Caracteriza����o experimental e num��rica do desempenho t��rmico de um edif��cio "gaioleiro": identifica����o de oportunidades de melhoria

O sector dos edif��cios �� respons��vel por uma percentagem significativa dos consumos de energia prim��ria e de energia el��ctrica em Portugal, associada principalmente ao conforto t��rmico dos seus ocupantes. A Uni��o Europeia pretende uma redu����o de 20%, at�� 2020, dos consumos de energia e consequentes emiss��es de CO2 atrav��s da melhoria da efici��ncia energ��tica dos edif��cios p��blicos e residenciais. Em Portugal, o Plano Nacional para a Efici��ncia Energ��tica (PNAEE) tem por objectivo obter uma poupan��a anual de energia de pelo menos 1% at�� ao ano de 2016, tomando como base a m��dia de consumos de energia final, registados entre 2001 e 2005. Neste contexto, os edif��cios anteriores a 1990 (primeira vers��o do RCCTE) podem apresentar um potencial significativo de melhoria da sua efici��ncia energ��tica com base na sua reabilita����o. Os edif��cios ���Gaioleiros��� (1880 ��� 1930) constituindo uma parte importante do patrim��nio hist��rico da cidade de Lisboa, para os quais a informa����o sobre o seu desempenho t��rmico �� limitada, considerou-se pertinente efectuar um estudo destinado �� sua caracteriza����o experimental e num��rica, face �� especificidade do comportamento t��rmico das suas paredes caracterizadas pela elevada espessura. No presente trabalho, apresenta-se a metodologia e os resultados experimentais da medi����o da resist��ncia t��rmica das paredes e da medi����o das necessidades t��rmicas de aquecimento da habita����o. Estes resultados experimentais foram utilizados na valida����o do modelo de simula����o t��rmica da habita����o, que posteriormente serviu para avaliar as suas necessidades t��rmicas de aquecimento (Nic) e de arrefecimento (Nvc), identificar oportunidades de melhoria e avaliar o respectivo potencial de reabilita����o. Neste trabalho, como contributos para uma reabilita����o sustent��vel, apresentam-se avalia����es de oportunidades de melhoria com base em estrat��gias de refor��o do isolamento t��rmico. Dos resultados obtidos concluiu-se que melhorando o isolamento t��rmico das paredes e v��os envidra��ados �� poss��vel baixar consideravelmente os consumos de energia associados �� habita����o, cumprindo assim as exig��ncias estabelecidas no RCCTE ao n��vel dos requisitos de qualidade t��rmica da envolvente e consumos energ��ticos para edif��cios novos e grandes reabilita����es.

Manuten����o de edif��cios: manuten����o das instala����es t��cnicas de um grande edif��cio

Este relat��rio de est��gio, que se realizou no Edif��cio Atrium Saldanha em Lisboa, tem por finalidade demonstrar as aptid��es adquiridas no decorrer do Mestrado e que tornaram poss��veis a participa����o num est��gio que envolveu v��rias ��reas da Engenharia Mec��nica. Nos ��ltimos anos, tem-se assistido a um crescente aumento do consumo e do custo da energia el��ctrica. De acordo com an��lises realizadas pela Uni��o Europeia, uma percentagem significativa deste aumento de consumo est�� relacionado com edif��cios e habita����es. A manuten����o preventiva das instala����es t��cnicas ��, entre outros aspectos, uma das ferramentas essenciais na redu����o desta factura energ��tica. A quest��o que se coloca relaciona-se com a metodologia a aplicar para esse efeito. De que forma podem ou devem os planos de manuten����o ser elaborados, qual a periodicidade das interven����es a considerar de modo a aumentar a efici��ncia energ��tica dos edif��cios, reduzir as emiss��es de di��xido de carbono e garantir uma maior protec����o do utilizador? Numa fase inicial do est��gio foi feita uma caracteriza����o geral das principais instala����es t��cnicas do edif��cio de modo a se analisarem, posteriormente, os procedimentos de manuten����o adoptados pelas equipas de manuten����o. Foram ainda sugeridas algumas periodicidades para os procedimentos de manuten����o j�� existentes e algumas interven����es que n��o estavam inclu��das no plano de manuten����o do edif��cio e que podem contribuir para aumentar a fiabilidade dos equipamentos e consequentemente a efici��ncia energ��tica e a qualidade do ar interior dos edif��cios.

Utiliza����o racional de energia el��ctrica no munic��pio de Vila Franca de Xira: casos de estudo

O objectivo pretendido alcan��ar �� o de obter uma redu����o nos consumos de energia el��ctrica do Munic��pio de Vila Franca de Xira, recorrendo �� URE. Esta URE consiste num conjunto de ac����es e/ou medidas e/ou procedimentos e/ou equipamentos cuja aplica����o tem como fim, o de potenciar uma utiliza����o e uma gest��o mais racional e rent��vel da energia - da�� se podendo dizer, cada vez mais, que a mesma �� um factor essencial de economia energ��tica, logo, de redu����o de custos. A aplica����o destas ac����es e/ou medidas e/ou procedimentos e/ou equipamentos dever��, por isso, ser extens��vel aos Munic��pios, com o fim de fazer reduzir uma factura energ��tica de grande peso e significado, a qual, em tempos que s��o de profunda crise econ��mica, pode tornar problem��tico ou at�� mesmo hipotecar, o respectivo futuro. Assim e se por um lado existe no Munic��pio um conjunto alargado de situa����es estabelecidas sem crit��rios de racionabilidade energ��tica e ��s quais, todavia, �� j�� poss��vel fazer aplicar essas ac����es e/ou medidas e/ou procedimentos e/ou equipamentos de URE, por outro lado, �� da�� garantido que se poder�� alcan��ar a pretendida redu����o dos consumos energ��ticos do Munic��pio, sempre assegurando e mantendo o conforto e a produtividade das actividades dependentes dessa energia. Com esse objectivo e partindo da an��lise de um conjunto de instala����es e/ou equipamentos j�� existentes ou com possibilidades de virem a ser estabelecidas/os pelo Munic��pio, �� pretendido definir, estudar e classificar, um conjunto de dados que tendam a desenvolver, potenciar e justificar a decis��o da sua aplica����o. Um conjunto alargado de exemplos pr��ticos ou Casos de Estudo ser��o desenvolvidos, tentando chegar a conclus��es sobre a viabilidade econ��mica das solu����es apresentadas e, da��, da decis��o da oportunidade da execu����o do conjunto de trabalhos inerentes �� aplica����o desse tipo de situa����o.

Caracteriza����o experimental e num��rica da permeabilidade ao ar da envolvente e do sistema de ventila����o de um edif��cio "Gaioleiro"

Os edif��cios do tipo ���Gaioleiro���, em continuidade com os edif��cios do tipo Pombalino, s��o um conjunto arquitect��nico e cultural de elevada import��ncia, expressivo na cidade de Lisboa, sendo fundamental a sua conserva����o e reabilita����o para responder a algumas das actuais preocupa����es relacionadas com a seguran��a (funcional, estrutural e construtiva), efici��ncia energ��tica e valoriza����o deste edificado. A conserva����o de energia e actual regulamenta����o de efici��ncia energ��tica nos edif��cios de habita����o, baseada nos princ��pios da Directiva Europeia relativa ao Desempenho Energ��tico de Edif��cios 2002/91/EC (EPBD - Energy Performance of Buildings Directives), aplicam-se a edif��cios novos e a grandes reabilita����es. Contudo, a conserva����o de energia �� uma preocupa����o transversal (ambiental, econ��mica e social) e nas ��ltimas d��cadas tem sido objecto de investiga����o. No entanto, a caracteriza����o experimental de sistemas de ventila����o e a sua influ��ncia no desempenho t��rmico de edif��cios �� escassa, n��o se conhecendo trabalhos em edif��cios ���Gaioleiros���. Para a correcta avalia����o da efici��ncia energ��tica das solu����es de reabilita����o a implementar nestes edif��cios �� essencial o estudo do seu sistema de ventila����o natural. A presente disserta����o pretende caracterizar experimentalmente o sistema de ventila����o de um edif��cio ���Gaioleiro��� atrav��s de ensaios de pressuriza����o e de g��s tra��ador. Os ensaios de pressuriza����o destinam-se a avaliar a permeabilidade ao ar das componentes que integram a envolvente, e assim, suportar a estimativa da taxa de infiltra����es de ar. Os ensaios com gases tra��adores destinam-se a medir a taxa m��dia de renova����o de ar, tendo sido, neste trabalho, avaliadas as taxas de renova����o de ar para a condi����o actual, para uma condi����o de melhoria da permeabilidade ao arda envolvente e para a condi����o de tamb��m ser aplicado um exaustor na chamin��. Esta avalia����o experimental permitiu suportar o desenvolvimento e valida����o do modelo num��rico de simula����o da ventila����o. Com este modelo validado s��o estimadas as taxas m��dias de ventila����o e s��o estudadas oportunidades de melhoria de acordo com as exig��ncias de qualidade do ar interior e de efici��ncia energ��tica, como contributo para uma constru����o (reabilita����o) sustent��vel. Do trabalho experimental foi evidenciado que se for exclusivamente melhorada a permeabilidade do ar da envolvente existe um elevado risco da taxa de ventila����o ser insuficiente, apesar de no Regulamento das Caracter��sticas de Comportamento T��rmico dos Edif��cios (RCCTE) serem previstas taxas de renova����o mais elevadas para essa nova situa����o. Conclui-se que a caixilharia �� o elemento que mais contribui para a permeabilidade ao ar da envolvente (60%). A permeabilidade ao ar deste edif��cio �� muito elevada, sendo poss��vel melhorar substancialmente (reduzir em 50% as necessidades nominais anuais de energia ��til para aquecimento) atrav��s de interven����es ao n��vel das janelas e das gralhas de admiss��o de ar.

Fractional-order control and simulation of wind energy systems with PMSG/full-power converter topology

This paper presents a new integrated model for the simulation of wind energy systems. The proposed model is more realistic and accurate, considering a variable-speed wind turbine, two-mass rotor, permanent magnet synchronous generator (PMSG), different power converter topologies, and filters. Additionally, a new control strategy is proposed for the variable-speed operation of wind turbines with PMSG/full-power converter topology, based on fractional-order controllers. Comprehensive simulation studies are carried out with matrix and multilevel power converter topologies, in order to adequately assert the system performance in what regards the quality of the energy injected into the electric grid. Finally, conclusions are duly drawn.

The problem of estimating the volatility of zero coupon bond interest rate

Financial literature and financial industry use often zero coupon yield curves as input for testing hypotheses, pricing assets or managing risk. They assume this provided data as accurate. We analyse implications of the methodology and of the sample selection criteria used to estimate the zero coupon bond yield term structure on the resulting volatility of spot rates with different maturities. We obtain the volatility term structure using historical volatilities and Egarch volatilities. As input for these volatilities we consider our own spot rates estimation from GovPX bond data and three popular interest rates data sets: from the Federal Reserve Board, from the US Department of the Treasury (H15), and from Bloomberg. We find strong evidence that the resulting zero coupon bond yield volatility estimates as well as the correlation coefficients among spot and forward rates depend significantly on the data set. We observe relevant differences in economic terms when volatilities are used to price derivatives.

Light pollution and energy efficiency: a case study of the village of Vialonga

Since industrialization and the formation of larger urban centers in the nineteenth century, pollution of the environment was always present in daily life in various ways, namely in the form of light. Light pollution can cause various consequences, both for humans and for their ecosystem, producing effects on environmental, social, economic and scientific level. In Portugal, the lighting is responsible for 3% of total electricity consumption, energy costs are in some cases more than 50% towards the costs incurred by municipalities with energy, checking-in recent years a trend similar to that improvement of illumination levels in the region (about 4 to 5% per year). Proper use of lighting brings many benefits both to the citizen and environment, since greater energy efficiency can contribute to reducing CO2 emissions, energy costs, as well as to decrease the use of resources not-renewable and/or contamination of renewable resources, which can occurs in the process of obtaining electricity. The present study has a main goal to analyze the illuminance levels associated to the public lighting of the village of Vialonga, Vila Franca de Xira (Portugal), to verify if it is efficient. The aim is also to relate the efficiency of street lighting with the existence of light pollution.

Effect of the number of shells on the pressure and energy of two-dimensional free bubble clusters

We have performed Surface Evolver simulations of two-dimensional hexagonal bubble clusters consisting of a central bubble of area lambda surrounded by s shells or layers of bubbles of unit area. Clusters of up to twenty layers have been simulated, with lambda varying between 0.01 and 100. In monodisperse clusters (i.e., for lambda = 1) [M.A. Fortes, F Morgan, M. Fatima Vaz, Philos. Mag. Lett. 87 (2007) 561] both the average pressure of the entire Cluster and the pressure in the central bubble are decreasing functions of s and approach 0.9306 for very large s, which is the pressure in a bubble of an infinite monodisperse honeycomb foam. Here we address the effect of changing the central bubble area lambda. For small lambda the pressure in the central bubble and the average pressure were both found to decrease with s, as in monodisperse clusters. However, for large,, the pressure in the central bubble and the average pressure increase with s. The average pressure of large clusters was found to be independent of lambda and to approach 0.9306 asymptotically. We have also determined the cluster surface energies given by the equation of equilibrium for the total energy in terms of the area and the pressure in each bubble. When the pressures in the bubbles are not available, an approximate equation derived by Vaz et al. [M. Fatima Vaz, M.A. Fortes, F. Graner, Philos. Mag. Lett. 82 (2002) 575] was shown to provide good estimations for the cluster energy provided the bubble area distribution is narrow. This approach does not take cluster topology into account. Using this approximate equation, we find a good correlation between Surface Evolver Simulations and the estimated Values of energies and pressures. (C) 2008 Elsevier B.V. All rights reserved.

The condensation and ordering of models of empty liquids

We consider a simple model consisting of particles with four bonding sites ("patches"), two of type A and two of type B, on the square lattice, and investigate its global phase behavior by simulations and theory. We set the interaction between B patches to zero and calculate the phase diagram as the ratio between the AB and the AA interactions, epsilon(AB)*, varies. In line with previous work, on three-dimensional off-lattice models, we show that the liquid-vapor phase diagram exhibits a re-entrant or "pinched" shape for the same range of epsilon(AB)*, suggesting that the ratio of the energy scales - and the corresponding empty fluid regime - is independent of the dimensionality of the system and of the lattice structure. In addition, the model exhibits an order-disorder transition that is ferromagnetic in the re-entrant regime. The use of low-dimensional lattice models allows the simulation of sufficiently large systems to establish the nature of the liquid-vapor critical points and to describe the structure of the liquid phase in the empty fluid regime, where the size of the "voids" increases as the temperature decreases. We have found that the liquid-vapor critical point is in the 2D Ising universality class, with a scaling region that decreases rapidly as the temperature decreases. The results of simulations and theoretical analysis suggest that the line of order-disorder transitions intersects the condensation line at a multi-critical point at zero temperature and density, for patchy particle models with a re-entrant, empty fluid, regime. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3657406]

A DC-DC Step-Up mu-Power Converter for Energy Harvesting Applications, Using Maximum Power PointTracking, Based on Fractional Open Circuit Voltage

A DC-DC step-up micro power converter for solar energy harvesting applications is presented. The circuit is based on a switched-capacitorvoltage tripler architecture with MOSFET capacitors, which results in an, area approximately eight times smaller than using MiM capacitors for the 0.131mu m CMOS technology. In order to compensate for the loss of efficiency, due to the larger parasitic capacitances, a charge reutilization scheme is employed. The circuit is self-clocked, using a phase controller designed specifically to work with an amorphous silicon solar cell, in order to obtain themaximum available power from the cell. This will be done by tracking its maximum power point (MPPT) using the fractional open circuit voltage method. Electrical simulations of the circuit, together with an equivalent electrical model of an amorphous silicon solar cell, show that the circuit can deliver apower of 1132 mu W to the load, corresponding to a maximum efficiency of 66.81%.

A generalized notion of compliance

It is a known fact in structural optimization that for structures subject to prescribed non-zero displacements the work done by the loads is not agood measure of compliance, neither is the stored elastic energy. We briefly discuss a possible alternative measure of compliance, valid for general boundary conditions. We also present the adjoint states (necessary for the computation of the structural derivative) for the three functionals under consideration. (C) 2011 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.

A risk-averse optimization model for trading wind energy in a market environment under uncertainty

In this paper, a stochastic programming approach is proposed for trading wind energy in a market environment under uncertainty. Uncertainty in the energy market prices is the main cause of high volatility of profits achieved by power producers. The volatile and intermittent nature of wind energy represents another source of uncertainty. Hence, each uncertain parameter is modeled by scenarios, where each scenario represents a plausible realization of the uncertain parameters with an associated occurrence probability. Also, an appropriate risk measurement is considered. The proposed approach is applied on a realistic case study, based on a wind farm in Portugal. Finally, conclusions are duly drawn. (C) 2011 Elsevier Ltd. All rights reserved.

A Step-up mu-Power Converter for Solar Energy Harvesting Applications, using Hill Climbing Maximum Power Point Tracking

This paper presents a step-up micro-power converter for solar energy harvesting applications. The circuit uses a SC voltage tripler architecture, controlled by an MPPT circuit based on the Hill Climbing algorithm. This circuit was designed in a 0.13 mu m CMOS technology in order to work with an a-Si PV cell. The circuit has a local power supply voltage, created using a scaled down SC voltage tripler, controlled by the same MPPT circuit, to make the circuit robust to load and illumination variations. The SC circuits use a combination of PMOS and NMOS transistors to reduce the occupied area. A charge re-use scheme is used to compensate the large parasitic capacitors associated to the MOS transistors. The simulation results show that the circuit can deliver a power of 1266 mu W to the load using 1712 mu W of power from the PV cell, corresponding to an efficiency as high as 73.91%. The simulations also show that the circuit is capable of starting up with only 19% of the maximum illumination level.

Short-term wind forecasting for energy resources scheduling

This paper proposes a wind power forecasting methodology based on two methods: direct wind power forecasting and wind speed forecasting in the first phase followed by wind power forecasting using turbines characteristics and the aforementioned wind speed forecast. The proposed forecasting methodology aims to support the operation in the scope of the intraday resources scheduling model, namely with a time horizon of 5 minutes. This intraday model supports distribution network operators in the short-term scheduling problem, in the smart grid context. A case study using a real database of 12 months recorded from a Portuguese wind power farm was used. The results show that the straightforward methodology can be applied in the intraday model with high wind speed and wind power accuracy. The wind power forecast direct method shows better performance than wind power forecast using turbine characteristics and wind speed forecast obtained in first phase.

Real-time energy resources scheduling considering intensive wind penetration

The use of distributed energy resources, based on natural intermittent power sources, like wind generation, in power systems imposes the development of new adequate operation management and control methodologies. A short-term Energy Resource Management (ERM) methodology performed in two phases is proposed in this paper. The first one addresses the day-ahead ERM scheduling and the second one deals with the five-minute ahead ERM scheduling. The ERM scheduling is a complex optimization problem due to the high quantity of variables and constraints. In this paper the main goal is to minimize the operation costs from the point of view of a virtual power player that manages the network and the existing resources. The optimization problem is solved by a deterministic mixedinteger non-linear programming approach. A case study considering a distribution network with 33 bus, 66 distributed generation, 32 loads with demand response contracts and 7 storage units and 1000 electric vehicles has been implemented in a simulator developed in the field of the presented work, in order to validate the proposed short-term ERM methodology considering the dynamic power system behavior.