40 research outputs found

    Methods and tools for the assessment of daylight transmittance through expanded metal meshes

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    306 p.El metal expandido es un producto industrial de amplia aplicación en envolventes arquitectónicas. Su función fundamental es la de protección solar, pero no ha sido analizado con precisión. He analizado la transmitancia luminosa. El objetivo es crear herramientas y métodos de análisis de la transmitancia lumínica del metal expandido y probar su validez. Los métodos existentes no están adaptados al metal expandido y éste ofrece una diversidad de variantes incontable. En este trabajo, entre otras cosas, se desarrolla un modelador tridimensional automatizado de metal expandido y se ensayan modos de análisis por medio de las herramientas informáticas existentes

    Desarrollo de circuitos electrónicos para la extracción y conversión en energía eléctrica de la vibración aplicada a materiales piezoeléctricos

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    xx,145 p.Esta tesis trata sobre los retos que plantea la recolección de energías ambientales debaja potencia para convertirla en fuentes de alimentación de dispositivos electrónicos de bajoconsumo. A diferencia de las energías renovables más comunes, eólica y fotovoltaica, quemanejan importantes niveles de potencia, estas otras energías ambientales pueden llegar agenerar potencias del orden de microvatios o, como máximo, unas decenas de milivatios. Pesea que cuantitativamente puedan ser consideradas fuentes con una aportación energética muylimitada, el beneficio derivado de disponer de sistemas electrónicos autoalimentados de modoindefinido puede llegar a ser muy importante.En el esfuerzo que está suponiendo el desarrollo de estas tecnologías participandiferentes áreas de las ciencias de materiales y la ingeniería. Desde la perspectiva de laingeniería electrónica, las nuevas tecnologías de fabricación microscópicas posibilitan laproducción de componentes con niveles de integración crecientes, funcionalidades másamplias y consumos más reducidos. Estos complejos sistemas integrados empaquetados enuna pastilla intentan ir más allá en su desarrollo al incorporar una unidad interna generadoraque alimente el conjunto. Todo ello con el objetivo final de producir sistemas de sensoreselectrónicos autoalimentados para aplicaciones ubicadas en zonas remotas de difícil acceso ocondiciones ambientales extremas. Los diseños de las unidades internas generadoras se basanen circuitos electrónicos que previamente han sido testados utilizando componentes discretosy que se adaptan convenientemente para su integración en el chip. Es aquí, en este campo delos circuitos de gestión de energía eficientes donde se centra el trabajo de investigación deesta tesis. El objetivo que se plantea en la tesis es analizar, investigar y desarrollar nuevoscircuitos electrónicos que sean útiles para captar las energías ambientales de baja potencia yconvertirlas en energía eléctrica apta para la alimentación de dispositivos electrónicos de bajoconsumo.Se ha hecho un especial énfasis en los circuitos capaces de trabajar con múltiplesfuentes generadoras y que obtengan el máximo rendimiento en la transferencia de energía. Elobjetivo final es obtener mayores niveles de energía, necesarios para alimentar de modoautónomo dispositivos de bajas y medias potencias.La tesis incluye tanto el trabajo de documentación del estado del arte como lasaportaciones propias, validadas en una serie de ensayos experimentales de laboratorio y decampo

    Daylight transmittance through Expanded Metal shadings

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    Due to the substantial need for energy efficiency, the daylight performance of building envelopes is a key issue in sustainable architecture. A frequently used shading system consists on static expanded metal meshes (EM). As a very prominent textural facade element, expanded metal is widely used as both a cladding and static shading device. One first aim is to provide a sufficient description of EM, including fabrication, possible usage and overall properties. This includes a set of parameters needed to control accurately the complex geometry of EM. Those parameters are also useful to get reliable 3-D computer models of EM. The main objective of this paper is to assess, describe and compare EM light transmittance performance as a shading device. We were specifically looking to determine the influence of parameters such as geometry, colour, position and direction of incoming light on the shading performance. The research is based on BSDF simulations via Radiance and experimental data provided at a previous laboratory stage. We have simulated and compared the performance of various EM shading devices for a south exposed façade in Madrid in most characteristic times of the year: solstices and equinoxes, as well as midday transmittance throughout the year

    Microstructured glazing for daylighting, glare protection, seasonal thermal control and clear view

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    The appropriate choice of glazing in a facade depends on many factors. They include amongst other criteria: location, orientation, climatic condition, energetic efficiency, usage of the building, required user comfort, and the architectural concept. On the south facade of high-rise buildings in particular, it is a challenge to have simultaneously large glazed area, no glare, no excessive cooling loads, a clear view and sufficient natural light flux. In Switzerland, electric lighting, heating and air conditioning account for about 74% of the total energy demand in private housing and 32% of the overall Swiss electricity usage. This energy consumption can be strongly influenced by using the most appropriate fenestration system. A software was developed during this thesis to engineer new complex fenestration system (CFS) that have a two dimensional profile. The originality of the implemented Monte Carlo ray tracing algorithm is the separation of intersection and interaction. The model also calculates an accurate bidirectional transmission distribution function that is used in combination with Radiance to obtain a rendering of the daylighting distribution in an office space or dynamic daylight metrics such as the daylight factor and daylight autonomy. Finally, to estimate the thermal performances, a simple nodal thermal model was added to simulate the temperature evolution and the thermal loads in a given office. This tool was validated. A glazing combining several functions and that can contribute to significantly reduce energy consumption in buildings was developed using this novel ray tracing approach. It was designed to obtain a strongly angular dependent transmission and a specific angular distribution of transmitted light. The engineered geometry provides elevated daylight illuminance by redirecting the incoming light towards the depth of the room. This redirection simultaneously reduces the glare risk. For an optimised usage of available solar radiation, the transmission of direct sunlight is maximised in winter and minimised in summer. Taking advantage of the changing elevation of the sun between seasons, such a seasonal variation can be created by a strongly angular dependent transmittance. A fabrication process was identified and samples of embedded micromirrors were produced to demonstrate the feasibility. The fabrication of such structures required several steps. The fabrication of a metallic mould with a high aspect ratio and mirror polished surfaces is followed by the production of an intermediate polydimethylsiloxane mould that was subsequently used to replicate the structure with a ultraviolet (UV) curable polymer. Selected facets of these samples were then coated with a thin film of reflective material. Finally, the structures were filled with the same polymer to integrated the mirrors. The blocking effect can be obtained by a combination with well placed reflective stripes, those were fabricated by lift-off lithography. The samples were characterised during the various fabrication steps using various microscopy techniques, energy-dispersive X-ray spectroscopy, profilometry and optical measurements. A setup was built for the measures of angular dependent transmittance. The final samples redirect up to 70% of the light flux and are very transparent when looking through at normal incidence

    Towards Space-like Photometric Precision from the Ground with Beam-Shaping Diffusers

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    We demonstrate a path to hitherto unachievable differential photometric precisions from the ground, both in the optical and near-infrared (NIR), using custom-fabricated beam-shaping diffusers produced using specialized nanofabrication techniques. Such diffusers mold the focal plane image of a star into a broad and stable top-hat shape, minimizing photometric errors due to non-uniform pixel response, atmospheric seeing effects, imperfect guiding, and telescope-induced variable aberrations seen in defocusing. This PSF reshaping significantly increases the achievable dynamic range of our observations, increasing our observing efficiency and thus better averages over scintillation. Diffusers work in both collimated and converging beams. We present diffuser-assisted optical observations demonstrating 6216+2662^{+26}_{-16}ppm precision in 30 minute bins on a nearby bright star 16-Cygni A (V=5.95) using the ARC 3.5m telescope---within a factor of \sim2 of Kepler's photometric precision on the same star. We also show a transit of WASP-85-Ab (V=11.2) and TRES-3b (V=12.4), where the residuals bin down to 18041+66180^{+66}_{-41}ppm in 30 minute bins for WASP-85-Ab---a factor of \sim4 of the precision achieved by the K2 mission on this target---and to 101ppm for TRES-3b. In the NIR, where diffusers may provide even more significant improvements over the current state of the art, our preliminary tests have demonstrated 13736+64137^{+64}_{-36}ppm precision for a KS=10.8K_S =10.8 star on the 200" Hale Telescope. These photometric precisions match or surpass the expected photometric precisions of TESS for the same magnitude range. This technology is inexpensive, scalable, easily adaptable, and can have an important and immediate impact on the observations of transits and secondary eclipses of exoplanets.Comment: Accepted for publication in ApJ. 30 pages, 20 figure

    The EarthCARE mission – science and system overview

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    The Earth Cloud, Aerosol and Radiation Explorer (EarthCARE) is a satellite mission implemented by the European Space Agency (ESA), in cooperation with the Japan Aerospace Exploration Agency (JAXA), to measure global profiles of aerosols, clouds and precipitation properties together with radiative fluxes and derived heating rates. The simultaneous measurements of the vertical structure and horizontal distribution of cloud and aerosol fields, together with outgoing radiation, will be used in particular to evaluate their representation in weather forecasting and climate models and to improve our understanding of cloud and aerosol radiative impact and feedback mechanisms. To achieve the objective, the goal is that a retrieved scene with footprint size of 10 km × 10 km is measured with sufficiently high resolution that the atmospheric vertical profile of short-wave (solar) and long-wave (thermal) flux can be reconstructed with an accuracy of 10 W m−2 at the top of the atmosphere. To optimise the performance of the two active instruments, the platform will fly at a relatively low altitude of 393 km, with an equatorial revisit time of 25 d. The scientific payload consists of four instruments: an atmospheric lidar, a cloud-profiling radar with Doppler capability, a multi-spectral imager and a broadband radiometer. Co-located measurements from these instruments are processed in the ground segment, which produces and distributes a wide range of science data products. As well as the Level 1 (L1) product of each instrument, a large number of multiple-instrument L2 products have been developed, in both Europe and Japan, benefiting from the data synergy. An end-to-end simulator and several test scenes have been developed that simulate EarthCARE observations and provide a development and test environment for L1 and L2 processors. Within this paper the EarthCARE observational requirements are addressed. An overview is given of the space segment with a detailed description of the four science instruments, demonstrating how the observational requirements will be met. Furthermore, the elements of the space segment and ground segment that are relevant for science data users are described and the data products are introduced.</p

    Applicability of climate-based daylight modelling

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    This PhD thesis evaluated the applicability of Climate-Based Daylight Modelling (CBDM) as it is presently done. The objectives stated in this thesis aimed at broadly assessing applicability by looking at multiple aspects: (i) the way CBDM is used by expert researchers and practitioners; (ii) how state-of-the-art simulation techniques compare to each other and how they are affected by uncertainty in input factors; (iii) how the simulated results compare with data measured in real occupied spaces. The answers obtained from a web-based questionnaire portrayed a variety of workflows used by different people to perform similar, if not the same, evaluations. At the same time, the inter-model comparison performed to compare the existing simulation techniques revealed significant differences in the way the sky and the sun are recreated by each technique. The results also demonstrated that some of the annual daylight metrics commonly required in building guidelines are sensitive to the choice of simulation tool, as well as other input parameters, such as climate data, orientation and material optical properties. All the analyses were carried out on four case study spaces, remodelled from existing classrooms that were the subject of a concurrent research study that monitored their interior luminous conditions. A large database of High Dynamic Range images was collected for that study, and the luminance data derived from these images could be used in this work to explore a new methodology to calibrate climate-based daylight models. The results collected and presented in this dissertation illustrate how, at the time of writing, there is not a single established common framework to follow when performing CBDM evaluations. Several different techniques coexist but each of them is characterised by a specific domain of applicability

    Light absorption enhancement and electronic properties of thin-film solar cells

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    In this work we developed several strategies to enhance solar cells which lead to stronger sunlight absorption with less active material and thereby also reducing costs. This is accomplished through utilizing nanoscale architectures, which geometry can be tailored to modify the flow of light for optimal absorption. Since sunlight comprises of photons with a broad range of wavelength (colors), ensuring a complete absorption requires sophistications in the nanostructure design due to its wavelength dependent interaction with light. To address this challenge we utilized combinations of different periodic nanostructures with one another and also with disordered rough light diffusers. Aside from our absorption enhancement work, we also investigated light emission enhancement utilizing periodically placed metal nanoantennas. We demonstrate how hybrid plasmonic-photonic modes that arise in such system can be used to control and enhance emission over an extended spatial region. This is relevant in solar cell enhancement schemes which convert the unused portion of sunlight into the color range suitable for optimal usage. Having investigated various light management schemes to enhance solar cells, we proceeded to examine the limiting factors which hinder efficient electrical current extraction from polycrystalline silicon thin film solar cells of a few micrometers thick. We identified the conditions in which this more economical material gives the desired solar cell performance
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