Cell (module) temperature regulated performance of a building integrated photovoltaic system in tropical conditions

The performance of a building integrated photovoltaic system (BIPV) has to be commendable, not only on the electrical front but also on the thermal comfort front, thereby fulfilling the true responsibility of an energy providing shelter. Given the low thermal mass of BIPV systems, unintended and undesired outcomes of harnessing solar energy - such as heat gain into the building, especially in tropical regions - have to be adequately addressed. Cell (module) temperature is one critical factor that affects both the electrical and the thermal performance of such installations. The current paper discusses the impact of cell (module) temperature on both the electrical efficiency and thermal comfort by investigating the holistic performance of one such system (5.25 kW(p)) installed at the Centre for Sustainable Technologies in the Indian Institute of Science, Bangalore. Some recommendations (passive techniques) for improving the performance and making BIPV structures thermally comfortable have been listed out. (C) 2014 Elsevier Ltd. All rights reserved.

Assessing impact of material transition and thermal comfort models on embodied and operational energy in vernacular dwellings (India)

Vernacular dwellings are well-suited climate-responsive designs that adopt local materials and skills to support comfortable indoor environments in response to local climatic conditions. These naturally-ventilated passive dwellings have enabled civilizations to sustain even in extreme climatic conditions. The design and physiological resilience of the inhabitants have coevolved to be attuned to local climatic and environmental conditions. Such adaptations have perplexed modern theories in human thermal-comfort that have evolved in the era of electricity and air-conditioned buildings. Vernacular local building elements like rubble walls and mud roofs are given way to burnt brick walls and reinforced cement concrete tin roofs. Over 60% of Indian population is rural, and implications of such transitions on thermal comfort and energy in buildings are crucial to understand. Types of energy use associated with a buildings life cycle include its embodied energy, operational and maintenance energy, demolition and disposal energy. Embodied Energy (EE) represents total energy consumption for construction of building, i.e., embodied energy of building materials, material transportation energy and building construction energy. Embodied energy of building materials forms major contribution to embodied energy in buildings. Operational energy (OE) in buildings mainly contributed by space conditioning and lighting requirements, depends on the climatic conditions of the region and comfort requirements of the building occupants. Less energy intensive natural materials are used for traditional buildings and the EE of traditional buildings is low. Transition in use of materials causes significant impact on embodied energy of vernacular dwellings. Use of manufactured, energy intensive materials like brick, cement, steel, glass etc. contributes to high embodied energy in these dwellings. This paper studies the increase in EE of the dwelling attributed to change in wall materials. Climatic location significantly influences operational energy in dwellings. Buildings located in regions experiencing extreme climatic conditions would require more operational energy to satisfy the heating and cooling energy demands throughout the year. Traditional buildings adopt passive techniques or non-mechanical methods for space conditioning to overcome the vagaries of extreme climatic variations and hence less operational energy. This study assesses operational energy in traditional dwelling with regard to change in wall material and climatic location. OE in the dwellings has been assessed for hot-dry, warm humid and moderate climatic zones. Choice of thermal comfort models is yet another factor which greatly influences operational energy assessment in buildings. The paper adopts two popular thermal-comfort models, viz., ASHRAE comfort standards and TSI by Sharma and Ali to investigate thermal comfort aspects and impact of these comfort models on OE assessment in traditional dwellings. A naturally ventilated vernacular dwelling in Sugganahalli, a village close to Bangalore (India), set in warm - humid climate is considered for present investigations on impact of transition in building materials, change in climatic location and choice of thermal comfort models on energy in buildings. The study includes a rigorous real time monitoring of the thermal performance of the dwelling. Dynamic simulation models validated by measured data have also been adopted to determine the impact of the transition from vernacular to modern material-configurations. Results of the study and appraisal for appropriate thermal comfort standards for computing operational energy has been presented and discussed in this paper. (c) 2014 K.I. Praseeda. Published by Elsevier Ltd.

Performance Analysis of Heat Sinks With Phase-Change Materials Subjected to Transient and Cyclic Heating

Phase-change cooling technique is a suitable method for thermal management of electronic equipment subjected to transient or cyclic heat loads. The thermal performance of a phase-change based heat sink under cyclic heat load depends on several design parameters, namely, applied heat flux, cooling heat transfer coefficient, thermophysical properties of phase-change materials (PCMs), and physical dimensions of phase-change storage system during melting and freezing processes. A one-dimensional conduction heat transfer model is formulated to evaluate the effectiveness of preliminary design of practical PCM-based energy storage units. In this model, the phase-change process of the PCM is divided into melting and solidification subprocesses, for which separate equations are written. The equations are solved sequentially and an explicit closed-form solution is obtained. The efficacy of analytical model is estimated by comparing with a finite-volume-based numerical solution for both transient and cyclic heat loads.

Energy retrofits in social housing. Analysis of its thermal behaviour.

468 p.

Predicting the performance of an office under climate change: A study of metrics, sensitivity and zonal resolution

Climate change is expected to have significant impact on the future thermal performance of buildings. Building simulation and sensitivity analysis can be employed to predict these impacts, guiding interventions to adapt buildings to future conditions. This article explores the use of simulation to study the impact of climate change on a theoretical office building in the UK, employing a probabilistic approach. The work studies (1) appropriate performance metrics and underlying modelling assumptions, (2) sensitivity of computational results to identify key design parameters and (3) the impact of zonal resolution. The conclusions highlight the importance of assumptions in the field of electricity conversion factors, proper management of internal heat gains, and the need to use an appropriately detailed zonal resolution. © 2010 Elsevier B.V. All rights reserved.

Winglets for Improved Aerothermal Performance of High Pressure Turbines

This paper investigates the design of winglet tips for unshrouded high pressure turbine rotors, considering aerodynamic and thermal performance simultaneously. A novel parameterization method has been developed to alter the tip geometry of a rotor blade. A design survey of un-cooled, flat-tipped winglets is performed using RANS calculations for a single rotor at engine representative operating conditions. Compared to a plain tip, large efficiency gains can be realized by employing an overhang around the full perimeter of the blade, but the overall heat load rises significantly. By employing an overhang on only the early suction surface, significant efficiency improvements can be obtained without increasing the overall heat transfer to the blade. The flow physics are explored in detail to explain the results. For a plain tip, the leakage and passage vortices interact to create a three-dimensional impingement onto the blade suction surface, causing high heat transfer. The addition of an overhang on the early suction surface displaces the tip leakage vortex away from the blade, weakening the impingement effect and reducing the heat transfer on the blade. The winglets reduce the aerodynamic losses by unloading the tip section, reducing the leakage flow rate, turning the leakage flow in a more streamwise direction and reducing the interaction between the leakage fluid and endwall flows. Generally these effects are most effective close to the leading edge of the tip, where the leakage flow is subsonic.

Design, analysis and performance of a polymer-carbon nanotubes based economic solar collector

A low cost flat plate solar collector was developed by using polymeric components as opposed to metal and glass components of traditional flat plate solar collectors. In order to improve the thermal and optical properties of the polymer absorber of the solar collector, Carbon Nanotubes (CNT) were added as a filler. The solar collector was designed as a multi-layer construction with an emphasis on low manufacturing costs. Through the mathematical heat transfer analysis, the thermal performance of the collector and the characteristics of the design parameters were analyzed. Furthermore, the prototypes of the proposed collector were built and tested at a state-of-the-art solar simulator facility to evaluate its actual performance. The inclusion of CNT improved significantly the properties of the polymer absorber. The key design parameters and their effects on the thermal performance were identified via the heat transfer analysis. Based on the experimental and analytical results, the cost-effective polymer-CNT solar collector, which achieved a high thermal efficiency similar to that of a conventional glazed flat plate solar panel, was successfully developed.

Experimental investigation of thermal inertia properties in hemp-lime concrete walls

Hemp-lime concrete is a sustainable alternative to standard building wall materials, with low associated embodied energy. It exhibits good hygric, acoustic and thermal properties, making it an exciting, sustainable building envelope material. When cast in temporary shuttering around a timber frame, it exhibits lower thermal conductivity than concrete, and consequently achieves low U-values in a primarily mono-material wall construction. Although cast relatively thick hemp-lime walls do not generally achieve the low U-values stipulated in building regulations. However assessment of its thermal performance through evaluation of its resistance to thermal transfer alone, underestimates its true thermal quality. The thermal inertia, or reluctance of the wall to change its temperature when exposed to changing environmental temperatures, also has a significant impact on the thermal quality of the wall, the thermal comfort of the interior space and energy consumption due to space heating. With a focus on energy reduction in buildings, regulations emphasise thermal resistance to heat transfer with only less focus on thermal inertia or storage benefits due to thermal mass. This paper investigates dynamic thermal responsiveness in hemp-lime concrete walls. It reports the influence of thermal conductivity, density and specific heat through analysis of steady state and transient heat transfer, in the walls. A novel hot-box design which isolates the conductive heat flow is used, and compared with tests in standard hot-boxes. Thermal diffusivity and effusivity are evaluated, using experimentally measured conductivity, based on analytical relationships. Experimental results evident that hemp-lime exhibits high thermal inertia. They show the thermal inertia characteristics compensate for any limitations in the thermal resistance of the construction material. When viewed together the thermal resistance and mass characteristics of hemp-lime are appropriate to maintain comfortable thermal indoor conditions and low energy operation.

Auditorias energéticas – definição de um plano de ação para edifícios de serviços

O setor dos edifícios representa perto de 40% do consumo de energia final na Europa e cerca de 30% no caso de Portugal [1]. Para fazer face a esta situação foi elaborada e aprovada uma Diretiva Europeia Relativa ao Desempenho Energético dos Edifícios, que foi transposta a nível nacional através de um pacote legislativo assente em três pilares, nomeadamente o Sistema Nacional de Certificação Energética e da Qualidade do Ar Interior (SCE), o Regulamento dos Sistemas Energéticos de Climatização em Edifícios (RSECE) e o Regulamento das Características de Comportamento Térmico dos Edifícios (RCCTE). Atuando ao nível da eficiência energética o consumo de energia nos edifícios pode diminuir para metade, para tal é necessário proceder-se à execução de auditorias energéticas para poder determinar as soluções mais adequadas de forma a reduzir os desperdícios e custos associados ao consumo de energia. Nesta dissertação desenvolveu-se uma metodologia para a realização de auditorias energéticas em edifícios que assenta essencialmente em cinco etapas, nomeadamente: o planeamento, a análise do estado atual, o planeamento estratégico, a elaboração de relatório e a implementação de medidas com acompanhamento de resultados. A aplicação desta metodologia constitui uma grande ajuda na realização de auditorias energéticas conferindo uma maior qualidade à sua execução. De forma a validar a metodologia efetuada foi realizado o estudo de três casos práticos relativos a três agências bancárias (denominadas de A, B e C), em que duas delas pertencem a um projeto de eficiência energética que engloba 50 agências e uma outra que pertence a um outro projeto de apenas 3 agências. A metodologia segue a mesma lógica para as três agências, no entanto, em termos de validação, a última instalação baseia-se nos consumos dos dados monitorizados em contínuo.

Projeto de Térmica: Aplicação do Novo Regulamento de Desempenho Energético dos Edifícios de Habitação Novos

Neste trabalho estudou-se a nova regulamentação de térmica em edifícios, Decreto-Lei nº 118/2013, dando particular ênfase ao Regulamento de Desempenho Energético dos Edifícios de Habitação, REH. Para o efeito, aplicou-se a metodologia definida nesta legislação a um edifício de habitação unifamiliar e compararam-se os resultados obtidos com os resultados da ferramenta de cálculo automático elaborada pelo ITEcons. Fizeram-se ainda várias simulações para as diferentes zonas climáticas possíveis e comparou-se também com o mesmo edifício mas admitindo que todas as soluções construtivas são as de referência.

L’amélioration de la performance et de la structure cardiaque par la moxonidine chez les SHR est accompagnée d’une diminution des cytokines, de la MAPK p38 et de l’Akt

L’hypertrophie du ventricule gauche (HVG) est un processus adaptif et compensatoire qui se développe conséquemment à l’hypertension artérielle pour s’opposer à l’élévation chronique de la pression artérielle. L’HVG est caractérisée par une hypertrophie des cardiomyocytes suite à l’augmentation de la synthèse d’ADN, une prolifération des fibroblastes, une augmentation du dépôt de collagène et une altération de la matrice extracellulaire (MEC). Ces changements génèrent des troubles de relaxation et mènent au dysfonctionnement diastolique, ce qui diminue la performance cardiaque. La suractivité du système nerveux sympathique (SNS) joue un rôle essentiel dans le développement de l’hypertension artérielle et de l’HVG à cause de la libération excessive des catécholamines et de leurs effets sur la sécrétion des cytokines pro-inflammatoires et sur les différentes voies de signalisation hypertrophiques et prolifératives. Le traitement antihypertenseur avec de la moxonidine, un composé sympatholytique d’action centrale, permet une régression de l’HVG suite à une réduction soutenue de la synthèse d'ADN et d’une stimulation transitoire de la fragmentation de l'ADN qui se produit au début du traitement. En raison de l’interaction entre l’HVG, les cytokines inflammatoires, le SNS et leurs effets sur les protéines de signalisation hypertrophiques, l’objectif de cette étude est de détecter dans un modèle animal d’hypertension artérielle et d’HVG, les différentes voies de signalisation associées à la régression de l’HVG et à la performance cardiaque. Des rats spontanément hypertendus (SHR, 12 semaines) ont reçu de la moxonidine à 0, 100 et 400 µg/kg/h, pour une période de 1 et 4 semaines, via des mini-pompes osmotiques implantées d’une façon sous-cutanée. Après 4 semaines de traitement, la performance cardiaque a été mesurée par écho-doppler. Les rats ont ensuite été euthanasiés, le sang a été recueilli pour mesurer les concentrations des cytokines plasmatiques et les cœurs ont été prélevés pour la détermination histologique du dépôt de collagène et de l'expression des protéines de signalisation dans le ventricule gauche. Le traitement de 4 semaines n’a eu aucun effet sur les paramètres systoliques mais a permis d’améliorer les paramètres diastoliques ainsi que la performance cardiaque globale. Par rapport au véhicule, la moxonidine (400 µg/kg/h) a permis d’augmenter transitoirement la concentration plasmatique de l’IL-1β après une semaine et de réduire la masse ventriculaire gauche. De même, on a observé une diminution du dépôt de collagène et des concentrations plasmatiques des cytokines IL-6 et TNF-α, ainsi qu’une diminution de la phosphorylation de p38 et d’Akt dans le ventricule gauche après 1 et 4 semaines de traitement, et cela avec une réduction de la pression artérielle et de la fréquence cardiaque. Fait intéressant, les effets anti-hypertrophiques, anti-fibrotiques et anti-inflammatoires de la moxonidine ont pu être observés avec la dose sous-hypotensive (100 µg/kg/h). Ces résultats suggèrent des effets cardiovasculaires bénéfiques de la moxonidine associés à une amélioration de la performance cardiaque, une régulation de l'inflammation en diminuant les niveaux plasmatiques des cytokines pro-inflammatoires ainsi qu’en inhibant la MAPK p38 et Akt, et nous permettent de suggérer que, outre l'inhibition du SNS, moxonidine peut agir sur des sites périphériques.

Performance of phase change material boards under natural convection

The high thermal storage capacity of phase change material (PCM) can reduce energy consumption in buildings through energy storage and release when combined with renewable energy sources, night cooling, etc. PCM boards can be used to absorb heat gains during daytime and release heat at night. In this paper, the thermal performance of an environmental chamber fitted with phase change material boards has been investigated. During a full-cycle experiment, i.e. charging–releasing cycle, the PCM boards on a wall can reduce the interior wall surface temperature during the charging process, whereas the PCM wall surface temperature is higher than that of the other walls during the heat releasing process. It is found that the heat flux density of the PCM wall in the melting zone is almost twice as large as that of ordinary wall. Also, the heat-insulation performance of a PCM wall is better than that of an ordinary wall during the charging process, while during the heat discharging process, the PCM wall releases more heat energy. The convective heat transfer coefficient of PCM wall surface calculated using equations for a normal wall material produces an underestimation of this coefficient. The high convective heat transfer coefficient for a PCM wall is due to the increased energy exchange between the wall and indoor air.

A simplified method for referring the energy and overheating performance of window design

This paper describes a simplified dynamic thermal model which simulates the energy and overheating performance of windows. To calculate artificial energy use within a room, the model employs the average illuminance method, which takes into account the daylight energy impacting upon the room by the use of hourly climate data. This tool describes the main thermal performance ( heating, cooling and overheating risk) resulting proposed a design of window. The inputs are fewer and simpler than that are required by complicated simulation programmes. The method is suited for the use of architects and engineers at the strategic phase of design, when little is available.

High performance polyester-based materials

Biaxially oriented films produced from semi-crystalline, semi-aromatic polyesters are utilised extensively as components within various applications, including the specialist packaging, flexible electronic and photovoltaic markets. However, the thermal performance of such polyesters, specifically poly(ethylene terephthalate) (PET) and poly(ethylene-2,6-naphthalate) (PEN), is inadequate for several applications that require greater dimensional stability at higher operating temperatures. The work described in this project is therefore primarily focussed upon the copolymerisation of rigid comonomers with PET and PEN, in order to produce novel polyester-based materials that exhibit superior thermomechanical performance, with retention of crystallinity, to achieve biaxial orientation. Rigid biphenyldiimide comonomers were readily incorporated into PEN and poly(butylene-2,6-naphthalate) (PBN) via a melt-polycondensation route. For each copoly(ester-imide) series, retention of semi-crystalline behaviour is observed throughout entire copolymer composition ratios. This phenomenon may be rationalised by cocrystallisation between isomorphic biphenyldiimide and naphthalenedicarboxylate residues, which enables statistically random copolymers to melt-crystallise despite high proportions of imide sub-units being present. In terms of thermal performance, the glass transition temperature, Tg, linearly increases with imide comonomer content for both series. This facilitated the production of several high performance PEN-based biaxially oriented films, which displayed analogous drawing, barrier and optical properties to PEN. Selected PBN copoly(ester-imide)s also possess the ability to either melt-crystallise, or form a mesophase from the isotropic state depending on the applied cooling rate. An equivalent synthetic approach based upon isomorphic comonomer crystallisation was subsequently applied to PET by copolymerisation with rigid diimide and Kevlar®-type amide comonomers, to afford several novel high performance PET-based copoly(ester-imide)s and copoly(ester-amide)s that all exhibited increased Tgs. Retention of crystallinity was achieved in these copolymers by either melt-crystallisation or thermal annealing. The initial production of a semi-crystalline, PET-based biaxially oriented film with a Tg in excess of 100 °C was successful, and this material has obvious scope for further industrial scale-up and process development.

Proper evaluation of the external convective heat transfer for the thermal analysis of cool roofs

Cool materials are characterized by high solar reflectance and high thermal emittance; when applied to the external surface of a roof, they make it possible to limit the amount of solar irradiance absorbed by the roof, and to increase the rate of heat flux emitted by irradiation to the environment, especially during nighttime. However, a roof also releases heat by convection on its external surface; this mechanism is not negligible, and an incorrect evaluation of its entity might introduce significant inaccuracy in the assessment of the thermal performance of a cool roof, in terms of surface temperature and rate of heat flux transferred to the indoors. This issue is particularly relevant in numerical simulations, which are essential in the design stage, therefore it deserves adequate attention. In the present paper, a review of the most common algorithms used for the calculation of the convective heat transfer coefficient due to wind on horizontal building surfaces is presented. Then, with reference to a case study in Italy, the simulated results are compared to the outcomes of a measurement campaign. Hence, the most appropriate algorithms for the convective coefficient are identified, and the errors deriving by an incorrect selection of this coefficient are discussed.