Recent developments on transparent insulation materials and light switching devices for passive solar energy usage

This paper gives an overview on new developments in the field of transparent insulation (TI) materials and systems. Monolithic or granular SiO₂-aerogels, PMMA, polycarbonate or glass capillaries as well as light switching layers are discussed.Monolithic aerogels prepared under basic conditions show only weak Rayleigh- scattering resulting in high transmittance values. Thus a solar averaged hemispherical transmission of for 20 mm thick specimens is achieved. In the visible spectral region directional-directional transmittance values ranging up to 90 % are measured. Beside the granular waterglass derived SiO2-aerogels produced by BASF also the lightscattering properties of newly developed aerogel pellets using TMOS as precursor are investigated. In comparison with both aerogel types the thermal and optical properties of capillary structures are discussed.A newly developed thermochromic gel layer allows to switch the solar input from 85 % down to 10 % via radiation backscattering. To achieve this transmission reduction a gel thickness of only 1 mm is necessary. With an optimized polymer dispersed liquid crystal system a transmission reduction of 30 % is also obtained solely by scattering. The electrical power necessary to maintain the transparent state was reduced to a value of 5 W/m² by decreasing the frequency of the applied ac-voltage. An electrochronic switching levice exhibits a switching level of 40 % ensuring a high visual image transmission by changing the absorption coefficients mainly in the red and near infrared spectral region.     

Comparative study of transparent insulation materials cover systems for integrated-collector-storage solar water heaters

The thermal performance of transparently insulated integrated-collector-storage solar water heaters is investigated theoretically as well as experimentally for a comparative study of cover systems having transparent insulation materials devices placed between the top glazing and the absorber. The data on solar transmittance, heat loss reduction characteristics and solar collector-storage efficiencies of various configurations is generated for the system performance comparisons. These hot water systems exhibit average (diurnal basis) solar collection and storage efficiencies in the range of 20–40% at a collection temperature of 40–50°C. The performance of water heaters with cover system having absorber-perpendicular configuration of TIM excel over absorber-parallel TIM covers. The effect of variation in the temperature of heat collected and cost of cover systems on the performance comparisons is also discussed.     

Transmittance-absorptance product of solar glazing with transparent insulation materials

The transmittance-absorptance product of solar glazing containing the transparent insulation material (TIM) of square celled honeycomb is investigated. A method is developed for the determination of transmittance-absorptance product of beam, sky and ground diffuse solar radiations using the individual transmittances of cellular array and encapsulating covers; the internal reflections are taken into account. Three practical cases; cellular array, cellular array with top cover, and cellular array with top and bottom covers are considered. The results are presented for beam radiation as a function of angle of incidence and sky and ground diffuse radiation as a function of tilt angle. The predicted results are tested by measuring the global radiation transmittance of commercial TIM; the predicted results deviate from the measurements by an average of 2.0%.     

A review of transparent insulation systems and the evaluation of payback period for building applications

Research and development of transparent insulation systems (TI-systems) has been ongoing for 20 years with transparent insulation materials (TIMs) used to replace standard opaque insulation materials. TIM not only performs similar functions to opaque insulation, reducing heat losses and controlling indoor temperatures, but allows solar transmittance of more than 50%. With a thickness of less than 20 cm, it can provide a financial return to building occupants when applied to building facades, maximising occupiable and sellable spaces in urban areas, without compromising thermal comfort within buildings.In this review of TI-systems for building applications, drawbacks to previous applications, cost trends, and analysis of the limitation in information from previous studies are discussed. A major drawback in the development of TI-systems identified is the lack of cost information; the payback periods for TI-systems used in previous renovation projects are virtually unknown. Simple payback period calculations were undertaken based on information available from a demonstration project documented by the Solar Heating and Cooling (SHC) Programme of the International Energy Agency (IEA) Task 20 “Solar Energy in Building Renovation”. The calculations indicated an encouraging 5–8-year payback period for this particular case study. It was concluded that the simple payback period calculation may be used for feasibility studies to indicate the time required to recoup investment when installing TI-systems and to provide initial guidance for building designers when evaluating the potential application of TI-systems in their buildings.     

我国生物质作为建筑保温材料的潜力分析

叙述了生物质材料在我国的应用现状及存在的问题,综合分析生物质材料的应用潜力,提出将生物质材料应用于建筑保温材料的可行性,结合目前国内的技术提出一些建设性的意见。     

The use of transparent insulation in low energy dwellings in cold climates

This article discusses the use of transparent insulation materials in low energy dwellings in cold climates. Both aesthetic and thermal issues for the capillary type of transparent insulation material are investigated. In Lien (1995) granulated silica aerogel and multilayered material of corrugated sheets are also presented.To investigate the aesthetic qualities of the material, a scale model study is performed. The study treats the distribution of daylight, the visual contact through the materials, and the appearance of the materials. The results show, among other things, that the capillary material spreads direct daylight in a cone shape and distributes it to certain areas of the floor, walls, and ceiling of a room. The visual contact through the materials is limited and dependent on the thickness of the material, the illumination situation, the distance between the observer and the material and the object observed, and the angle of direction at which the observer looks through the material.Calculations of the energy consumption for heating and ventilation are performed for a row house with different sizes of materials. The calculations are done for two climate zones in Norway. The results show that energy savings in the order of 20% can be attained. The results are especially promising for the coldest climate zone, where the problem of overheating is small and the energy saving potential is still good.     

Variation of discomfort with south window area and insulation on walls/roof

Dependence of the discomfort index on the south window area and the cost of optimally distributed insulation over the walls and roof (corresponding to different available investments) of a non-air-conditioned one room building is investigated. It is assumed that, in the winter, the wooden shutters provided in the window are opened during the day and are closed during the night, and that, in the summer, the shutters are closed during the day and are opened during the night. It is seen that the discomfort decreases with increasing window area and an increasing amount of insulation.     

Structure–property correlations of polymeric films for transparent insulation wall applications. Part 1: Solar optical properties

In this paper the results of a research project to establish a fundamental understanding of the physical relationships between the material structure and solar optical properties of polymeric transparent insulation (TI) materials are described. First, a systematic characterization of potential materials for TI applications in respect to their relevant physical properties in the solar radiation range was done. Second, based on the investigation of polymer films with different thicknesses model functions for the solar optical properties were established. Third, the solar optical properties were interpreted on base of polymerphysical relations. The characterization in the solar range and the calculation of solar optical film properties have shown, that the solar extinction is dominated by scattering occurring mainly at the surface. A linear relationship between the solar optical thickness and the film thickness was obtained for film thicknesses ranging from 12 to 150 μm. For various amorphous and semi-crystalline films the surface roughness correlated well with the solar optical thickness.     

Structure–property correlations of polymeric films for transparent insulation wall applications. Part 2: Infrared optical properties

In this paper the results of a research project to establish a fundamental understanding of the physical relationships between the material structure and the infrared optical properties of polymeric transparent insulation (TI) materials are described. First, a systematic characterization of potential materials for TI applications in respect to their relevant physical properties in the infrared radiation range was done. Second, based on the investigation of polymer films with different thicknesses model functions for the infrared optical properties were established. Third, the infrared optical properties were interpreted on base of polymerphysical relations. The characterization in the infrared range and the calculation of infrared optical film properties have revealed, that various functional groups of the macromolecular structure are highly absorbing. For polymers with service temperatures of about 100 °C the carbon–oxygen single bond was identified as highly effective. For 50 μm thick films a good correlation between the concentration of the functional carbon–oxygen group and the non-spectral infrared optical thickness as well as the hemispherical emittance was found. An outstanding performance profile for TI wall applications with black absorbers was obtained for cellulose based materials.     

Finite time thermal analysis of ground integrated‐collector‐storage solar water heater with transparent insulation cover

A transparent honeycomb insulated ground integrated‐collector‐storage system has been investigated for the engineering design and solar thermal performance. The system consists of a network of pipes embedded in a concrete slab whose surface is blackened and covered with transparent insulation materials (TIM) and the bottom is insulated by the ground. Heat may be retrieved by the flow of fluid through the pipe. A simulation model has been developed; it involves the solution of the two‐dimensional transient heat conduction equation using an explicit finite‐difference scheme. Computational results have been used to determine the effect of such governing parameters as depth as well as pitch of the pipe network and collector material on the thermal performance of the system. The pipe network depth of 10 cm and the TIM cover made of 5 cm compounded honeycomb seem suitable for the proposed system. Solar gain (solar collection efficiency of 30–50% corresponding to collection temperature of 40–60°C) and the diurnal heat storage characteristics of the system are found to be of the right order of magnitude for solar water heating applications. Copyright © 1999 John Wiley & Sons, Ltd.     

Application demonstration and performance of a cellulose triacetate polymer film based transparent insulation wall heating system

For the application demonstration of cellulose triacetate (CTA) polymer film based transparent insulation (TI) structures a technically and ecologically optimized TI facade system was developed and used to equip a south-oriented wall of a solar house meeting passive house standard in Graz, Austria. The demonstration building was equipped with an appropriate data recording system for solar irradiation, temperature, heat flux and humidity. The practical experiences within the heating periods 2002/03 and 2003/04 are reported in this paper. For the optimized TI facade system a solar energy efficiency of about 43% and a U-value of 0.76 W/(m² K) were obtained. Although CTA absorbs a high amount of water no adverse condensation phenomena were observable visually. The reasoning for these findings is explained and related to construction details.     

The research applications of new heat insulation composite material in automobiles

With the rapid development of its unique advantages, nonwoven fabric has become the leading material of automotive textiles. Nonwoven fabric has become an ideal material for automobiles and replaced traditional textiles and plastic products. This paper takes a car as the research model. A DRL‐2B thermal conductivity tester was used to test thermal conductivity of the material based on the plate method. Material systems and structures of new types of heat insulation composite materials were determined according to test results and the theory of heat transfer. Then, the final new type of heat insulation material was determined by calculating and comparing average heat transfer coefficients and heat transfer between traditional insulation materials and new types of heat insulation materials. The calculated results were verified by experiments in this paper. All the test results show that the new type of composite insulation material is significantly better than traditional insulation materials, and the test results match the calculated results.     

U-values, optical and thermal coefficients of composite glass systems

This paper presents a different approach for thermal effective windows, i.e. windows which reduce energy transmitted into or out of the room. The idea is to use a double-sealed glass filled with pcm whose fusion temperature is determined by solar-thermal calculations. The investigation is divided into two main parts: modeling of the heat and radiation transfer through the composite window and the optical investigation of the pcm-filled window. A one-dimensional thermal model for the composite window was developed to predict the resulting effects due to variation of the geometrical and pcm thermal properties. Optical investigations using photo-spectrometry were realized on single glass, double glass filled with air, and double glass filled with pcm. The transmittance and reflectivity tests indicate large reductions in the infrared and ultraviolet radiations while maintaining the good visibility. The effects of thickness of glass and spacing were also analyzed.     

Performance and economic analysis of air flow windows in a tropical climate

An experimental study was conducted in Thailand to determine the thermal performance of twin glazed windows with dynamic insulation. The effects of blinds situated either between or outside the glazing were analysed. With an external blind, the heat transfer coefficient was 1–25 W/m²°C with natural convection and 0–6 W/m²°C for a flow of 20m³/h (glass area = 2–16m²). The solar flux transmitted was evaluated analytically and experimentally depending on the blind's position. An economic study was performed on a six-sotrey air-conditioned building in Thailand. It showed in tropical countries that it may be more economical to use air flow windows than to have tinted single or double glass windows.     

The use of double-sided cloth without diffusion layers as air-cathode in microbial fuel cells

The cost of electrode materials is one of the most important factors limiting the scale of microbial fuel cells (MFCs). In this study, a novel double-sided cloth (DC) without diffusion layer is using as air-cathode, which decreases the cost and simplifies electrode production process. Using Pt as catalyst, the maximum power density of MFC using DC cathode is 0.70 ± 0.02 W m⁻², which is similar to that obtained using carbon cloth (CC) cathodes (0.66 ± 0.01 W m⁻²). After running in stable status, the Coulombic efficiencies (CEs) (18 ± 1%) and COD removal rates (75 ± 3%) are almost the same as those of CC cathode with diffusion layers. Using carbon powder as catalyst on the DC cathode, the maximum powder density is 0.41 ± 0.01 W m⁻², with a COD removal rate of 66 ± 2% and a CE of 13.9 ± 0.5%. The total cost of cathode based on power output decreases as follows: CC with Pt (CC-Pt, 2652$ W⁻¹), DC with Pt (DC-Pt, 1007$ W⁻¹) and DC with carbon powder (DC-C, 22$ W⁻¹), showing that DC is an inexpensive and promising cathode material for future applications.     

Adjustable insulation for enhancing the performance of phase change materials in buildings

The energy savings of a building roof integrated with a phase change material (PCM) and different insulation strategies are presented in this paper. The proposed roof structure includes a concrete slab with a PCM layer and an air cavity insulation, which can be adjusted according to certain strategies. The adjustable insulation is devised to enable a reduced total heat gain throughout 24 h in summer days, thereby improving the performance of the PCM. The heat gain/loss through the roof with the PCM layer and adjustable insulation is compared with that of the roof with the PCM layer and fixed insulation during a typical year in Hangzhou, China. The effects and optimization of the melting temperature of the PCM are also explored. The simulation results show that, overall, the adjustable insulation can reduce the daily heat flux through the roof by approximately 20% compared with the conventional fixed insulation.     

The application of dynamic insulation in buildings

Dynamic insulation, a form of ‘Breathing Wall’ construction which allows the movement of air and moisture through the external walls of a building, was seen as one possible method for reducing building envelope heat losses and achieving high indoor air quality. A research investigation was conducted to provide a firm scientific understanding of dynamic insulation. An important outcome of the work will be the development of building envelope designs which effectively and economically employ dynamic insulation in cold climates. This paper presents some general conclusions, confirming that the energy saving produced by dynamic insulation alone is small relative to that obtained in conjunction with conventional air heat recovery methods.     

工业炉热风管道的热经济保温层厚度

从寿命经济学观点出发,讨论了工业炉热风管道最佳保温层厚度的问题。结果表明,保温层厚度的确定不仅取决于保温材料的费用,而且取决于换热器的投资费用。     

Structural and optical properties of electrodeposited CuInSe2 layers

CuInSe₂ thin layers have been obtained from a thiocyanate electrolyte with a complexing agent. The as-deposited layers have been polycrystalline with very small crystallites. The influence of the deposition potential on the composition, on the absorption coefficient, and on gap band energy has been investigated. It has been established that the layers were Cu-rich and crystallized in chalcopyrite phase. The annealing in Ar ambient did not influence the composition of the layers considerably but improved the crystalline structure. This resulted in changes of the absorption coefficient and bandgap energy.     

玻璃用透明隔热水性纳米涂料研究进展

玻璃用透明隔热水性纳米涂料因其环保、节能和良好的视觉效果而日益受到研究者和相关产业界重视,但存在现场施工不便,隔热性能欠缺、涂层耐水性不佳等问题。简要介绍了二氧化锡锑基透明隔热涂料的研究进展和产业化状况,着重介绍了隔热机理、实际应用中存在的问题以及可能的解决办法。