Dissertations / Theses on the topic 'Hygrothermal and energy performance'

Thermal improvement of traditional and historic buildings is going to play a crucial role in the achievement of established carbon emission targets. The suitable retrofit options for traditional buildings are, however, very limited and their long term performance is still uncertain. Evaluation of risks, prior to any alteration of building physics, is critical to avoid future damage to the fabric or occupants’ health. Moisture dynamics in building envelopes are affected by the enclosure’s geometry, materials properties and external and internal boundary conditions. Since the internal boundary is heavily influenced by users, understanding their behaviour is essential to predict the outcome of energy retrofit measures more accurately. The effect of user behaviour on energy demand has been extensively investigated; however, its impact on the hygrothermal performance of the envelopes has barely been explored. This research approached the connection between users and buildings from a new angle looking at the effect that user behaviour has on moisture dynamics of buildings’ envelopes after the retrofit. Qualitative and quantitative research methods were used to develop a holistic evaluation of the question. Firstly, factors influencing the adoption of energy efficiency measures in traditional buildings were explored by means of semi-structured interviews with private owners and project managers. Subsequently, a multi-case study including interviews with occupants and monitoring of environmental conditions was conducted. Data collected at this stage was used to explore users’ daily practices of comfort and to characterise the internal climate of traditional dwellings. Lastly, users’ impact was quantified using Heat, Air and Moisture (HAM) numerical simulation. This allowed for the evaluation of the hygrothermal performance of walls under different internal climate scenarios. Combined results of interviews, environmental monitoring and simulation showed that internal climate can compromise envelope performance after the retrofit and highlighted the need to consider users in the decision making process. Ultimately, the results of this research will help to increase awareness about the potential impact of user behaviour and provide recommendations to decision makers involved in the energy retrofit of traditional structures.

En France, le secteur du bâtiment est le plus grand consommateur d'énergie et représente environ 43% de la consommation totale d'énergie. L'isolation thermique dans le bâtiment est nécessaire afin d'améliorer son efficacité énergétique. Dans certains pays dont la France, la rénovation des bâtiments occupe une place essentielle dans la stratégie de transition énergétique. La stratégie mise en place consiste donc à renforcer l'isolation thermique des enveloppes de bâtiment et ceci en perdant le moins de surface habitable possible. Ceci justifie le fait de développer et de mettre en œuvre à l'avenir des matériaux super isolants comme les aérogels. Les objectifs de cette étude sont d'examiner le comportement thermique des bâtiments et d'étudier l'amélioration possible de leur efficacité énergétique en utilisant un nouvel enduit isolant à base d'aérogels de silice et ainsi que l'énergie solaire. Tout d'abord, la performance thermique et hygrothermique des murs extérieurs est étudiée afin de trouver la meilleure structure de ces murs. Deuxièmement, nous étudions l'évolution du confort thermique et du comportement énergétique des maisons en adoptant le nouvel enduit isolant comme isolation extérieure. Cette évolution a aussi été représentée par un modèle mathématique. On a comparé les résultats obtenus à l'aide de ces modèles avec les mesures expérimentales faites sur une maison récemment construite. Enfin, le potentiel de réduction de la charge de chauffage en adoptant un système actif dans la paroi est analysé. Ce système est proposé pour capter une partie de l'énergie solaire qui tombe sur la façade sud et qui est disponible pendant les journées non nuageuses en hiver, et la transférer vers la façade nord par l'intermédiaire de canalisations d'eau intégrées dans l'enduit isolant objet de l'étude
In France, the building sector is the largest consumer of energy and accounts for about 43% of the total energy consumption. The building sector offers significant potential for improved energy efficiency through the use of high-performance insulation and energy-efficient systems. For existing buildings, renovation has a high priority in France because these buildings represent a high proportion of energy consumption and they will be present for decades to come. Nowadays, there is a growing interest in the so-called super-insulating materials, such as Aerogels. The objectives of this study are to examine the thermal behavior of buildings and to foster energy efficiency through the use of a newly developed aerogel-based insulating coating as well as the use of renewable energy sources, specifically solar energy. Firstly, the thermal and hygrothermal performance of exterior walls having different layer composition structures are examined. Secondly, the heating energy demand as well as the risk of summer overheating is examined for different construction periods and under different climates. Also, a mathematical model is built and compared to experimental measurement of a recently built full-scale house. Finally, the potential to decrease the heating load by adopting a closed wall loop system is scrutinized. The latter is a proposed system to capture some of the solar energy falling on the south facade available during non-cloudy winter days and transfer it to the north facade through water pipes embedded in the aerogel-based coating

This study focuses on the hygrothermal performance of Moso bamboo. The knowledge in this aspect is remarkable important for the research of building energy saving and the low carbon building design. However, the detailed hygrothermal properties of Moso bamboo are fairly rare. To obtain these data, a series of experimental works have been done for measurement of density, porosity, thermal conductivity, specific heat capacity, water vapour permeability, hygrothermal expansion and sorption isotherm of Moso bamboo. To obtain further understanding on the hygrothermal performance of Moso bamboo, a number of dynamic heat and moisture transfer experiments were conducted. These experiments simulated two extreme outdoor environments and one indoor environment. The temperature and RH responses of Moso bamboo panels were monitored. Then a coupled transient heat and moisture transfer numerical simulation at the material level was conducted to predict and validate the hygrothermal performance of Moso bamboo. A sensitivity study of the hygrothermal properties of bamboo was also presented to indentify the influence of each hygrothermal property of Moso bamboo. Major findings include the following aspects. Both experiment and simulation results appear to be consistent with the results of measurements of the basic hygrothermal parameters. The parametric study found that density can be regarded as the most sensible parameter to influence the temperature simulation results at the transient state, while the thermal conductivity dominated the temperature variation at the steady state. The water vapour diffusion resistance factor can be regarded as the most critical parameter to influence the RH simulation results. The influence of liquid water diffusivity is negligible in this study. The parametric study results indicated that the simulation with moisture is more accurate than the simulation without moisture in both equilibrium and transient state. The results also imply that the existence of moisture could increase the heat capacity and reduce the thermal conductivity. The results of this study recommend that the external part of the bamboo culm wall can be utilised to minimise the RH variation of the panel while the internal part of the bamboo culm wall is suitable to increase the thermal insulation performance of the panel. To avoid hygroexpansion, the implementation of external part of bamboo culm wall needs to be minimised.

The static and fatigue properties of advanced epoxy-based composites reinforced with carbon, glass or aromatic polyamide (Kevlar-49) fibres have been measured for a range of different loading and environmental conditions. Cross-plied laminates were tested in tension in the 0/90 and +/-45° orientations and also under flexural loading. The laminates were similar, except for the type of fibre. The effects of environmental exposure were assessed by preconditioning test specimens to equilibrium by either drying at 60°C, storage at 65%RH at ambient temperature or boiling in water. Moisture absorption was through the resin alone for CFRP and GRP and by additional absorption by the fibres for KFRP. Fatigue testing revealed that the tensile performance in the 0/90 orientation is strongly dependent on the level of cyclic strain. 0/90 CFRP has excellent fatigue and environmental resistance but GRP exhibits a steep fatigue curve and the static and low cycle fatigue strengths are both reduced by boiling. The fatigue strength of 0/90 KFRP is reduced by drying, more so than by boiling, and in all conditions the stress/log-life curves are characterised by a downward curvature or 'knee'. Tensile preloads do not significantly affect the residual fatigue properties or the equilibrium levels of moisture uptake, although extensive damage involving cracking in both longitudinal and transverse plies may lead to increased absorption rates. A tendency for Kevlar fibres to split or 'defibrillate' plays an important role in most failures of KFRP. It limits the shear strength and causes flexural failures to occur at the compression surface at low stress levels. 0/90 CFRP also fails at the compression surface in flexure but GRP fails at the tensile surface, the environmental fatigue performance resembling that under axial tensile loading. The +/-45° tensile and low cycle fatigue strengths are sensitive to the effects of conditioning, all laminates exhibiting optimum performance after conditioning at 65%RH, although generally these effects become insignificant at long lives.

This thesis explores the hygrothermal performance of hemp insulation in the context of the United Kingdom. The key objectives of this investigation were to assess the heat and moisture management capacities of hemp insulations in two constructions typical to the UK, of timber frame and solid brick walls and to put the findings of the assessment into the greater context of conventional insulation materials by comparing hemp insulation’s performance with that of stone wool. The assessments were performed by means of laboratory-based experiments, in situ experimental monitoring and computer based numerical hygrothermal simulations. The most important finding during the laboratory-based experiment is that, in high relative humidity, the likelihood and frequency of interstitial condensation is higher in stone wool insulation than in hemp insulation. In terms of the material properties, one of the key findings during the laboratory-based experiment is the high level of moisture buffering capacities of hemp insulations, and therefore their potential in managing moisture in buildings. The in situ assessment of hygrothermal properties of hemp and stone wool insulations confirms the findings of the laboratory based experiments of the corresponding moisture management capacities of these two insulation materials. Parametric analysis of the in situ data shows that mould spore germination is possible in the insulations in vapour open walls although the visual observation has not confirmed the outcome of this analysis. In terms of thermal conductivity, the important finding is that the equivalent thermal conductivity of hemp and stone wool insulations are always equal or below the manufacturers’ declared thermal conductivity values. Long-term hygrothermal performances of hemp and stone wool insulation in timber frame and solid brick walls have been also assessed using a numerical hygrothermal simulation tool (WUFI). As far as the WUFI predictions are concerned, the application of the hemp or stone wool insulation on solid brick wall does not seem to be feasible with reference to condensation and mould growth in the insulations.

The need for efficient, sustainable, and planned utilization of resources is ever more critical. In the U.S. alone, buildings consume 34.8 Quadrillion (1015) BTU of energy annually at a cost of $1.4 Trillion. Of this energy 58% is utilized for heating and air conditioning. Several building energy analysis tools have been developed to assess energy demands and lifecycle energy costs in buildings. Such analyses are also essential for an efficient HVAC design that overcomes the pitfalls of an under/over-designed system. DOE-2 is among the most widely known full building energy analysis models. It also constitutes the simulation engine of other prominent software such as eQUEST, EnergyPro, PowerDOE. Therefore, it is essential that DOE-2 energy simulations be characterized by high accuracy. Infiltration is an uncontrolled process through which outside air leaks into a building. Studies have estimated infiltration to account for up to 50% of a building’s energy demand. This, considered alongside the annual cost of buildings energy consumption, reveals the costs of air infiltration. It also stresses the need that prominent building energy simulation engines accurately account for its impact. In this research the relative accuracy of current air infiltration calculation methods is evaluated against an intricate Multiphysics Hygrothermal CFD building envelope analysis. The full-scale CFD analysis is based on a meticulous representation of cracking in building envelopes and on real-life conditions. The research found that even the most advanced current infiltration methods, including in DOE-2, are at up to 96.13% relative error versus CFD analysis. An Enhanced Model for Combined Heat and Air Infiltration Simulation was developed. The model resulted in 91.6% improvement in relative accuracy over current models. It reduces error versus CFD analysis to less than 4.5% while requiring less than 1% of the time required for such a complex hygrothermal analysis. The algorithm used in our model was demonstrated to be easy to integrate into DOE-2 and other engines as a standalone method for evaluating infiltration heat loads. This will vastly increase the accuracy of such simulation engines while maintaining their speed and ease of use characteristics that make them very widely used in building design.

Energy Performance Contracting is an energy saving method, when the supplier guarantees a certain minimal level of energy savings to the customer, as well as non-rising energy costs. The method was developed at the turn of 70's and 80's in the USA and has spread to dozens of countries around the world till today, although the rate of the EPC market development differs from country to country. The method is useful mostly for heating, electricity and gas cost savings by the end-users. In the Czech Republic, the method has been used since 1993. Until now, several dozens, or even hundreds of projects have been realized, mostly for public sector customers. This paper analyzes the current state of the EPC method usage around the world as well as in the Czech Republic, the key part comprises of the EPC principles description, based on data from real EPC contracts. The work is concluded by a SWOT analysis of the method and by a discussion of the following question: "Can EPC projects blockade the overall saving potential in some cases?" The key information source for most of the work were answers to questions sent to eight Czech ESCO companies representatives, as well as the outputs from guided interviews with four of them, which were taking place between January and May 2009.

Les économies d'énergie et la réduction des émissions des gaz à effet de serre dans le secteur du bâtiments ainsi que le maintien d’un confort hygrométrique prennent une importance majeur ces dernières décennies. L'utilisation de matériaux à changement de phase (MCP) ou de matériaux hygroscopiques d'origine végétale pour l'enveloppe des bâtiments est une solution prometteuse. Les MCP conduit à améliorer le confort thermique intérieur et à réduire la consommation d'énergie, tandis que les matériaux hygroscopiques biosourcés sont des matériaux respectueux de l'environnement et permettent la régulation de l'humidité intérieure et assure une isolation thermique optimale. Cependant, seules quelques études ont exploré l'application l’intégration de ces deux types de matériaux et analysé de manière exhaustive les performances énergétiques et hygrothermiques. Cette thèse propose une solution d'enveloppe passive qui intègre le PCM et le béton de chanvre biosourcé pour améliorer simultanément les performances énergétiques, et hygrothermiques du bâtiment. Les principaux objectifs de cette étude sont d'examiner la faisabilité des enveloppes intégrées, d'étudier de manière exhaustive les performances hygrothermiques et énergétiques ainsi que les avantages et les inconvénients de différentes configurations avec le PCM placé à différents endroits du béton de chanvre.Tout d'abord, des expériences ont été menées en comparant les performances hygrothermiques d'une enveloppe de référence (béton de chanvre uniquement) et de trois enveloppes intégrées avec du MCP placé à différents endroits dans deux conditions limites typiques. Les résultats ont montré la faisabilité des enveloppes intégrées. La présence de PCM a augmenté les inerties thermique et hygrique de l'enveloppe. Par conséquent, le déphasage a été augmenté et l'amplitude de la température et de l'humidité relative a été réduite. Les différentes configurations présentaient des avantages et des inconvénients différents. La configuration dans laquelle le MCP est placé au milieu du béton de chanvre est intéressante car elle présente une faible fluctuation et un dephasage interessant à la fois pour les variations de la température et de l'humidité relative, et conduit ainsi à de grandes économies d'énergie.Ensuite, le modèle physique i, de transfert de la chaleur et de l’humidité, à l’échelle de l'enveloppe a été développé. Ce modèle intègre la dépendance de la température et de la caractéristique hygroscopique du béton de chanvre. La précision du modèle a été validée par comparaison avec les données expérimentales. Sur la base du modèle validé, les simulations ont été effectuées dans un climat méditerranéen afin d'étudier de manière exhaustive les performances hygrothermiques et énergétiques de l'enveloppe intégrée. Les résultats ont mis en évidence le rôle indispensable du transfert d'humidité dans la détermination de la charge hugrothermique, ainsi que l'effet précieux de l'enveloppe sur l'amélioration des performances énergétiques et hygrothermiques. En outre, l'enveloppe intégrée avec le PCM proche de (mais pas en contact avec) l'intérieur a montré un grand potentiel pour économiser de l'énergie et s'adapter aux variations d'humidité du climat tout en garantissant l'équilibre de l'humidité dans le béton de chanvre. Enfin, l'analyse paramétrique a été réalisée du point de vue des propriétés du MCP (épaisseur, chaleur latente et plage de transition de phase), et le risque d'application (condensation et développement de moisissures) a été évalué. Les résultats de l'analyse paramétrique ont montré que les performances de l'enveloppe pouvaient être améliorées en augmentant l'épaisseur et la chaleur latente de MCP et en identifiant la plage de transition de phase appropriée du MCP. Les résultats de l'évaluation des risques ont confirmé que l'enveloppe ne présentait aucun risque de condensation et de développement de moisissures
With the development of society, the demand for energy saving and carbon emission reduction in buildings as well as the indoor thermal and humidity environment comfort is gradually increasing. Using Phase change materials (PCMs) or bio-based hygroscopic materials as building envelopes are promising solutions. PCMs can improve indoor thermal comfort and reduce energy consumption, while bio-based hygroscopic materials are environment-friendly materials that enable indoor humidity regulation and thermal insulation. However, only a few studies have explored the integrated application of the two types of materials and comprehensively analyzed the energy and hygrothermal performance. This dissertation proposed a passive envelope solution that integrates PCM and bio-based hemp concrete (HC) to simultaneously improve the energy, thermal, and hygric performances of buildings. The main objectives of this study are to investigate the feasibility of the integrated envelopes, to comprehensively study the hygrothermal and energy performance as well as the advantages and disadvantages of different configurations with PCM placed in different locations of the HC, and to conduct the parametric analysis and evaluate the application risks of the integrated envelope.First, experiments were conducted by comparing the hygrothermal performance of a reference envelope (HC only) and three integrated envelopes with PCM placed in different locations under two typical boundary conditions. The results demonstrated the feasibility of the integrated envelopes. The presence of PCM increased the thermal and hygric inertia of the envelope. As a result, the time delay was increased and the temperature/relative humidity amplitude was decreased. Different configurations had different advantages and disadvantages. The configurations with PCM placed in the middle of the HC was worth noting as it had small temperature/relative humidity fluctuation, long temperature time delay, and large energy savings.Then, the mathematical model of the integrated envelope that couples heat and moisture transfer and considers the temperature dependence of HC’s hygroscopic characteristic was developed. The accuracy of the model was validated by comparison with the experimental data. Based on the validated model, the simulations were performed in a Mediterranean climate to comprehensively investigate the hygrothermal and energy performance of the integrated envelope. The results highlighted the indispensable role moisture transfer plays in determining the indoor hygric environment and heat load, as well as the valuable effect of the integrated envelope on improving both energy and hygrothermal performance. Besides, the integrated envelope with PCM close to (but not in contact with) the interior showed great potential for saving energy and adapting to climate humidity variation while guaranteeing moisture equilibrium within the HC.Finally, the parametric analysis was performed from the perspective of PCM properties (thickness, latent heat, and phase transition range), and the application (condensation and mold growth) risk was evaluated. The results of the parametric analysis illustrated that the performance of the integrated envelope could be improved by increasing the thickness and latent heat and identifying the appropriate phase transition range of the PCM. The risk evaluation results confirmed that the integrated envelope was free from the risk of condensation and mold growth

Advances in processor design have delivered performance improvements for decades. As physical limits are reached, however, refinements to the same basic technologies are beginning to yield diminishing returns. Unsustainable increases in energy consumption are forcing hardware manufacturers to prioritise energy efficiency in their designs. Research suggests that software modifications will be needed to exploit the resulting improvements in current and future hardware. New tools are required to capitalise on this new class of optimisation. This thesis investigates the field of energy-aware performance engineering. It begins by examining the current state of the art, which is characterised by ad-hoc techniques and a lack of standardised metrics. Work in this thesis addresses these deficiencies and lays stable foundations for others to build on. The first contribution made includes a set of criteria which define the properties that energy-aware optimisation metrics should exhibit. These criteria show that current metrics cannot meaningfully assess the utility of code or correctly guide its optimisation. New metrics are proposed to address these issues, and theoretical and empirical proofs of their advantages are given. This thesis then presents the Power Optimised Software Envelope (POSE) model, which allows developers to assess whether power optimisation is worth pursuing for their applications. POSE is used to study the optimisation characteristics of codes from the Mantevo mini-application suite running on a Haswell-based cluster. The results obtained show that of these codes TeaLeaf has the most scope for power optimisation while PathFinder has the least. Finally, POSE modelling techniques are extended to evaluate the system-wide scope for energy-aware performance optimisation. System Summary POSE allows developers to assess the scope a system has for energy-aware software optimisation independent of the code being run.

In many studies efforts are made to decrease the energy consumption of trains by optimizing their drive style, e.g. accelerate and brake optimally and regenerate electricity when braking. In other studies the goal is to distribute the run time between stations in an optimal way to decrease the energy consumption, given a relatively simple drive style. In this report the goal is to combine these two energy saving methods to obtain as low energy consumption as possible. By coupling one software containing a drive style optimizer with another software which by different optimization methods calculates the optimal run time distribution on a given track this is accomplished. The study also contains a comparison between drive styles, with the goal to find a relatively simple but energy efficient drive style. Finally the dependence between run time distribution and energy consumption is further analysed. The results show that by redistributing the run times the energy consumption can be decreased compared to previously existing time tables. They also show that a relatively simple drive style gives comparable energy consumption compared to the one obtained using a drive style optimizer. Finally the results show that the dependence between run time and energy consumption can be approximated with a simple second order equation.

In this dissertation, the effect of temperature and humidity on the viscoelastic and fracture properties of proton exchange membranes (PEM) used in fuel cell applications was studied. Understanding and accurately modeling the linear and nonlinear viscoelastic constitutive properties of a PEM are important for making hygrothermal stress predictions in the cyclic temperature and humidity environment of operating fuel cells. In this study, Nafion® NRE 211, Gore-Select® 57, and Ion Power® N111-IP were characterized under various humidity and temperature conditions. These membranes were subjected to a nominal strain in a dynamic mechanical analyzer (DMA), and their stress relaxation behavior was characterized over a period of time. Hygral master curves were constructed noting hygral shift factors, followed by thermal shifts to construct a hygrothermal master curve. This process was reversed (thermal shifts followed by hygral shifts) and was seen to yield a similar hygrothermal master curve. Longer term stress relaxation tests were conducted to validate the hygrothermal master curve. The Prony series coefficients determined based on the hygrothermal stress relaxation master curves were utilized in a linear viscoelastic stress model. The nonlinear viscoelastic behavior of the membranes was characterized by conducting creep tests on uniaxial tensile specimens at various constant stress conditions and evaluating the resulting isochronal stress-strain plots. The nonlinearity was found to be induced at relatively moderate stress/strain levels under dry conditions. To capture the nonlinearity, the well known Schapery model was used. To calculate the nonlinear parameters defined in the Schapery model, creep/recovery tests at various stress levels and temperatures were performed. A one-dimensional Schapery model was developed and then validated using various experiments. The fracture properties were studied by cutting membranes using a sharp knife mounted on a specially designed fixture. Again, various temperature and humidity conditions were used, and the fracture energy of the membranes was recorded as a function of cutting rate. Fracture energy master curves with respect to reduced cutting rates were constructed to get some idea about the intrinsic fracture energy of the membrane. The shift factors obtained from the fracture tests were found to match with those obtained from the stress relaxation experiments, suggesting that the knife cutting process is viscoelastic in nature. The rate and temperature dependence for these fracture energies are consistent with the rate, temperature, and moisture dependence of the relaxation modulus, suggesting the usefulness of a viscoelastic framework for examining and modeling durability of fuel cell membranes. The intrinsic fracture energy was initially thought to be a differentiating factor, which would separate various membranes tested in this study from one another. However, it was later found that all the membranes tested showed similar values at lower cutting rates, but showed significant variation at higher reduced cutting rates, and thus was thought to be a more meaningful region to differentiate the membranes for durability understanding. While the preceding work was undertaken to characterize as-received commercial PEMs, it is possible to modify material properties through treatment processes including thermal annealing and water treatment. The transient and dynamic viscoelastic properties of water-treated Nafion membranes revealed unusual behavior. Such unusual properties might have originated from irreversible morphological changes in PEM. Besides the constitutive viscoelastic properties, another set of properties useful for the stress modeling is the hygral strain induced as a function of relative humidity (RH) The effect of pretreatment on hygral strains induced as a function of RH was also investigated. These studies suggest that pretreatment significantly changes the mechanical properties of proton exchange membranes.
Ph. D.

Recentemente foram aprovadas normas para requisitos e critérios de desempenho térmico de habitações de interesse social. Estas normas são importantes para a melhoria do desempenho térmico dessas habitações no Brasil. No entanto, a abordagem adotada é geral no que diz respeito às regiões bioclimáticas brasileiras e a análise é feita para sistemas da edificação (aberturas, paredes, cobertura) isoladamente, o que pode não expressar o comportamento térmico para determinadas condições climáticas. O presente estudo apresenta uma proposta de método de avaliação de desempenho higrotérmico de habitações térreas unifamiliares de interesse social para condições climáticas de Porto Alegre, RS, que visa à avaliação global da edificação através de requisitos e critérios que complementam aqueles propostos pelas normas e que sejam de fácil aplicação pelos envolvidos no processo de produção de habitações de interesse social. Considera-se a possibilidade de condensação sobre superfícies internas da edificação, coeficientes volumétricos globais de perda e ganho de calor através de sua envolvente, inércia térmica, entre outros, obtidos da literatura e da análise de quatro habitações construídas em Porto Alegre, duas submetidas a medições in loco e duas consideradas como referência para habitação de interesse social para as condições econômicas e culturais do público-alvo, segundo agentes ligados ao setor em Porto Alegre. O método foi submetido à opinião de agentes, envolvidos com o financiamento, projeto, execução, fiscalização e avaliação de habitações de interesse social em Porto Alegre, e a especialistas da área de conforto térmico atuando em instituições de ensino e pesquisa nacionais. São indicados três graus de qualidade que podem ser atingidos pelas habitações, de acordo com a disponibilidade de recursos para a construção da habitação. O método pode ser uma ferramenta auxiliar na tomada de decisão no processo de projeto, aprovação e avaliação de habitações de interesse social pelos agentes públicos ligados ao setor.
Recently, low cost housing thermal performance standards were developed and approved in Brazil. These standards establish requirements and criteria that low cost housing must satisfy. However, the approach used generally deals with climatic conditions and the evaluation is based on analysis of individual components. This approach cannot express the real thermal behaviour of housing. This study presents a thermal performance evaluation method for low cost single-family one-floor housing considering the climatic conditions of Porto Alegre, Brazil. The method aims toward a global evaluation of housing through requirements and criteria that complement the standards approved recently and it considers mathematical procedures that can be easily applied by government agents involved in this task. Inner surface condensation, global flow heat coefficients, thermal inertia, among others, obtained from literature, are proposed. Four low cost houses built in Porto Alegre, considered to be references according to social and economic local reality, were evaluated through the method. Government agents involved in the project, design, financing, building, overseeing and evaluation of low cost housing in Porto Alegre and experts from research institutes in Brazil also gave their opinions of the method. Three degrees of performance for housing, in accordance with availability of government resources, are defined. The method can be used as an evaluation of possible solutions, thereby aiding decision makers.

Geothermal energy is an important source of clean and renewable energy. This project deals with the study of deep geothermal power plants for the generation of electricity. The design involves the extraction of heat from the Earth and its conversion into electricity. This is performed by allowing fluid deep into the Earth where it gets heated due to the surrounding rock. The fluid gets vaporized and returns to the surface in a heat pipe. Finally, the energy of the fluid is converted into electricity using turbine or organic rankine cycle (ORC). The main feature of the system is the employment of side channels to increase the amount of thermal energy extracted. A finite difference computer model is developed to solve the heat transport equation. The numerical model was employed to evaluate the performance of the design. The major goal was to optimize the output power as a function of parameters such as thermal diffusivity of the rock, depth of the main well, number and length of lateral channels. The sustainable lifetime of the system for a target output power of 2 MW has been calculated for deep geothermal systems with drilling depths of 8000 and 10000 meters, and a financial analysis has been performed to evaluate the economic feasibility of the system for a practical range of geothermal parameters. Results show promising an outlook for deep geothermal systems for practical applications.

The size and capacity of datacenters has grown over time, and today, datacentershave become a significant source for compute capacity. This is because the type, aswell as the number of applications and users that are moving into the cloud have beensteadily increasing. As datacenter use increases, so does the energy consumed bythese large computing facilities. Therefore, by improving datacenter efficiency, one cansignificantly reduce datacenter cost.In order to achieve improved datacenter efficiency, the hardware and softwarebottlenecks that exists in today's software need to be identified and evaluated. In thiswork a number of popular datacenter workloads using the Top-Down methodologywas evaluated with the aim to use it to better understand the bottlenecks andbehavior of these workloads. The goal of this work is to determine if the applicationsshow any time-varying behavior and if there are any potential for improvements ofthe hardware with respect to energy efficiency. The proposed methodology workswell for understanding high level bottlenecks on modern hardware. We identifiedtime-varying behavior as well as areas of improvement common to several studiedapplications.

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O alto consumo de energia dos centros de dados tem sido foco na maioria das pesquisas recentes. Em ambientes de nuvem, v?rias solu??es est?o sendo propostas com o objetivo de alcan?ar efici?ncia energ?tica, que v?o desde o dimensionamento da frequ?ncia de processadores, da utiliza??o de estados suspens?o, at? a consolida??o de servidores virtuais. Embora estas solu??es permitam redu??o no consumo de energia, apresentam impacto sobre o desempenho das aplica??es. Visando resolver esta limita??o, n?s apresentamos uma orquestra??o de diferentes t?cnicas e mecanismos de economia de energia, com a finalidade de melhorar o balanceamento entre economia de energia e desempenho das aplica??es. Para este fim, implementamos o e-eco, um sistema de gest?o que atua juntamente com a plataforma de nuvem, decidindo qual estado de suspens?o pode ser melhor aplicado sobre os servidores, al?m de escolher a melhor op??o entre consolida??o de servidores ou dimensionamento de frequ?ncia dos processadores. Para avaliar o e-eco, testes foram realizados em ambientes de nuvem real e simulado, utilizando aplica??es scale-out em uma infraestrutura de nuvem din?mica, levando em considera??o transa??es-por-segundo como m?trica de desempenho. Os resultados mostraram que nossa proposta apresenta a melhor rela??o entre economia de energia e desempenho de aplica??es em ambientes de nuvem, quando comparada com outros trabalhos apresentados na literatura.
The high energy consumption of data centers has been a recurring issue in recent research. In cloud environments, several solutions are being used that aim for energy efficiency, ranging from scaling the processors frequency, through the use of sleep states, to virtual machine placement mechanism. Although these solutions enable the reduction in power consumption, they usually impact on the application performance. To address this limitation, we present an orchestration of different energy-savings techniques and mechanisms to improve the trade-off between energy savings and application performance. To this end, we implemented the Energy-Efficient Cloud Orchestrator ? e-eco ? a management system that acts along with the cloud platform, deciding which sleep state can be better applied on hosts, in addition to choosing the best option between virtual machines consolidation and dynamic processor frequency scaling. To evaluate e-eco, tests were carried out in a real and a simulated environment using scale-out applications on a dynamic cloud infrastructure, taking into account transactions per second as a performance metric. Results showed that our proposal presents the best improvement on the trade-off between energy savings and performance applications for cloud environments when compared with other works presented in the literature.

The objective of this research was to gain insight into the key drivers of productive organisational energy and to determine whether there is a relationship between productive organisational energy and high performance in organisations. This study also aimed to identify key measures of success of organisations. Organisational energy has a critical role to play in driving both people behaviour and innovation in organisations, ultimately providing a competitive advantage.Both a quantitative and qualitative analysis was conducted on the data collected from four case study organisations, comprising a total sample size of 47 respondents. The research consisted of three phases. Phase One, which made use of an open-ended qualitative survey, was directed at industry experts who were required to identify and recommend four small- to medium- sized high-energy information technology organisations to be considered for this research. Phase Two consisted of gaining approval to conduct research within four of the recommended case study organisations, and conducting an open-ended exploratory face-to-face interview with each Managing Director, with the objective of determining the success, energy state, key drivers, and performance measures of the organisations, as well as the factors that drive the energy of staff. Furthermore, each Managing Director completed the same self-administered questionnaire that formed the basis of Phase Three. This structured survey was used to gather the perceptions and opinions of each organisation’s staff members in determining: the energy state of the organisation, the key drivers of organisational energy, and the link between organisation energy and performance. Statistical analysis techniques were used to determine whether significant relationships exist between the drivers of organisational energy and their respective rankings; and between organisational energy and organisational performance.The study provided evidence that intrapreneurial orientation, collective identity, employee investment and leadership are the most significant drivers of productive organisational energy and confirmed the existence of a significant relationship between productive organisational energy and high performance organisations. Through this research, a model has been developed that can be utilised by leaders of organisations to leverage organisational energy in order to improve and measure organisational performance, thereby creating a sustainable competitive advantage.
Dissertation (MBA)--University of Pretoria, 2012.
Gordon Institute of Business Science (GIBS)
unrestricted

Distributed sensor networks have been discussed for more than 30 years, but the vision of Wireless Sensor Networks (WSNs) has been brought into reality only by the rapid advancements in the areas of sensor design, information technologies, and wireless networks that have paved the way for the proliferation of WSNs. The unique characteristics of sensor networks introduce new challenges, amongst which prolonging the sensor lifetime is the most important. Energy-efficient solutions are required for each aspect of WSN design to deliver the potential advantages of the WSN phenomenon, hence in both existing and future solutions for WSNs, energy efficiency is a grand challenge. The main contribution of this thesis is to present an approach considering the collaborative nature of WSNs and its correlation characteristics, providing a tool which considers issues from physical to application layer together as entities to enable the framework which facilitates the performance evaluation of WSNs. The simulation approach considered provides a clear separation of concerns amongst software architecture of the applications, the hardware configuration and the WSN deployment unlike the existing tools for evaluation. The reuse of models across projects and organizations is also promoted while realistic WSN lifetime estimations and performance evaluations are possible in attempts of improving performance and maximizing the lifetime of the network. In this study, simulations are carried out with careful assumptions for various layers taking into account the real time characteristics of WSN. The sensitivity of WSN systems are mainly due to their fragile nature when energy consumption is considered. The case studies presented demonstrate the importance of various parameters considered in this study. Simulation-based studies are presented, taking into account the realistic settings from each layer of the protocol stack. Physical environment is considered as well. The performance of the layered protocol stack in realistic settings reveals several important interactions between different layers. These interactions are especially important for the design of WSNs in terms of maximizing the lifetime of the network.

Det är nödvändigt för stora företag att förstå och kunna anpassa sig till den industriella omvandling mot ett ökat fokus på energieffektivitet som sker idag. Energieffektiviseringsdirektivet som Europeiska Unionen har utfärdat har ökat fokus på att arbeta med energieffektivitet i stora företag. Vidare har den svenska regeringen infört lagen om energikartläggning i stora företag som är baserad på Energieffektiviseringsdirektivet. Dessa lagstadgade krav uppmuntrar företag att utveckla ett ledningssystem som ställer krav på genomförande av energikartläggningar samt föreslå kostnadseffektiva åtgärder. Energieffektivitet är redan en riktigdel i många företags miljöarbete dock krävs ett mer Utvecklat och systematiskt arbetssätt än det många företag redan har för att uppnå kraven i Energieffektiviseringsdirektivet och den svenska lagen. Företaget som har undersökts i denna studie är ett världsledande teknikföretag med mer än 9000 anställda i Sverige. För närvarande har de energi som en signifikant aspekt i sitt miljöarbete i enlighet med den internationella standarden för miljöledningssystem ISO14001dag utvecklar de även sitt energiarbete genom att utföra energikartläggningar för att uppfylla den nya lagstiftningen. Detta ger en mer detaljerad insikt över energianvändningen och möjliga förbättringar som kan göras, men för att säkerställa ständiga förbättringar över en längre tidsperiod krävs ytterligare åtgärder.  I den här studien har det undersökts vilka åtgärder som ett stort företag måste införa för att öka energiprestandan och följa lagstiftningen. Genom en litteraturstudie som fokuserade på ledningssystem i kombination med intervjuer på det undersöka företaget, en kompletterande studie av två företag som omfattas av direktivet samt tre expertintervjuer identifierades fem nyckelfaktorer. Dessa faktorer är högsta ledningens engagemang, medvetenhet, mål, mätningar och utvärdering. En modell för att strukturera faktorerna utvecklades sedan. Vidare presenterades konkreta förslag på hur dessa faktorer ska implementeras. Genom att öka fokus på dessa nyckelfaktorer och implementera föreslagna åtgärder kommer företag öka sin energiprestanda och medvetenhet i organisationen om hur olika handlingar påverkar företagets energiprestanda.
It is necessary for large companies to understand and be able to adapt to the industrial Transformation towards an increasing focus on energy efficiency, which takes place today. The Energy Efficiency Directive (EED)issued by the European Union has enlarged the focus on working with energy efficiency within large companies. Further, the Swedish government has introduced the law about energy auditing in large companies, which is based on the EED. These regulations encourage companies to develop a management system that includes requirements on conducting energy audits and propose cost Deffective measures. Energy efficiency is already an important aspect within many companies environmental work, however a more developed and systematic approach to energy efficiency than most companies already have is needed in order to fulfill the legal requirements. The Company investigated in this study is one the worlds leading technology companies with more than 9000  employees in Sweden. Currently, they have energy as a significant aspect in their environmental work according to the international management system standard ISO 14001. Today they are also developing their energy work by conducting energy audits in order to comply with the new legislation. This gives a mor detailed view of the energy use and potential improvements that can be done, but in order to ensure continual improvements over a long period of time further measures are needed. Within this study it was investigated what measures a large company needs to implement in order to increase their energy performance and comply with the legislation. By a literature review focusing on management systems as well as interviews within the Company, a complementary study with two companies covered by the EED and three expert  interviews, five key factors were identified. These factors are, top management commitment, awareness, goals, measurements and evaluation. A model was then developed aligning these factors. Further, concrete proposals for action to manage these factors were presented. By!increasing focus on these key factors and implement proposed measures companies will increase their energy performance and also make the organization aware of how actions affect a company’s energy performance

It! is! necessary! for! large! companies! to! understand! and! be! able! to! adapt! to! the! industrial! transformation! towards! an! increasing! focus! on! energy! efficiency,! which! takes! place! today.! The!Energy!Efficiency!Directive!(EED)!issued!by!the!European!Union!has!enlarged!the!focus! on! working! with! energy! efficiency! within! large! companies.! Further,! the! Swedish! government! has! introduced! the! law! about! energy! auditing! in! large! companies,! which! is! based! on! the! EED.! These! regulations! encourage! companies! to! develop! a! management! system!that!includes!requirements!on!conducting!energy!audits!and!propose!costDeffective! measures.! ! Energy! efficiency! is! already! an! important! aspect! within! many! companies! environmental! work,! however! a! more! developed! and! systematic! approach! to! energy! efficiency! than! most! companies! already! have! is! needed! in! order! to! fulfill! the! legal! requirements.! The! Company! investigated! in! this! study! is! one! the! worlds! leading! technology! companies! with! more! than! 9000! employees! in! Sweden.! Currently,! they! have! energy! as! a! significant! aspect! in! their! environmental! work! according! to! the! international! management! system! standard! ISO! 14001.! Today! they! are! also! developing! their! energy! work! by! conducting! energy! audits! in! order!to!comply!with!the!new!legislation.!This!gives!a!more!detailed!view!of!the!energy!use! and! potential! improvements! that! can! be! done,! but! in! order! to! ensure! continual! improvements!over!a!long!period!of!time!further!measures!are!needed.!! ! Within! this! study! it! was! investigated! what! measures! a! large! company! needs! to! implement! in! order! to! increase! their! energy! performance! and! comply! with! the! legislation.! By! a! literature! review! focusing! on! management! systems! as! well! as! interviews! within! the! Company,! a! complementary! study! with! two! companies! covered! by! the! EED! and! three! expert! interviews,! five! key! factors! were! identified.! These! factors! are;! top! management! commitment,! awareness,! goals,! measurements! and! evaluation.! A! model! was! then! developed! aligning! these! factors.! Further,! concrete! proposals! for! action! to! manage! these! factors! were! presented.! By! increasing! focus! on! these! key! factors! and! implement! proposed! measures! companies! will! increase! their! energy! performance! and! also! make! the! organization!aware!of!how!actions!affect!a!company’s!energy!performance.!

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Architecture, 2002.
Includes bibliographical references (p. 115-119).
Building energy simulation is an important tool for evaluating the energy consumption of a building and can provide guidance in the design of a building and its mechanical systems. EnergyPlus is a new energy simulation program meant to be a major advance over existing energy simulation programs. This study uses EnergyPlus to compare several alternative low-energy cooling systems for an office building in suburban London and compare them to the chilled ceiling system installed in the actual building. Prior to modeling the full -scale building, several validation studies demonstrate the accuracy of EnergyPlus and the author's competency as an EnergyPlus user. Systems considered include displacement ventilation, traditional mixing variable air volume ventilation, night cooling, and natural ventilation. Several changes were made to the EnergyPlus source code to model these systems appropriately. Most notable are a displacement ventilation three-node vertical temperature gradient model and a simple model for prediction of the natural ventilation rate. A detailed building model is created from inputs gathered from both building design documents and measured data. An excellent comparison between simulated and measured space temperatures over a one-month period demonstrates the accuracy of the model. System comparisons show that systems using free cooling from outside air and night cooling use the least energy and have the smallest equipment. Natural ventilation alone is insufficient to maintain summer comfort within the building, but could be used within a hybrid ventilation system. Conclusions are that EnergyPlus should be adopted for general use, because it represents a major improvement over previous energy simulation programs and is capable of modeling real-world buildings. A hybrid ventilation system would have the lowest building system energy use, but displacement ventilation is also a good choice, and could be implemented with few changes to the existing building.
by Erik L. Olsen.
S.M.

Reducing and managing the environmental impacts of building structures has become a priority of building stakeholders and within the architecture, engineering and construction (AEC) community; although, conflicting approaches and methods to combat the issues are present. For example, green building standards are widespread throughout the world; however each one has its own characteristics and consequently its own specific requirements. While all have proven to be effective rating systems and have similar requirements, the distinguishing characteristic that separates them is their treatment of performance and prescriptive metrics. The feature they all severely lack or currently limit is the inclusion of strict engineering evaluation through energy simulations; hence, the reason why they fail to offer procedural steps to meet performance metrics. How can design professionals design energy efficient buildings with such constraints? Fortunately, advances in technology have allowed design professionals access to content found in Building Information Modeling (BIM). However, extracting pertinent information for specific use in energy analysis is problematic because BIM software currently available is filled with interoperability issues when placed in external software for energy analysis and energy analysis software itself is created with many assumptions that affect the tabulated energy results. This research investigates current building rating systems, determines how current professionals meet energy requirements, and prove that it is possible to create an add-on feature to Autodesk Revit that will allow design professionals to extract the needed information to meet energy goals with actual prescribed methods of mechanical systems selection and evaluation.

This project has been carried out for the ALEC (Agence Locale de l'Energie et du Climat) of Grenoble urban area, a French energy and climate agency. It has been composed of several missions, all related to energy management in residential buildings. First, an annual energy use assessment have been conducted for two different building samples:  the eco-district of De Bonne in Grenoble and a sample of about 25 social housing buildings over the region. These two assessments showed that the average energy performance of newly built buildings is improving every year, notably under the stimulation of innovative projects such as De Bonne. Then, a more precise follow-up of construction and renovation social housing projects enabled to learn more about how to maintain energy facilities and to detect some common technical issues. The global conclusion of this project is that, although buildings are better designed today, energy performance remains fragile notably during construction and operation. To cope with that, some solutions exist and should be more systematically applied in future construction or renovation projects.

Energy benchmarking and disclosure policies exist in several local and state governments to manage the energy consumption of existing buildings and encourage energy efficient retrofits and upgrades, yet little is known about whether these efforts have improved overall energy efficiency. The purpose of this repeated-measures study was to examine the influence of New York City's (NYC's) Benchmarking Law (LL84) on the energy performance of the city's existing commercial buildings through investigating whether the energy performance of the city's existing commercial buildings significantly improved after the implementation of this policy. The study was based on Ostrom's institutional analysis and development framework. Paired-sample t tests were performed to statistically analyze the annually disclosed energy benchmarking data for 1,072 of NYC's existing commercial buildings that were benchmarked in both 2011 and 2016. Compared to 2011, the study results revealed statistically significant improvements in the energy performance of NYC's commercial buildings by 2016. On average, their site energy use intensity (EUI) significantly reduced by 5%, source EUI significantly decreased by 10%, greenhouse gas emissions significantly dropped by 12%, and ENERGY STAR performance rating significantly improved by 5%. However, these improvements were primarily achieved in 2012, 1 year after the city's energy benchmarking data were publicly disclosed. Additional measures should be considered to maintain continuous energy savings and greenhouse gas mitigation patterns. Positive social change implications include the potential to promote energy-efficient upgrades and inspire the adoption of sustainable building concepts.

Energy management has been an important function of organisations since the oil crisis of the mid 1970’s led to hugely increased costs of energy. Although the financial costs of energy are still important, the growing recognition of the environmental costs of fossil-fuel energy is becoming more important. Legislation is also a key driver. The UK has set an ambitious greenhouse gas (GHG) reduction target of 80% of 1990 levels by 2050 in response to a strong international commitment to reduce GHG emissions globally. This work is concerned with the management of energy consumption in buildings through the analysis of energy consumption data. Buildings are a key source of emissions with a wide range of energy-consuming equipment, such as photocopiers or refrigerators, boilers, air-conditioning plant and lighting, delivering services to the building occupants. Energy wastage can be identified through an understanding of consumption patterns and in particular, of changes in these patterns over time. Changes in consumption patterns may have any number of causes; a fault in heating controls; a boiler or lighting replacement scheme; or a change in working practice entirely unrelated to energy management. Standard data analysis techniques such as degree-day modelling and CUSUM provide a means to measure and monitor consumption patterns. These techniques were designed for use with monthly billing data. Modern energy metering systems automatically generate data at half-hourly or better resolution. Standard techniques are not designed to capture the detailed information contained in this comparatively high-resolution data. The introduction of automated metering also introduces the need for automated analysis. This work assumes that consumption patterns are generally consistent in the short-term but will inevitably change. A novel statistical method is developed which builds automated event detection into a novel consumption modelling algorithm. Understanding these changes to consumption patterns is critical to energy management. Leicester City Council has provided half-hourly data from over 300 buildings covering up to seven years of consumption (a total of nearly 50 million meter readings). Automatic event detection pinpoints and quantifies over 5,000 statistically significant events in the Leicester dataset. It is shown that the total impact of these events is a decrease in overall consumption. Viewing consumption patterns in this way allows for a new, event-oriented approach to energy management where large datasets are automatically and rapidly analysed to produce summary meta-data describing their salient features. These event-oriented meta-data can be used to navigate the raw data event by event and are highly complementary to strategic energy management.

PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO
COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
PROGRAMA DE EXCELENCIA ACADEMICA
As redes de sensores sem fio se constituem numa área que outorga grandes oportunidades para a oferta de uma série de aplicações inovadoras e com baixo custo. Os dispositivos destas redes são bastantes pequenos e sua fonte de alimentação são baterias. O tempo de vida destas é limitado, limitando assim o tempo da vida dos sensores e da rede como um todo. Por esta razão nos últimos anos o tema de eficiência energética tem atraído grande interesse de pesquisadores. O aumento do custo da energia e do consumo global da energia pelo setor de ICT (Information and Communications Technologies) têm crescido vertiginosamente devido ao aumento continuo do número de clientes e da demanda por aplicações de maior complexidade. Por tudo isso têm sido desenvolvidos distintos métodos e técnicas para economizar energia nas RSSF. Neste trabalho se implementam dois algoritmos que levam em conta critérios para economizar os custos de energia da rede e através de experimentos de simulação se avalia os mesmos. Nos resultados pode se observar as vantagens de trabalhar com sistemas que visam a eficiência energética.
The WSNs (Wireless Sensor Networks) belong to an area that gives rise to great opportunities to spread innovative and low cost applications. These kinds of networks are composed of tiny devices with limited energy. The main source of power supply for WSNs are batteries, which are limited in cycle life, thus limiting the sensors lifetime and the network as a whole. Due to that fact, the energy efficiency network is becoming the main concern to be addressed by researchers. Rising energy prices and global energy consumption by the ICT (Information and Communications Technologies) sector have grown dramatically due to the continuous increase in customer number and the demand for more complex applications. For the reasons outlined above, different energy-saving techniques for WSNs have been developed. Two energy-saving algorithms for WSNs were implemented in this thesis, and they were tested by experimental evaluation using simulation. The results obtained from the simulations showed the advantages of working with systems aiming at energy efficiency.

Windows, which are responsible for 45% of overall heat loss, play a major role in a building’s energy performance. Therefore, it is critical to measure window energy performance for existing buildings. This study aimed to evaluate the energy performance of windows to determine if replacement of windows is necessary. The evaluation was based on window location, height, orientation, and weather condition in a high-rise residential building. A thermal camera was used for measurements and statistical analyses were performed for measured data. Analysis results showed different performance of each side and floor of the building with a significant difference at the 0.05 level due to various temperatures, wind speeds, and directions. This study suggests using more efficient windows on upper floors, particularly from the fourth floor and above is beneficial as well as considering dominant wind speed and direction for the best configuration of window design.

This study aims at a preliminary characterization of system operation uncertainty. It bases this on an analysis of the energy consumption of 6 existing buildings on the Georgia Tech campus. The analysis is speculative in nature.

The cost of heating a house can be a large recurring cost for homeowners and rational buyers should capitalize this expense into the price they are willing to pay. I utilize hedonic price regressions to investigate if differences in heating costs are reflected in sales prices in the way theory would expect. I find that an increase in yearly heating expense is associated with a decrease in sales price ten times greater, this implies a capitalization rate of 30-50% under reasonable assumptions. These results are similar to or slightly lower than previous literature. Low capitalization of energy expense means that individuals are unlikely to invest in green home upgrades even when the net present value is positive.

The research activity carried out during the three years of the PhD course attended, at the Engineering Department of the University of Palermo, was aimed at the identification of an alternative predictive model able to solve the traditional building thermal balance in a simple but reliable way, speeding up any first phase of energy planning. Nowadays, worldwide directives aimed at reducing energy consumptions and environmental impacts have focused the attention of the scientific community on improving energy efficiency in the building sector. The reduction of energy consumption and CO2 emissions for heating and cooling needs of buildings is an important challenge for the European Union, because the buildings sector contributes up to 36% of the global CO2 emissions [1] and up to 40% of total primary energy consumptions [2]. Despite the ambitious goals set by the Energy Performance of Buildings Directive (EPBD) at the European level [1], which states that, by 2020, all new buildings and existing buildings undergoing major refurbishments will have to be Nearly Zero Energy Buildings (NZEB) [3,4], the critical challenge remains the improvement of the efficiency when upgrading the existing building stock to standards of the NZEB level [5]. The improvement of the energy efficiency of buildings and their operational energy usage should be estimated early in the design phase to guarantee a reduction in energy consumption, so buildings can be as sustainable as possible [6]. While a newly constructed NZEB can employ the “state of the art” of available efficient technologies and design practices, the optimization of existing buildings requires better efforts [7]. One way or the other, the identification of the best energy retrofit actions or the choice of a better technological solution to plan a building is not so simple. It has become one of the main objectives of several research studies, which require deep knowledge in the field of the building energy balance. The building thermal balance includes all sources and sinks of energy, as well as all energy that flows through its envelope. More in detail, the energy demand in buildings depends on the combination of several parameters, such as climate, envelope features, occupant behaviour and intended use. Indeed, the assessment of building energy performance requires substantial input data describing structures, environmental conditions [8], thermo-physical properties of the envelope, geometry, control strategies, and several other parameters. From the first design phases designers and researchers, which are trying to respect the prescriptions of the EPBD directive and to simultaneously ensure the thermal comfort of the occupants, must optimize all possible aspects that represent the key points in the building energy balance. As will be shown in Chapter A, the literature offers highly numerous complex and simplified resolution approaches [9]. Some are based on knowledge of the building thermal balance and on the resolution of physical equations; others are based on cumulated building data and on implementations of forecast models developed by machine-learning techniques [10]. Several numerical approaches are most widespread; these have undergone testing and implementing in specialised software tools such as DOE-2 [11], Energy Plus [12], TRNSYS [13] and ESP-r [14]. Such building modelling software can be employed in several ways on different scales; they can be simplified [15,16] or detailed comprehensively by different methods and numerical approaches [17]. Nevertheless, they are often characterised by a lack of a common language, which constitutes an obstacle for making a suitable choice. It is often more convenient to accelerate the building thermal needs evaluation and use the simplified methods and models. For example, a steady state approach for the evaluation of thermal loads is characterised by a good level of accuracy and low computational costs. However, its main limitation is that some phenomenon, such as the thermal inertia of the building envelope/structure, may be completely neglected. On the other hand, the choice of a more complex solution, such as the dynamic approach, uses very elaborate physical functions to evaluate the energy consumption of buildings. Although these dynamic simulation tools are effective and accurate, they have some practical difficulties such as collecting detailed building data and/or evaluating the proper boundary conditions. The use of these tools normally requires an expert user and a careful calibration of the model and do not provide a generalised response for a group of buildings with the same simulation, because they support a specific answer to a specific problem. Meanwhile the lack of precise input can lead to low-accuracy simulation. Anyway, in all cases it is necessary to be an expert user to implement, solve and evaluate the results, and these phases are not fast and not always immediately provide the correct evaluation, conducting the user to restart the entire procedure. In the field of energy planning, in order to identify energy efficiency actions aimed at a particular context, could be more convenient to speed up the preliminary assessment phase resorting to a simplified model that allows the evaluation of thermal energy demand with a good level of accuracy and without excessive computational cost or user expertise. The aim of this research, conducted during the three years of the PhD studies, is based on the idea of overcoming the limits previously indicated developing a reliable and a simple building energy tool or an evaluation model capable of helping an unskilled user at least in the first evaluation phase. To achieve this purpose, the first part of the research was characterised of an in-depth study of the sector bibliography with the analysis of the most widespread and used methods aimed at solving the thermal balance of buildings. After a brief distinction of the analysed methods in White, Black and Grey Box category, it was possible to highlight the strengths and weaknesses of each one [9]. Based on the analysis of this study, some alternative methods have been investigated. In detail, the idea was to investigate several Black-Box approaches; mainly used to deduce prediction models from a relevant database. This category does not require any information about physical phenomena but are based on a function deduced only by means of sample data connected to each other and which describes the behaviour of a specific system. Therefore, it is fundamental the presence of a suitable and well-set database that characterise the problem, so that the output data are strongly related to one or more input data. The completely absence of this information and the great difficulty in finding data, has led to the creation of a basic energy database which, under certain hypotheses, is representative of a specific building stock. For this reason, in the first step of this research was developed a generic building energy database that in a reliable way, and underlining the main features of the thermal balance, issues information about the energy performances. In detail, two energy building databases representative of a non-residential building-stock located in the European and Italian territory have been created. Starting from a well-known and calibrated Base-Case dynamic model, which simulates the actual behaviour of a non-residential building located in Palermo, it was created an Ideal Building representative of a new non-residential building designed with high energy performances in accordance whit the highest standard requirements of the European Community. Taking into consideration the differences existing in the regulations and technical standards about the building energy performance of various European countries, several detailed dynamic simulation models were developed. Moreover, to consider different climatic characteristics, different locations were evaluated for each country or thermal zone which represent the hottest, the coolest and the mildest climate. The shape factor of buildings, which represents the ratio between the total of the loss surfaces to the gross heated volume of a building, was varied from 0.24 to 0.90. To develop a representative database where the data that identify the building conditions are the inputs of the model linked to an output that describes the energy performances it was decided to develop a parametric simulation. In detail different transmittance values, boundary conditions, construction materials, and energy carriers were chosen and employed to model representative building stocks of European and Italian cities for different climatic zones, weather conditions, and shape factor; all details and the main features are described in Chapter B.   These two databases were used to investigated three alternative methods to solve the building thermal balance; these are: • Multi Linear Regression (MLR): identification of some simple correlations that uses well known parameters in every energy diagnosis [18–20]; • Buckingham Method (BM): definition of dimensionless numbers that synthetically describe the relationships between the main characteristic parameters of the thermal balance [21]; and • Artificial Neural Network (ANN): Application of a specific Artificial Intelligence (AI) to determine the thermal needs of a [22] building. These methods, belonging to the Black-Box category, permit solving a complex problem easier with respect to the White-Box methods because they do not require any information about physical phenomena and expert user skills. Only a small amount of data on well-known parameters that represent the thermal balance of a building is required. The first analysed alternative method was the MLR, described in Chapter C. This approach allowed to develop a simple model that guarantees a quick evaluation of building energy needs [19] and is often used as a predictive tool. It is reliable and, at the same time, easy to use even for a non-expert user since an in-depth knowledge in the use phase is not needed, and computational costs are low. Moreover, the presence of an accurate input analysis guarantees greater speed and simplicity in the data collection phase [23]. The basis for this model is the linear regression among the variables to forecast and two or more explanatory variables. The feasibility and reliability of MLR models is demonstrated by the publication of the main achieved results in international journals. At first, the MLR method was applied on a dataset that considered heating energy consumptions for three configurations of non-residential buildings located in seven European countries. In this way, it was developed a specific equation for each country and three equations that describe each climatic region identified by a cluster analysis; these results were published in [19]. In a second work [18], it was applied the same methodology to a set of data referring to buildings located in the Italian peninsula. In this case, three building analysed configurations, in accordance to Italian legislative requirements regarding the construction of high energy performance buildings, have been employed. The achievement of the generalised results along with a high level of reliability it was achieved by diversifying each individual model according to its climate zone. It was provided an equation for each climate zone along with a unique equation applicable to the entire peninsula, obviously with different degrees of reliability. An improved version of the latest work concerning the Italian case study appeared in the paper published in [20]. The revised model provided an ability to predict the energy needs for both heating and cooling. Furthermore, to simplify the data retrieval phase that is required for the use of the developed MLR tool, an input selection analysis based on the Pearson coefficient has been performed. In this way the explanatory variables, needful for an optimal identification of thermal loads, have been identified. Finally, a comprehensive statistical analysis of errors ensured high reliability. The second analysed alternative method represents an innovative approach in developing a flexible and efficient tool in the building energy forecast framework. This tool predicts the energy performance of a building based some dimensionless parameters implemented through the application of the Buckingham theorem. A detailed description of the methodology and results is discussed in the Chapter D and is also published in [21]. The Buckingham theorem represents a key theorem of the dimensional analysis since it is able to define the dimensionless parameters representing the building balance [24]. These parameters define the relationships between the descriptive variables and the fundamental dimensions. Such a dimensional analysis guarantees that the relationship between physical quantities remains valid, even if there is a variation of the magnitudes of the base units of measurement [25]. The dimensional analysis represents a good model to simplify a problem by means of the dimensional homogeneity and, therefore, the consequent reduction in the number of variables. Therefore, this model works well with different applications such as forecasting, planning, control, diagnostics and monitoring in different sectors. The application of the BM for predicting the energy performance of buildings determined nine ad hoc dimensionless numbers. The identification of a set of criteria and a critical analysis of the results allowed to immediately determine thought the dimensionless numbers and without using any software tool, the heating energy demand with a reliability of over 90%. Furthermore, the validation of the proposed methodology was carried out by comparing the heating energy demand that was calculated by a detailed and accurate dynamic simulation. The last Black-Box examined model was the application of Artificial Neural Networks. The ANNs are the most widely used data mining models, characterised by one of the highest levels of accuracy with respect to other methods but generally have higher computational costs in the developing phase [26]. The design of a neural network, inspired by the behaviour of the human brain, involves the large number of suitably connected nodes (neurons) that, upon applications of simple mathematical operations, influence the learning ability of the network itself [27]. Also in this case, as described in Chapter E, this methodology was applied at the two different energy databases. In [22], the ANN was used to predict the demand for thermal energy linked to the winter climatization of non-residential buildings located in European context, while in another work under review, the ANN was used to determine the heating and cooling energy demand of a representative Italian building stock. The validation of the ANNs was carried out by using a set of data corresponding to 15% of the initial set which were not used to train the ANNs. The obtained good results (determination coefficient values higher than 0.95 and Mean Absolute Percentage Error lower than 10%) show the suitability of the calculation model based on the use of adaptive systems for the evaluation of energy performance of buildings. Simultaneously, a deep analysis of the investigated problem, underlines how to determine the thermal behaviour of a building trough Black-Box models, particular attention must be paid to the choice of an accurate climate database that along with thermophysical characteristics, strongly influence the thermal behaviour of a building [9]. In detail, to develop a predictive model of thermal needs, it is also necessary to pay close attention to the climate aspects. In the literature, many studies use the degree day (DD) to predict building energy demand, but this assessment, through the use of a climatic index, is correct only if its determination is a function of the same weather data used for the model implementation. Otherwise, the predictive model is generally affected by a greater evaluation error; all these aspects are deeply discussed analysing a specific Italian case study in Chapter F, and the main results are published in [8]. The results achieved during the three years of PhD research, make it possible to affirm that each model can be used to solve thermal building balance by knowing merely a few parameters representative of the analysed problem. Nonetheless, some questions may be asked: Which of these models can be identified as the most efficient solution? Is it possible to compare the performances of these models? Is it possible to choose the most efficient model based on some specific phase in the evaluation? To attempt to answer these questions, during the research period it was decided to compare the three selected alternative models by applying a Multi Criteria Analysis (MCA), that explicitly evaluates multiple criteria in decision-making. It is a useful decision support tool to apply to many complex decisions by choosing among several alternatives. The idea rising thanks to the scientific collaboration with the VGTU University of Vilnius, Lithuanian, in the person of Prof. A. Kaklauskas and Prof. L. Tupènaitè, experts in the field of multi-criteria analysis. At the first time a multi-criteria procedure was applied to determine the most efficient alternative model among some resolution procedures of a building’s energy balance. This application required extra effort in defining the criteria and identifying a team of experts. To apply the MCA, it was necessary to identify the salient phases of the evaluation procedure to explain the most sensitive criteria for acquiring conscious, truthful answers that only a pool of experts in the field can provide. Details of this work were carried out during the period of one-month research in Vilnius, from April to May 2019, where it was possible to improve the application of the Multiple Criteria Complex Proportional Evaluation (COPRAS) method for identifying the most efficient predictive tool to evaluate building thermal needs. These results are collected in Chapter G and the main results are explained in a paper under review in the Journal “Energy” from September. The identification of the most efficient alternative model to solve the building energy balance through the application of a specific MCA, allowed to deepen the identified methodology and improve research. In particular, the most efficient alternative resolution model was the subject of the research that took place during the research period at the RWTH in Aachen University, Germany with Prof. M. Traverso, Head of the INaB Department, from September 2018 to March 2019. The experience in the field of LCA and the possibility of identifying the environmental impacts linked to the building system, has led the research to investigate neural networks for a dual and simultaneous environmental-energy analysis. The results confirm that the application of ANNs is a good alternative model for solving the energy and environmental balance of a building and for ensuring the development of reliable decision support tools that can be used by non-expert users. ANNs can be improved by upgrading the training database and choosing the network structure and learning algorithm. The results of this research are collected in Chapter H and published in [28].

The renewal of the existing housing stock is a slow progress and theexisting is quite old. The existing housing stock represents a largeamount of the bought energy need for heating and a simple method forquickly determining the energy performance is needed.There are many different methods for estimating the energyperformance of buildings. In this report the feasibility of using asingle-variate steady state method to investigate energy performancehas been tested. Bought energy need in single-family houses in a coldclimate has been observed during the cold period. The observationshave been made with the help of a measurement system requiring aminimal installation. The heat loss factor of the observed buildingshas been determined using the energy signature approach and differenttime scales have been tried.The result shows that to determine the heat loss factor of single-familybuildings, a single-variate method is valid. Daily averages are a goodtime scale for houses using radiators under the windows to heat thebuilding. Buildings with floor heating in concrete slab need to have alonger time scale, around 3 days.The method does not account for occupancy levels and separateenergy use in specific installations is not easy to estimate with theminimalized measurement setup. A combination of heat sources suchas district heating, electrical heating, heat recovery and/or fire stove isproblematic to handle with the energy signature method if enoughobservations for al heat sources can be achieved.
Godkänd; 2014; 20140916 (ysko); Nedanstående person kommer att hålla licentiatseminarium för avläggande av teknologie licentiatexamen. Namn: Gustav Nordström Ämne: Träbyggnad/Timber Structures Uppsats: Use of energy-signature method to estimate energy performance in single-family buildings Examinator: Biträdande professor Helena Lidelöw, Institutionen för Samhällsbyggnad och naturresurser, Luleå tekniska universitet Diskutant: Teknologie doktor Jutta Schade, avd. för Byggproduktion, Institutionen för Samhällsbyggnad och naturresurser, Luleå tekniska universitet Tid: Fredag den 31 oktober 2014 kl 10.00 Plats: F1031, Luleå tekniska universitet

Energy efficiency of buildings is attracting significant attention from the research community as the world is moving towards sustainable buildings design. Energy efficient approaches are measures or ways to improve the energy performance and energy efficiency of buildings. This study surveyed various energy-efficient approaches for commercial building and identifies Envelope Thermal Transfer Value (ETTV) and Green applications (Living wall, Green facade and Green roof) as most important and effective methods. An in-depth investigation was carried out on these energy-efficient approaches. It has been found that no ETTV model has been developed for sub-tropical climate of Australia. Moreover, existing ETTV equations developed for other countries do not take roof heat gain into consideration. Furthermore, the relationship of ETTV and different Green applications have not been investigated extensively in any literature, and the energy performance of commercial buildings in the presence of Living wall, Green facade and Green roof has not been investigated in the sub-tropical climate of Australia. The study has been conducted in two phases. First, the study develops the new formulation, coefficient and bench mark value of ETTV in the presence of external shading devices. In the new formulation, roof heat gain has been included in the integrated heat gain model made of ETTV. In the 2nd stage, the study presents the relationship of thermal and energy performance of (a) Living wall and ETTV (b) Green facade and ETTV (c) Combination of Living wall, Green facade and ETTV (d) Combination of Living wall, Green Roof and ETTV in new formulations. Finally, the study demonstrates the amount of energy that can be saved annually from different combinations of Green applications, i.e., Living wall, Green facade; combination of Living wall and Green facade; combination of Living wall and Green roof. The estimations are supported by experimental values obtained from extensive experiments of Living walls and Green roofs.

Computer and Information Science
Ph.D.
The continuous growth in computing capability has expedited the scientific discovery and enabled scientific applications to simulate physical phenomena for increased problem sizes. However, as the computing capability escalates, power constraints are becoming a first-order concern for high performance computing (HPC) facilities. For example, the U.S. Department of Energy has set a power constraint of 20 MW to each exascale machine. How to achieve the target performance under power constraints remains to be an issue. Therefore, efficient operation of these facilities requires power constraints to be taken into account at all layers, which potentially impacts the performance and energy efficiency. In order to improve the performance and energy efficiency for computing and storage resources under power constraints, I proposed the following three techniques. First, I developed a power-aware checkpointing model through exploring the interplay among power capping, temperature, reliability, performance, and energy efficiency. Applying the model leads to maximized performance and energy efficiency, and minimized data movements over storage systems. Second, I characterized the performance and energy efficiency of HPC workflows on heterogeneous processors. In addition, I also characterized how scientific simulation and analysis react to power capping differently and how they vary based on error resilience. Based on the characterization of HPC workflows, I developed a reliability-aware platform configuration model to determine the optimal platform configuration which includes power allocation and distribution, power capping levels, and computing scales for power-constrained HPC workflows. Third, I developed a proactive burst buffer draining scheme to minimize the I/O provisioning requirement of permanent storage systems while preserving the system I/O performance. Facing power constraints, reducing the storage provisioning level directly decreases the power consumption of storage systems. Applying the proactive burst buffer draining scheme minimizes the storage provisioning level and power consumption without compromising the storage I/O performance.
Temple University--Theses

Energy efficiency is an important challenge in the field of High Performance Computing (HPC). High energy requirements not only limit the potential to realize next-generation machines but are also an increasing part of the total cost of ownership of an HPC system. While at large HPC systems are becoming increasingly energy proportional in an effort to reduce energy costs, interconnect links stand out for their inefficiency. Commodity interconnect links remain ¿always-on¿, consuming full power even when no data is being transmitted. Although various techniques have been proposed towards energy- proportional interconnects, they are often too conservative or are not focused toward HPC. Aggressive techniques for interconnect energy savings are often not applied to HPC, in particular, because they may incur excessive performance overheads. Any energy-saving technique will only be adopted in HPC if there is no significant impact on performance, which is still the primary design objective. This thesis explores interconnect energy proportionality from a performance perspective. In this thesis, first a characterization of HPC applications is presented, making a case for the enormous potential for interconnect energy proportionality with HPC applications. Next, an HPC interconnect with on/off based links, modeled after the IEEE Energy Efficient Ethernet protocol, is evaluated. This evaluation while presenting a relationship between performance impact and energy over HPC applications also emphasizes the need for performance focused designs in energy efficient interconnects. Next, an adaptive mechanism, PerfBound, is presented that saves link energy subject to a bound on application performance overheads. Finally this evaluation structure is applied into an intermediate link power state, in addition to the traditional on and off states. Results of this study, over 15 production HPC applications show that, compared to current day always-on HPC interconnects, link energy can be reduced by unto 70%, while application performance overhead is bounded to only 1%.
La eficiencia energética es un gran reto en el área de la Supercomputación (HPC), las grandes necesidades de energía no solo limitan el potencial de las computadoras de nueva generación, sino que también aumentan el coste de funcionamiento de estos sistemas. Mientras que los sistemas HPC tienden a ser cada vez más energéticamente proporcionales en un empeño por reducir costes, los enlaces de interconexión siguen siendo muy ineficientes. Los enlaces de interconexión comunes funcionan en modo "always-on", es decir, consumiendo energía incluso cuando no transmiten. Aunque se han propuesto algunas técnicas que ayuden a la proporcionalidad energética de los enlaces de interconexión, éstas han sido muy agresivas o poco enfocadas hacia su uso con sistemas HPC. Las técnicas de ahorro energético para los enlaces más agresivas no suelen ser utilizadas en HPC, particularmente porque degradan excesivamente el rendimiento. Cualquier técnica de ahorro energético solo será adoptada en sistemas HPC si no hay un impacto excesivo en el rendimiento, el cual es el principal objetivo de estos sistemas. En esta tesis, primeramente se presenta una nueva caracterización de aplicaciones HPC, remarcando el enorme potencial de la proporcionalidad en los enlaces de interconexión proporcionales para aplicaciones HPC. Seguidamente, se evaluará siguiendo el protocolo "IEEE Energy Efficient Ethernet" un link de interconexión on/off. Esta evaluación presentará una relación de impacto energético y rendimiento en aplicaciones HPC, enfatizando en la necesidad de usar un enlace de interconexión enfocados a la eficiencia. Se continuará con la presentación de un mecanismo adaptivo, PerfBound, que ahorra energía respetando unos límites máximos de impacto en el rendimiento. Finalmente, esta estructura es aplicada a un nuevo estado intermedio de funcionamiento adicional a los estados tradicionales on/off. Los resultados de este estudio, muestran que en más de 15 aplicaciones HPC la energía en los enlaces puede ser reducida en un 70% en comparación con enlaces "always-on", mientras que el impacto en el rendimiento es de tan solo un 1%.

The scaling of MOS transistors into the nanometer regime opens the possibility for creating large Network-on-Chip (NoC) architectures containing hundreds of integrated processing elements with on-chip communication. NoC architectures, with structured on-chip networks are emerging as a scalable and modular solution to global communications within large systems-on-chip. NoCs mitigate the emerging wire-delay problem and addresses the need for substantial interconnect bandwidth by replacing today’s shared buses with packet-switched router networks. With on-chip communication consuming a significant portion of the chip power and area budgets, there is a compelling need for compact, low power routers. While applications dictate the choice of the compute core, the advent of multimedia applications, such as three-dimensional (3D) graphics and signal processing, places stronger demands for self-contained, low-latency floating-point processors with increased throughput. This work demonstrates that a computational fabric built using optimized building blocks can provide high levels of performance in an energy efficient manner. The thesis details an integrated 80- Tile NoC architecture implemented in a 65-nm process technology. The prototype is designed to deliver over 1.0TFLOPS of performance while dissipating less than 100W. This thesis first presents a six-port four-lane 57 GB/s non-blocking router core based on wormhole switching. The router features double-pumped crossbar channels and destinationaware channel drivers that dynamically configure based on the current packet destination. This enables 45% reduction in crossbar channel area, 23% overall router area, up to 3.8X reduction in peak channel power, and 7.2% improvement in average channel power. In a 150-nm sixmetal CMOS process, the 12.2 mm2 router contains 1.9-million transistors and operates at 1 GHz at 1.2 V supply. We next describe a new pipelined single-precision floating-point multiply accumulator core (FPMAC) featuring a single-cycle accumulation loop using base 32 and internal carry-save arithmetic, with delayed addition techniques. A combination of algorithmic, logic and circuit techniques enable multiply-accumulate operations at speeds exceeding 3GHz, with singlecycle throughput. This approach reduces the latency of dependent FPMAC instructions and enables a sustained multiply-add result (2FLOPS) every cycle. The optimizations allow removal of the costly normalization step from the critical accumulation loop and conditionally powered down using dynamic sleep transistors on long accumulate operations, saving active and leakage power. In a 90-nm seven-metal dual-VT CMOS process, the 2 mm2 custom design contains 230-K transistors. Silicon achieves 6.2-GFLOPS of performance while dissipating 1.2 W at 3.1 GHz, 1.3 V supply. We finally present the industry's first single-chip programmable teraFLOPS processor. The NoC architecture contains 80 tiles arranged as an 8×10 2D array of floating-point cores and packet-switched routers, both designed to operate at 4 GHz. Each tile has two pipelined singleprecision FPMAC units which feature a single-cycle accumulation loop for high throughput. The five-port router combines 100 GB/s of raw bandwidth with low fall-through latency under 1ns. The on-chip 2D mesh network provides a bisection bandwidth of 2 Tera-bits/s. The 15-FO4 design employs mesochronous clocking, fine-grained clock gating, dynamic sleep transistors, and body-bias techniques. In a 65-nm eight-metal CMOS process, the 275 mm2 custom design contains 100-M transistors. The fully functional first silicon achieves over 1.0TFLOPS of performance on a range of benchmarks while dissipating 97 W at 4.27 GHz and 1.07-V supply. It is clear that realization of successful NoC designs require well balanced decisions at all levels: architecture, logic, circuit and physical design. Our results demonstrate that the NoC architecture successfully delivers on its promise of greater integration, high performance, good scalability and high energy efficiency.

Software developers are faced with several challenges when creating applications for the new generation of mobile devices. Smartphones and tablets have limited processing power and memory resources, and a small battery is the only thing that keeps the hardware components running. End users have little patience for slow applications that drain the batteries of their devices. To satisfy the needs of their customers, developers must take these hardware limitations into account; they must make an effort to optimize the performance and energy efficiency of their applications. This thesis provides a general overview of performance and energy optimization in the mobile domain. A specific sub-area is explored in great detail: the use of native C code for performance and energy optimization of Android applications. An experiment was conducted to see how the performance of native code compares to that of Java. This is the first time that such measurements have been made on both emulators and physical devices. The devices were running recent versions of Android that have not been used for similar experiments before: 2.3.3, 3.2 and 4.0.3. It is also the first time that native code has been compared to Java in terms of energy consumption. The results show that the latest updates to the Android platform have brought Java closer to native code in terms of performance, but native code is still the best choice for certain types of operations. It is also evident that there is a close correlation between performance and energy efficiency. Finally, the results show that Android emulators are unreliable for performance measurements. This could be a reason to question the validity of previous research.