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In today's society there is an increased focus on various energy aspects. Buildings constitute a large part of the total energy consumption in the world. In this respect it is important to have the optimum heat balance in building...
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In today's society there is an increased focus on various energy aspects. Buildings constitute a large part of the total energy consumption in the world. In this respect it is important to have the optimum heat balance in buildings. That is, in a cold climate one wants to have as well thermally insulated building envelopes as possible. However, even in cold climates there might often be relatively long periods of overheating in the buildings, for example, due to solar heat gains and excessive heat loads from miscellaneous indoor activities. In warm climates overheating is most often the case, for example, in office work spaces with large window glass facades and extensive use of electrical equipment. Insulation retrofit is among the most cost-effective measures, even more cost-effective than, for example, solar photovoltaics. The traditional thermal insulation materials of today have typically thermal conductivities between 33 and 40 mW/(mK). State-of-the-art thermal insulation includes vacuum insulation panels (VIPs) with conductivities between 3 and 4 mW/(mK) in fresh condition to typically 8 mW/(mK) after 25 years aging due to water vapor and air diffusion into the VIP core material, which has an open pore structure. Puncturing the VIP envelope causes an increase in the thermal conductivity to about 20 mW/(mK). The main emphasis of this work centers around the possibilities of inventing and developing innovative and robust highly thermal insulating materials. That is, within this work the objective is to go beyond VIPs and other current state-of-the-art technologies. New concepts are introduced, that is, advanced insulation materials (AIMs) as vacuum insulation materials (VIMs), gas insulation materials (GIMs), nano insulation materials (NIMs), and dynamic insulation materials (DIMs). These materials may have closed pore structures (VIMs and GIMs) or either open or closed pore structures (NIMs). The DIMs aim at controlling the material insulation properties, that is, solid state thermal conductivity, emissivity, and pore gas content. Fundamental theoretical studies aimed at developing an understanding of the basics of thermal conductance in solid state matter at an elementary and atomic level have been addressed. The ultimate goal of these studies is to develop tailor-made novel high performance thermal insulation materials and dynamic insulation materials, the latter one enabling to control and regulate the thermal conductivity in the materials themselves, that is from highly insulating to highly conducting. Furthermore, requirements of the future high performance thermal insulation materials and solutions have been proposed. At the moment, the NIM solution seems to represent the best high performance low conductivity thermal solution for the foreseeable future. If robust and practical DIMs can be manufactured, they have great potential due to their thermal insulation regulating abilities.
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Despite the extensive investigations carried out on the pollution performance of outdoor insulators, the flashover characteristic and its interaction with insulator shape is still not very well understood. In this paper, we presen...
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Despite the extensive investigations carried out on the pollution performance of outdoor insulators, the flashover characteristic and its interaction with insulator shape is still not very well understood. In this paper, we present findings of experiments which allow quantifying the effects of insulator geometry on the flashover voltage. Two main parameters were considered: the flashover current (maximum magnitude of leakage current just before flashover) and the flashover voltage. Known difficulties related to accurate measurement of these parameters which are due to parallel partial arcs on some insulators, have been quantified using control insulators and simple modelling approaches. Furthermore, the effect of insulator shape on arc length has been quantified using non-uniform pollution techniques.
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This paper reviews and discusses the rated strength of insulators as defined in ANSI, CSA, and IEC product standards. The definition of rated strength, which for a particular insulator, requires reference to the tests and acceptan...
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This paper reviews and discusses the rated strength of insulators as defined in ANSI, CSA, and IEC product standards. The definition of rated strength, which for a particular insulator, requires reference to the tests and acceptance requirements given in the appropriate standard for that insulator is discussed. An insulator may not exhibit noticeable changes at loads sufficient for the initiation of irreversible damage, referred to as its damage limit. The significance of this is discussed in the paper as insulator application loads which must be below the damage limit of the insulator and be made in accordance with the relevant standard, including consideration of the allowable variation in strength implied by strict conformance to the standard. Damage limits for ceramic and composite insulators based on the minimum allowable strength according to the current standards are given.
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Aerospace cryogenic systems require lightweight, high performance thermal insulation to preserve cryo-propellants both pre-launch and on-orbit. Current technologies have difficulty meeting all requirements, and advances in insulat...
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Aerospace cryogenic systems require lightweight, high performance thermal insulation to preserve cryo-propellants both pre-launch and on-orbit. Current technologies have difficulty meeting all requirements, and advances in insulation would benefit cryogenic upper stage launch vehicles, LH_2 fueled aircraft and ground vehicles, and provide capabilities for sub-cooled cryogens for space-borne instruments and orbital fuel depots. This paper reports the further development of load responsive multilayer insulation (LRMLI) that has a lightweight integrated vacuum shell and provides high thermal performance both in-air and on-orbit.LRMLI is being developed by Quest Product Development and Ball Aerospace under NASA contract, with prototypes designed, built, installed and successfully tested. A 3-layer LRMLI blanket (0.63 cm thick, 77 K cold, 295 K hot) had a measured heat leak of 6.6 W/m~2 in vacuum and 40.6 W/m~2 in air at one atmosphere. In-air LRMLI has an 18x advantage over Spray On Foam Insulation (SOFI) in heat leak per thickness and a 16x advantage over aerogel. On-orbit LRMLI has a 78x lower heat leak than SOFI per thickness and 6x lower heat leak than aerogel.The Phase II development of LRMLI is reported with a modular, flexible, thin vacuum shell and improved on-orbit performance. Structural and thermal analysis and testing results are presented. LRMLI mass and thermal performance is compared to SOFI, aerogel and MLI over SOFI.
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Towards the achievement of nZEB and the enormous effort for mitigating climate change effects, new sustainable construction strategies are continuously introduced and adopted in the building sector. Thermal insulation is considere...
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Towards the achievement of nZEB and the enormous effort for mitigating climate change effects, new sustainable construction strategies are continuously introduced and adopted in the building sector. Thermal insulation is considered a fundamental strategy before moving to more complex ones. Over the past 50 years, thermal insulation is mainly conceived and implemented through the steady-state heat transfer simplification, making its contribution easy to predict and control with high confidence. While historically, the concept of 'dynamic thermal insulation', or otherwise, variable thermal insulation is mainly found in warm regions, numerous recent studies show that there is a continuously growing interest in implementing it into buildings to counterbalance the few disadvantages of intense thermal insulation or to allow buildings adapting to the varying seasonal climate conditions. This interest is depicted in numerous published studies, supporting that thermal insulation can have a more beneficial and complex contribution than the steady-state assumption allows and that it can provide great potential for improving a building's energy efficiency by advancing and optimizing the envelope's thermal insulation according to the actual needs of the building on a year-round basis. In this review study, an effort to organize and classify the advances in the field is attempted, aiming at defining the complexity, the limits, the applicability and the barriers of all systems and techniques. Challenges regarding their wide utilization in the construction industry are highlighted, along with suggestions for future research. As the study shows, a few of the many approaches to dynamic thermal insulation can be simple and effective, while others show greater potential. What is more evident thought, is that further research is needed before their implementation can become practical.
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Heat transfer from opaque walls of buildings is very important for energy saving and providing thermal comfort in different climates. In this study, insulation models of opaque walls with different orientations and external, inter...
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Heat transfer from opaque walls of buildings is very important for energy saving and providing thermal comfort in different climates. In this study, insulation models of opaque walls with different orientations and external, internal and sandwich materials were numerically analyzed in terms of their time dependent thermal behaviors. The one-dimensional transient heat conduction equation was solved via the implicit finite difference method for summer and winter conditions and northern, southern, eastern and western orientations. Meteorological data for cities in Turkey with different climates, i.e., Ankara, Erzurum, Istanbul and Izmir, were used in these calculations. When the outside boundary conditions were defined by using January and July monthly averages of the daily data; the inside air temperature was assumed to be 20 degrees C and 24 degrees C in winter and summer. The results indicated that sandwich wall insulation produced more convenient heat loss and heat gain for each climate and direction. The standard deviations of the heat transfer values for the different directions were larger in summer than in winter because-of the solar radiation effect. The numerical calculations for the sandwich wall applications were carried out for different insulation thicknesses namely 0.15 m and 0.25 m, and for an uninsulated wall; the results were also compared with Turkish directive on the thermal insulation of buildings, TS825 taken as a reference condition. Compared with the insulation thickness calculated based on the TS825, the heat loss and gain values could be decreased by up to 65% and 80% for the worst winter and summer conditions. (C) 2016 Elsevier Ltd. All rights reserved.
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Buildings are designed and constructed to use their external envelope to protect people during living, working and sleeping. Nevertheless, although there are several studies on opaque wall insulation, which could reach very good i...
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Buildings are designed and constructed to use their external envelope to protect people during living, working and sleeping. Nevertheless, although there are several studies on opaque wall insulation, which could reach very good insulating performances, limited research has focused in detail on sound and thermal insulation correlation on transparent elements like windows.
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The materials used in the electrical industry have played a key role in improving the performance of electrical equipment. In spite of a number of important technological breakthroughs, the pace of development has been essentially...
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The materials used in the electrical industry have played a key role in improving the performance of electrical equipment. In spite of a number of important technological breakthroughs, the pace of development has been essentially a steady oneinvolving a process of continual improvement in material characteristics. Traditional materials are unlikely to undergo dramatic changes in the near future. However, recent discoveries in the fields of high-temperature superconductors and conductivepolymers featuring ionic of electronic conduction are likely to result in a completely new range of materials for the generation, distribution and storage of electrical energy in the first few years of the next century.
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Frequency Response Analysis (FRA) technique is commonly used to assess the mechanical integrity of power transformer core and windings. A few papers investigating the ability of FRA technique to detect bushing faults and transform...
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Frequency Response Analysis (FRA) technique is commonly used to assess the mechanical integrity of power transformer core and windings. A few papers investigating the ability of FRA technique to detect bushing faults and transformer oil degradation can be found in the literatures. However, in all of these papers, only magnitude of the FRA signature along with visual analysis was used for fault identification and quantification which may lead to inconsistent conclusions for the same FRA signature when interpreted by various personnel. As such, there is an essential need to standardize and automate the FRA interpretation process to improve its reliability and accuracy. This paper is taking a step forward toward this goal through presenting a new FRA interpretation approach by incorporating the magnitude and phase angle plots of the measured FRA signature into one polar plot that comprises more features than the conventional magnitude plot currently used for fault diagnosis. Moreover, the proposed polar plot facilitates the application of digital image processing techniques (DIP) to automate and standardize the whole process. The new proposed technique is assessed through its application to detect minor transformer bushing faults and insulating oil degradations. In this regard, two transformers of different ratings, winding structure and physical dimensions are simulated using 3D finite element analysis to implement various levels of transformer bushing faults and oil degradation. The obtained FRA polar plots of the two investigated transformers under various bushings and oil health conditions are manipulated using the developed DIP codes to investigate the impact of each fault type / level on the proposed polar plot signature. Also, Practical measurements are performed to validate simulation results and evaluate the feasibility of the proposed technique. Results show the ability of the proposed technique to automate the detection of minor levels of bushing faults and insulating oil degradation with a high degree of accuracy.
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An alternative to cellulose- and foam-based insulation materials, fiberglass can address some of the most serious concerns involving insulation and indoor air quality (IAQ), such as mold and (especially) formaldehyde.
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