In the last decade, efficient use of energy has become a topic of global significance, touching almost every area of modern life, including computing. From mobile to desktop to server, energy efficiency concerns are now ubiquitous. However, approaches to the energy problem are often piecemeal and focus on only one area for improvement. I argue that the strands of the energy problem are inextricably entangled and cannot be solved in isolation. I offer a high-level view of the problem and, building from it, explore a selection of subproblems within the field. I approach these with various levels of formality, and demonstrate techniques to make improvements on all levels.

Water and energy are very necessary resources for operating any chemical plant and contribute to total costs. Economic reasons notwithstanding, the processing industry has been incentivised to practise sustainable production in which the consumption of energy and water are more efficient, in response to stringent environmental legislation and public perception. Published literature exists for the independent investigation of water and energy optimisation in batch plants. It has been established for the individual problems that, a true optimum can only be obtained if batch production scheduling and water use or energy optimisation are performed simultaneously. However, the simultaneous optimisation of both water and energy within the same production scheduling framework has been largely ignored, due to the potential complexities of such a problem. Additionally, literature addressing the minimisation of water in fixed load problems has usually assumed that the water using operations (washing) are sequence independent. This is unlikely, as equipment units usually perform more than one task in multipurpose batch plants. Since the sequence of tasks in a unit influences both the occurrence and extent of washing in the unit, appropriate consideration of task sequences during production can contribute to wastewater minimisation. This thesis presents a mathematical formulation for the production scheduling of multipurpose batch plants, in which sequence dependent changeover costs are addressed. When compared to an existing formulation, the proposed formulation leads to a smaller sized model with fewer binary variables, continuous variables and constraints for a given case study, although the same objective was obtained. Expanding upon this, a mathematical formulation for simultaneous batch production scheduling and wastewater minimisation, for which the water requirement in a unit is dependent on tasks and their successors, is presented. The effectiveness of the formulation was demonstrated using two case studies. The results show improvements in profit and reduced wastewater generation when the sequence of tasks is taken into consideration. One case study saw water savings of 48% achieved with this method. The formulation was extended to incorporate process integration in the form of direct water reuse, which resulted in a further improvement in profit and water use. The third contribution in this thesis is a simultaneous method for the optimisation of energy and water embedded within a scheduling framework. In addition, opportunities for direct and indirect heat integration as well as direct and indirect water reuse were explored with the objective of improving the profitability of the plant while minimising water and external utility usage. The applicability of the method was demonstrated with three case studies. The developed formulation proved superior to a method that solved the same problem sequentially. / Thesis (PhD)--University of Pretoria, 2017. / Chemical Engineering / PhD / Unrestricted

Major energy-consuming countries implemented new laws on energy-efficiency during the course of 2013. The new energy-efficiency law make provision for a 16% reduction in energy intensity by 2015 in China. New law in the United States of America requires new fuel-economy standards. European Union law aims for a cut of 20% in energy demand for the countries forming part of the European Union. Japan, with the country's new energy strategy aims to decrease electricity demand with 10% by 2030 as stipulated in the new energy strategy. South Arica is currently experiencing a shortage in electricity generating capacity and operates within its reserve margin. The construction of new power stations is in process to address the shortage but Eskom must finance these assets by increasing the electricity tariff. Electricity prices are predicted to double from 2013 to 2017. In addition to the tariff increases, the Energy Conservation Scheme (ECS) is also planned by Eskom whereby all electricity consumers have to reduce their electricity consumption by 10% or face penalties. Energy efficiency initiatives in South Africa will help meet some of the country's social, economic, and environmental goals. These initiatives are important as they immediately tackle the problem of electricity shortages and are a cost-effective way of increasing available electricity supply. The aim of this study was to determine the need for businesses in the Vaal Triangle to be resource efficient and practice clean production in order to be able to capitalise on that need. With the current knowledge and technology available, Resource Efficiency and Cleaner Production (RECP) will prove to be a future necessity for industry. To determine the perceived readiness towards a green economy contribution is thus of importance. The study did a review on RECP, energy efficiency, supply of energy in South Africa, focus areas for energy efficiency and the benefits thereof. The study discussed energy efficiency incentive schemes and subsidisation funds available in South Africa. The study assessed the primary fields for RECP, the drivers and barriers to RECP and the willingness to participate in RECP initiatives in the Vaal Triangle. The study concluded that there exists a need in the Vaal Triangle for RECP initiatives and that there exists potential for the start of a green economy in the region. The research indicated the reaction towards RECP initiatives to be very positive in the studied region. / MBA, North-West University, Potchefstroom Campus, 2015

Major energy-consuming countries implemented new laws on energy-efficiency during the course of 2013. The new energy-efficiency law make provision for a 16% reduction in energy intensity by 2015 in China. New law in the United States of America requires new fuel-economy standards. European Union law aims for a cut of 20% in energy demand for the countries forming part of the European Union. Japan, with the country's new energy strategy aims to decrease electricity demand with 10% by 2030 as stipulated in the new energy strategy. South Arica is currently experiencing a shortage in electricity generating capacity and operates within its reserve margin. The construction of new power stations is in process to address the shortage but Eskom must finance these assets by increasing the electricity tariff. Electricity prices are predicted to double from 2013 to 2017. In addition to the tariff increases, the Energy Conservation Scheme (ECS) is also planned by Eskom whereby all electricity consumers have to reduce their electricity consumption by 10% or face penalties. Energy efficiency initiatives in South Africa will help meet some of the country's social, economic, and environmental goals. These initiatives are important as they immediately tackle the problem of electricity shortages and are a cost-effective way of increasing available electricity supply. The aim of this study was to determine the need for businesses in the Vaal Triangle to be resource efficient and practice clean production in order to be able to capitalise on that need. With the current knowledge and technology available, Resource Efficiency and Cleaner Production (RECP) will prove to be a future necessity for industry. To determine the perceived readiness towards a green economy contribution is thus of importance. The study did a review on RECP, energy efficiency, supply of energy in South Africa, focus areas for energy efficiency and the benefits thereof. The study discussed energy efficiency incentive schemes and subsidisation funds available in South Africa. The study assessed the primary fields for RECP, the drivers and barriers to RECP and the willingness to participate in RECP initiatives in the Vaal Triangle. The study concluded that there exists a need in the Vaal Triangle for RECP initiatives and that there exists potential for the start of a green economy in the region. The research indicated the reaction towards RECP initiatives to be very positive in the studied region. / MBA, North-West University, Potchefstroom Campus, 2015

Energy prices are on the rise, and with it the interest in saving energy. In the housing sector this means that methods for energy optimising buildings, retrofitting, are increasingly important. There are many studies concerning the retrofitting of buildings built before 2000, but less concerning buildings of more recent date. In cooperation with the housing company Uppsalahem, this report explores minor retrofitting solutions for the apartment buildings in Ekebyvallen/Uppsala which were built 2007. The aim was foremost to find solutions for Ekebyvallen but also to assess the possibilities of applying them to a wider range of buildings. A simulation of the energy balance in one of the buildings in Ekebyvallen was performed with the software VIP energy. The simulation together with a field study show weak spots of the energy usage in the buildings and based on these four retrofitting solutions were proposed. The methods; 1) reducing the airflow in the ventilation units, 2) adjusting the heating in common areas, 3) reducing air leakage out of buildings and 4) adjusting the settings of lighting sensors and timers. All are effectively free from investments and also applicable on buildings with similar issues. Thus, these are effective methods of saving energy and consequently, saving money in recently built buildings. The methods are tailored for Ekebyvallen but are with benefit considered for apartment buildings of both recent date and those built before 2000.

The optimal design and operation of an energy supply system is very important for the matching of the energy production and consumption especially in the residential-tertiary sector characterized by an energy demand with a high variability. The main objective of this thesis is to develop an optimisation environment for the preliminary design and analysis of polygeneration plants. The optimisation models are organized in different units represented by blocks that can be connected between each other to create the flowsheet of the polygeneration system. To characterize the energy demand in the residential and tertiary sector a graphic methodology has been developed to select typical energy demand days from a yearly energy demand profile. The environment developed has been applied to two case studies: a small scale polygeneration plant using a liquid desiccant system for air conditioning and a polygeneration plant connected to a district heating and cooling network.

The environmental impact from our energy production and use today is a central concern for every major decision maker regardless of interest area. Together with transport and industry, housing and services is a major contributor to our energy consumption. In 2013 housing and services accounted for 38% of the energy consumption in Sweden Therefore, energy consumption in buildings has become an area of great importance with many technological solutions developing to meet the demands from investors and legislation. However, present solutions primarily aim to solve current problems, while ongoing technological and social development is setting new conditions for future buildings. This study investigates the future of office buildings heading towards a more flexible work environment. Advancement of technology accompanied with new emerging economic and social practices is facilitating the flexibility, as well as remote work and more out-of-office time, with possible decrease of the thermal energy produced by humans and equipment. In addition, desktop computers will be replaced by energy efficient thin clients, tablets, and phones while other equipment is also becoming more energy efficient, resulting in reduced secondary heat production and thus lower internal gains. This scenario supposes reduced internal gains, resulting in decreased cooling requirements but also increased heating requirements. However, an alternative scenario with increased internal gains is also likely, due to activity-based workplaces. Activity-based offices dispose of personal desks, instead utilising activity-based areas where employees choose an area or desk where to work, depending on their current task. Disposing of personal desks supports higher occupancy, as employees working elsewhere don’t occupy workplaces at the office. Thus, the amount of desks can be matched to the actual amount of employees working at the office during peak loads. These scenarios are developed, quantified, and used as a basis for the building simulation models. These models are then optimised to meet these new conditions, utilising simulation and multi objective optimisation. The key finding is that office buildings are resilient to changing conditions, and that a state-of-theart office from today meet the demands of tomorrow. / Miljöpåverkan från vår produktion och energianvändning är idag är en central fråga för varje större beslutsfattare oavsett intresse i området. Tillsammans med transport och industri, är bostäder och service en viktig bidragande orsak till vår energiförbrukning. År 2013 bostäder och service stod för 38% av energiförbrukningen i Sverige. Därför har energiförbrukningen i byggnader kommit att få stor betydelse, vilket driver utvecklingen mot nya tekniska lösningar för att möta kraven från investerare och lagstiftning. De nuvarande lösningarna syftar dock främst till att lösa nuvarande problem, samtidigt som teknisk och social utveckling skapar nya förutsättningar för framtida byggnader. Detta projekt undersöker framtiden för kontorsbyggnader, där utvecklingen verkar vara på väg mot distansarbete, outsourcing, och mer arbetstid spenderad utanför kontoret, vilket minskar mängden interna laster som värmer upp kontoret. Samtidigt utvecklas stationära datorer och annan utrustning som ersättas med energieffektiva tunna klienter, tablets, och smarta telefoner, vilket minskar de interna lasterna ytterligare. Ett alternativt scenario är aktivitetsbaserade kontor, där de anställda inte har sin egen arbetsyta, utan istället använder aktivitetsbaserade områden beroende på arbetsuppgift. Detta scenario kan tänkas leda till ökade interna laster då ytan kan användas mer effektivt, som kan kompensera för användning av mer energieffektiv kontorsutrustning. Projektet undersöker tänkbara framtida scenarier och hur framtida kontor kan anpassas för att möta dessa nya förutsättningar med hjälp av klimat- och energisimuleringsmjukvara. Resultaten tyder på flera tydliga trender i användningen av kontorsbyggnader, men effekterna av dessa trender kan resultera i flera scenarier. Därför projektet omfattar flera scenarier för att utvärdera spannet av möjligheter. Simuleringarna tyder på att kontorsbyggnader är motståndskraftiga mot förändrade villkor, och att ett modernt kontor från idag kan möta morgondagens behov.

La optimización de los sistemas de bombeo se suele realizar a través de las curvas características de la red (asociadas con las curvas resistentes). Estas curvas están sujetas a la resistencia generada por el usuario en función de las necesidades de caudal y presión en cada punto de consumo. Dicha resistencia es muy variable y difícil de determinar lo que hace que el cálculo de las curvas sea poco práctico. El problema radica en que al no definirse adecuadamente las curvas resistentes, no se conocen las necesidades reales de caudal y presión de la red. Por lo tanto no se puede estimar el exceso de energía aportado por las bombas ni el aumento de costos de operación que esto representa. Sin embargo, existe otro tipo de curva denominada curva de consigna (CC). Dicha curva ha sido poco estudiada hasta ahora y su cálculo es relativamente fácil. De ahí que el presente trabajo tiene como objetivo la optimización de la energía y de los costes de bombeo mediante el uso de la CC. Para cumplir con el objetivo, primero se estudia el cálculo de la CC en redes de agua con múltiples estaciones de bombeo, consumos no dependientes y dependientes de la presión, y sin tanques de almacenamiento. Posteriormente, se lleva a cabo la optimización sólo desde la perspectiva energética (caudal y altura de bombeo). Para ello se realiza la búsqueda de la distribución de caudales óptima entre las estaciones de bombeo que conlleve a las CC óptimas. Se proponen dos métodos: uno discreto (M-D) y otro continuo (M-C). El M-D considera la distribución de caudales como una variable discreta. La distribución óptima se obtiene de un conjunto de soluciones previamente definidas. En el M-C la distribución de caudales se asume como variable continua. La solución óptima viene dada por el uso de un algoritmo de optimización. Se han usado los algoritmos: Hooke-Jeeves y Nelder-Mead. El siguiente paso es la optimización de costos de operación (costos de bombeo y costos de producción de agua). Para ello se parte del M-C y se incluyen además las tarifas de energía, las tarifas de producción de agua y un criterio sobre el rendimiento mínimo esperado en las estaciones de bombeo. El último paso consiste en la optimización energética y de costos en redes con tanques. La inclusión de tanques implica la modificación del cálculo de la CC y por ende la metodología de optimización. En la función de costes se incluyen además de los costes de bombeo y de producción, costes de penalización por incumplimiento de presiones y de volúmenes de reserva. Al incluirse los tanques, incrementa el número de variables de decisión. Por lo que, es necesario el uso de algoritmos más potentes. Se han usado el Differential Evolution y el Hybrid Algorithm. Este último es un aporte añadido de este trabajo. La metodología de optimización se aplica a cinco redes de distribución: TF, Catinen, Coplaca, Anytown y Richmond. Los tanques sólo se consideran en las dos últimas redes. En el caso de la red TF se realiza una demostración sin entrar en profundidad de la selección de bombas a través del uso de las CC óptimas. Sin embargo, este paso está fuera de los límites de este trabajo. Tampoco se consideran condiciones de operación múltiples de la red, ni la fiabilidad en el caso de la remoción de tanques o sistemas de bombeo. No obstante, los resultados obtenidos evidencian que los sistemas de bombeo operados usando la CC pueden mejorar sus costos operativos hasta en un 12%. La metodología proporciona información sobre las estaciones de bombeo que representan mayores ahorros frente a aquellas que son menos importantes o innecesarias. Además, el método ha permitido demostrar que mejores condiciones de bombeo (bajas tarifas de energía y altos rendimientos) no siempre significan menores costos de operación. Finalmente, algunos resultados muestran la posible utilidad del método para optimizar tanto el uso como la ubicación de los tanqu / Usually, pumping optimisation in water distribution networks is carried out by means of the system head curves (SHCs), also known as the resistance curves (RCs). These curves are subjected to the resistance generated by the users, according with the flow and pressure head needs at the final points of demand. Such resistance is highly variable and hard to determine. Thus the calculation of the RCs and all the points that define them results impractical. As a RCs suitable calculation is not possible, real flow and pressure needs of the network are not known. Therefore, neither energy excess of the pumping regarding the real requirements nor the raising operating costs due to such excess, are estimated. However, there is another type of SHC defined as the setpoint curve (SC). It can be easily calculated, but has been poorly studied so far. Thus, this work aims the optimisation of the energy use and operating costs in pumping systems by using the SCs. To achieve the objective, first of all the SC calculation is studied for networks with several pumping stations, non-pressure driven demands, pressure-driven demands, and without tanks. Next, the optimisation is performed only from the energy point of view (i.e. flow and pumping head required). For that, a search of the optimum flow distribution among pumping stations to find the optimum SCs is performed. Two methods are proposed: the discrete (D-M) and the continuous (C-M). The D-M considers the flow distribution as a discrete variable. The optimum flow distribution is obtained from a set of solutions defined previously. In the C-M, the flow distribution is assumed as a continuous variable. The optimum solution comes from using optimisation algorithms. Two algorithms have been applied: Hooke-Jeeves and Nelder-Mead. Then, the cost optimisation (pumping cost and water production cost) is developed. For that purpose, the M-C is used as starting point. Then, energy tariffs, water production fares and the minimum expected efficiency at the pumping stations, are included. The last step consists in the energy and cost optimisation in networks with tanks. When tanks are included the SC calculation methodology changes. Hence, the optimisation process also does. In that sense, besides the costs of pumping and water production, the cost function also considers penalty costs for unaccomplished minimum pressures and minimum storage leves. Moreover, tanks inclusion also rises the number of decision variables. Thus, the use of more powerful algorithms is required. In that context, the Differential Evolution and the Hybrid Algorithm have been applied. The last one is an additional contribution of this work. The optimisation methodology is applied to five distribution networks: TF, Catinen, Coplaca, Anytown and Richmond. Tanks are only considered in the last two networks. In the case of TF network, demonstrative pumps selection (without going into great depth) by the optimum SCs application is done. However pumps sizing and selection study is out of the scope of this research. Neither multiple operation conditions nor reliability (i.e. in the case that tanks or pumping stations are removed), are considered. Nevertheless, the results obtained evidence that pumping systems operated by mean of the optimum SCs could reduce their operating costs up 12%. The methodology also gives information about which pumping stations represent major savings and which are less important or not needed. Besides, the method demonstrates that better pumping conditions (i.e. low energy tariffs and high efficiencies) not always mean lower operating costs. Finally, some results show that the method could be useful for the optimisation of both placement and use of storage tanks. / L'optimització dels sistemes de bombament se sol realitzar a través de les corbes característiques de la xarxa (associades amb les corbes resistents). Aquestes corbes estan subjectes a la resistència generada per l'usuari en funció de les necessitats de cabal i pressió en cada punt de consum. Aquesta resistència és molt variable i difícil de determinar el que fa que el càlcul de les corbes siga poc pràctic. El problema radica que al no definir-se adequadament les corbes resistents, no es coneixen les necessitats reals de cabal i pressió de la xarxa. Per tant no es pot estimar l'excés d'energia aportat per les bombes ni l'augment de costos d'operació que açò representa. No obstant açò, existeix un altre tipus de corba denominada corba de consigna (CC). Aquesta corba ha sigut poc estudiada fins ara i el seu càlcul és relativament fàcil. Per aquest motiu el present treball té com a objectiu l'optimització de l'energia i dels costos de bombament mitjançant l'ús de la CC. Per a complir amb l'objectiu, primer s'estudia el càlcul de la CC en xarxes d'aigua amb múltiples estacions de bombament, consums no depenents i dependents de la pressió, i sense tancs d'emmagatzematge. Posteriorment, es duu a terme l'optimització només des de la perspectiva energètica (cabal i altura de bombament). Per a açò es realitza la cerca de la distribució de cabals òptima entre les estacions de bombament que comporte a les CC òptimes. Es proposen dos mètodes: un de discret (M-D) i un altre continu (M-C). El M-D considera la distribució de cabals com una variable discreta. La distribució òptima s'obté d'un conjunt de solucions prèviament definides. En el M-C la distribució de cabals s'assumeix com a variable contínua. La solució òptima ve donada per l'ús d'un algorisme d'optimització. S'han usat els algorismes: Hooke-Jeeves i Nelder-Mead. El següent pas és l'optimització de costos d'operació (costos de bombament i costos de producció d'aigua). Per a açò es parteix del M-C i s'inclouen a més les tarifes d'energia, les tarifes de producció d'aigua i un criteri sobre el rendiment mínim esperat en les estacions de bombament. L'últim pas consisteix en l'optimització energètica i de costos en xarxes amb tancs. La inclusió de tancs implica la modificació del càlcul de la CC i per tant la metodologia d'optimització. En la funció de costos s'inclouen a més dels costos de bombament i de producció, costos de penalització per incompliment de pressions i de volums de reserva. En incloure's els tancs, incrementa el nombre de variables de decisió. Pel que, és necessari l'ús d'algorismes més potents. S'han usat el Differential Evolution i el Hybrid Algorithm. Aquest últim és una aportació afegida d'aquest treball. La metodologia d'optimització s'aplica a cinc xarxes de distribució: TF, Catinen, Coplaca, Anytown i Richmond. Els tancs només es consideren en les dues últimes xarxes. En el cas de la xarxa TF es realitza una demostració sense entrar en profunditat de la selecció de bombes a través de l'ús de les CC òptimes. No obstant açò, aquest pas està fora dels límits d'aquest treball. Tampoc es consideren condicions d'operació múltiples de la xarxa, ni la fiabilitat en el cas de la remoció de tancs o sistemes de bombament. No obstant açò, els resultats obtinguts evidencien que els sistemes de bombament operats usant la CC poden millorar els seus costos operatius fins a en un 12%. La metodologia proporciona informació sobre les estacions de bombament que representen majors estalvis enfront d'aquelles que són menys importants o innecessàries. A més, el mètode ha permès demostrar que millors condicions de bombament (baixes tarifes d'energia i alts rendiments) no sempre signifiquen menors costos d'operació. Finalment, alguns resultats mostren la possible utilitat del mètode per a optimitzar tant l'ús com la ubicació dels tancs d'emmagatzematge. / León Celi, CF. (2018). Optimisation of both energy use and pumping costs in water distribution networks with several water sources using the setpoint curve [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/107956 / TESIS

Over the last two decades, implementation of membrane bioreactors (MBRs) has increased due to their superior effluent quality and low plant footprint. However, they are still viewed as a high-cost option, both with regards to capital and operating expenditure (capex and opex). The present thesis extends the understanding of the impact of design and operational parameters of membrane bioreactors on energy demand, and ultimately whole life cost. A simple heuristic aeration model based on a general algorithm for flux vs. aeration shows the benefits of adjusting the membrane aeration intensity to the hydraulic load. It is experimentally demonstrated that a lower aeration demand is required for sustainable operation when comparing 10:30 to continuous aeration, with associated energy savings of up to 75%, without being penalised in terms of the fouling rate. The applicability of activated sludge modelling (ASM) to MBRs is verified on a community-scale MBR, resulting in accurate predictions of the dynamic nutrient profile. Lastly, a methodology is proposed to optimise the energy consumption by linking the biological model with empirical correlations for energy demand, taking into account of the impact of high MLSS concentrations on oxygen transfer. The determining factors for costing of MBRs differ significantly depending on the size of the plant. Operational cost reduction in small MBRs relies on process robustness with minimal manual intervention to suppress labour costs, while energy consumption, mainly for aeration, is the major contributor to opex for a large MBR. A cost sensitivity analysis shows that other main factors influencing the cost of a large MBR, both in terms of capex and opex, are membrane costs and replacement interval, future trends in energy prices, sustainable flux, and the average plant utilisation which depends on the amount of contingency built in to cope with changes in the feed flow.

In this thesis, the effect of pitch based optimisation was explored for a 80 turbine wind farm. Using a modified Jensen wake model and the Particle Swarm Optimisation (PSO) model, a pitch optimisation strategy was created for the dominant turbulence and atmospheric condition for the wind farm. As the wake model was based on the FLORIS model developed by P.M.O Gebraad et. al., the wake and power model was compared with the FLORIS model and a -0.090% difference was found. To determine the dynamic predictive capability of the wake model, measurement values across a 10 minute period for a 19 wind turbine array were used and the wake model under predicted the power production by 17.55%. Despite its poor dynamic predictive capability, the wake model was shown to accurately match the AEP production of the wind farm when compared to a CFD simulation done in FarmFlow and only gave a 3.10% over-prediction. When the optimisation model was applied with 150 iterations and particles, the AEP production of the wind farm increased by 0.1052%, proving that the pitch optimisation method works for the examined wind farm. When the iterations and particles used for the optimisation was increased to 250, the power improvement between optimised results improved by 0.1144% at a 222.5% increase in computational time, suggesting that the solution has yet to fully converge. While the solutions did not fully converge, they converged sufficiently and an increase in iterations gave diminishing results. From the results, the pitch optimisation model was found to give a significant increase in power production, especially in wake intensive wind directions. However, the dynamic predictive capabilities will have be improved upon before the control strategy can be applied to an operational wind farm.