electric field upon an Electroheological (ER) fluid based composite material is an innovative new area of research. A conceptual experiment has been conducted to study radiation heat transfer through a composite window featuring an ER fluid. The composite window is composed of two thin glass plates with a layer of ER fluid contained between them. The glass walls were transparent except for a very thin coating of an electric-conductive film which enabled the inside of the glass surfaces to serve as electrodes. The ER fluid was contained between the glass surfaces and consisted of a suspension of micron sized crystalline zeolite particles in a silicon oil. This study has demonstrated the unique capability of ER fluids to regulate and control radiation heat transfer via transmittance measurements. A semi-empirical model is developed from the experimental data to correlate the dependence of radiation transmission through ER fluids based on several physical parameters (f_v, V^*, and L). This model agrees reasonably well with the measured data. The results obtained in this study are very important to those concerned with the development of a thermally smart material for heat transfer control.Presented at the Second Minsk International Heat and Mass Transfer Forum, May 18–22, 1992.     

The use of aluminium doped ZnO as transparent conductive oxide for CdS/CdTe solar cells

CdTe/CdS and CdTe/ZnO thin film solar cells were grown with a high vacuum evaporation based low temperature process (≤ 420 °C). Aluminium doped zinc oxide (AZO) was used as transparent conducting oxide (TCO) material. AZO exhibited excellent stability during the solar cell processing, and no significant change in electrical conductivity or transparency was observed. The current density loss due to absorption in the 1 μm thick AZO layer with 5 Ω per square sheet resistance was found to be 1.2 mA/cm². We investigated the influence of an intrinsic ZnO layer (i:ZnO) in combination with various CdS thicknesses. The i:ZnO layer was found to significantly increase the open circuit voltage of the solar cells with very thin CdS layer. Increasing thickness of the i:ZnO layer leads to UV absorption losses, narrowing of the depletion layer width and hence reduced collection efficiency in the long wavelength (685-830 nm) part. With AZO/i:ZnO bi-layer TCO we could achieve cell efficiencies of 15.6% on glass and 12.4% on the flexible polyimide film.