Dissertations / Theses on the topic 'Heat storage – Economic aspects'

The purpose of this study was to determine if mild heat stress induced by wearing a wet suit while swimming in relatively warm water (25.4 ± 0.1°C) increases the risk of heat injury during the subsequent cycling and running stages. Specificlly, during an Olympic distance triathlon in a hot and humid environment (32°C & 65% RH). Five male triathletes randomly completed two simulated triathlons (Swim=30 min; Bike=40 km; Run=10 km) in the laboratory using a swimming flume, cycle ergometer, and running treadmill. In both trials, all conditions were identical, except for the swimming portion in which a full length, sleeveless neoprene wet suit was worn during one trial (WS) and a competitive brief swimming suit during the other (SS). The swim portion consisted of a 30 min standardized swim in which oxygen consumption (V02) was replicated, regardless of WS or SS. During the cycling and running stages, however, the subjects were asked to complete the distances as fast as possible. Core Temperature (T) was not significantly different between the SS and WS trials at any time point during the triathlon. However, mean skin temperature (TSk) and mean body temperature (Tb) were higher (p<0.05) in the WS at 15 (TSk=+4.1°C, Tb=+1.5°C) and 30 min (TSk=+4°C, Tb=+1.6°C) of the swim. These TSk and Tb differences were eliminated by 15 min of the cycling stage and remained similar (p>0.05) through the end of the triathlon. Moreover, there were no differences (p>0.05) in V02, heart rate (HR), rating of perceived exertion (RPE), or thermal sensation (TS) between the WS and SS. Additionally, no significant differences were found in cycling (SS=1:14:46 ± 2:48 vs. WS=1:14:37 ± 2:54 min), running (SS=55:40 ± 1:49 vs. WS=57:20 ± 4:00 min) or total triathlon times (SS=2:40:26 ± 1:58 vs. WS=2:41:57 ± 1:37 min). Therefore, the primary finding was that wearing a wet suit during the swimming stage of an Olympic distance triathlon in 25.4°C water does not adversely affect the thermal responses or the triathlete's ability to perform on the subsequent cycling and running stages.
School of Physical Education

Innovative methods for providing sustainable heating and cooling through thermal energy storage (TES) have gained increasing attention as heating and cooling demands in the built environment continue to climb. As energy prices continue to soar and systems reach their maximal capacity, there is an urgent need for alternatives to alleviate peak energy use. TES systems allow decoupling of energy production from energy utilization, both in location and in time. It is shown in this thesis that successful implementation of TES in the built environment alleviates peak energy load and reduces network expansion as well as the marginal energy production cost. This thesis analyzes phase change material (PCM) based TES systems in terms of material property characterization, numerical modeling and validation of thermal storage, as well as case specific techno-economic feasibility studies of system integration. The difficulties identified in latent heat TES design, such as heat transfer aspects, subcooling and identification of phase separation, have been analyzed through Temperature-History mapping and TES numerical modeling with experimental validation. This work focuses on the interdependency between resource availability, thermal charge/discharge power and storage capacity. In a situation where resource availability is limited, e.g. when using free cooling, waste heat or off-peak storage, the thermal power and storage capacity are strongly interrelated and should always be considered in unison to reach an acceptable techno-economic solution. Furthermore, when considering TES integration into an existing thermal energy distribution network, three adverse aspects are revealed in the Swedish case study: the single tariff system, the low-return temperature penalty, and the low storage utilization rate. These issues can be overcome through better adapted policies and optimized storage control strategies. Finally, despite the currently unfavorable conditions in the Swedish energy system, it is shown that TES has the potential to mitigate climate change through greenhouse gas emission reduction by displacing fossil-fuel based marginal thermal energy production.
QC 20110629
Cold Thermal Energy Storage

The liberalization of electricity markets and a growing penetration of renewables is changing operation of electrical grids. The boundary conditions for the operation of conventional power plants are changing and, as such, an improved understanding of the varying loads and prices on the electricity grid is required to assess the performance of emerging combined cycle gas turbine (CCGT) concepts and to further optimize their design for these new markets in the pursuit of increasing their profitability, especially when considering combined heat and power (CHP). To increase the flexibility of CCGT-CHP plants, three new plant layouts have been investigated by integrating different storage concepts and heat pumps in key sections of the traditional plant layout. The present study analyses the influence that market has on determining the optimum CCGT-CHP plant layout that maximizes profits (in terms of plant configuration, sizing and operation strategies) for a given location nearby Turin, Italy, for which hourly electricity and heat prices, as well as meteorological data, have been gathered. A multi-parameter approach for design and operation was followed using KTH’s and EPS’ techno-economic modeling tool DYESOPT. Results are shown by means of a comparative analysis between optimal plants found for each layout and the state-of-the art CCGT-CHP. It is shown that a plant configuration in which a cold storage unit is integrated together with a heat pump at the inlet of the gas turbine unit increases the net present value of the plant by approximately 0.3% when compared against conventional plant layouts. Using the same concept with a heat pump alone can improve lifetime profitability by 1.6%. A layout where district heating supply water is preheated with a combination of a heat pump with hot thermal tank increases plant profitability by up to 0.5%. This work has been performed as part of the PUMP-HEAT project, an EU Horizon 2020 research project in which KTH collaborates with other 13 stakeholders including industry and research institutions. The results will directly influence future work of the project.

Though economically favorable when compared to other renewable energy storage technologies, thermal energy storage systems for concentrating solar thermal power (CSP) plants require additional cost reduction measures to help transition CSP plants to the point of grid-parity. Thermocline packed bed storage is regarded as one potential low cost solution due to the single tank requirement and low cost storage media. Thus sensible heat storage (SHS) and latent heat storage (LHS) packed bed systems, which are two thermocline varieties, are frequently investigated. LHS systems can be further classified as single phase change material (PCM) systems or cascaded systems wherein multiple PCMs are employed. This study compared the performance of SHS, single PCM, and cascaded PCM direct storage systems under the conditions that may be encountered in utility-scale molten salt CSP plants operating between 565°C and 288°C. A small-scale prototype SHS packed bed system was constructed and operated for use in validating a numerical model. The drawbacks of the latent heat storage process were discussed, and cascaded systems were investigated for their potential in mitigating the issues associated with adopting a single PCM. Several cascaded PCM configurations were evaluated. The study finds that the volume fraction of each PCM and the arrangement of latent heat in a 2-PCM and a 3-PCM system influences the output of the system, both in terms of quality and quantity of energy. In addition to studying systems of hypothetical PCMs, real salt PCM systems were examined and their selection process was discussed. A preliminary economic assessment was conducted to compare the cost of SHS, single-PCM LHS, cascaded LHS, and state-of-the-art 2-tank systems. To the author's knowledge, this is the first study that compares the cost of all three thermocline packed bed systems with the 2-tank design. The SHS system is significantly lower in cost than the remaining systems, however the LHS system does show some economic benefit over the 2-tank design. If LHS systems are to be viable in the future, low cost storage media and encapsulation techniques are necessary.

The objective of this thesis was to assess the market opportunities for two novel Carnot battery system solutions, one supplying power and low temperature heat as well as a system supplying medium temperature heat exclusively. To fulfill the objective, a methodology was developed and implemented to investigate the market potential, further two techno-economic models were developed and utilized to investigate the performance of such Carnot battery solutions. Based on the market review four industrial sectors were identified as most interesting and the geographical scope was confined to Europe. Further, case studies were developed to mimic two different sizes of manufacturing plants, a small and large, for the identified sectors. The cases were then implemented to the techno-economic analysis to compare the performance of a new Carnot battery system against the conventional energy solutions. The identified market offers a vast opportunity for incorporating Carnot battery solutions to meet the industrial sectors requirements, both from a technical and market size perspective. The market review combined with the techno-economic analysis indicates that the heat market is interesting as long as fuel, power grid costs and industrial operations are at the ideal level. For the Carnot battery system supplying both power and heat, it was found that yearly cost savings in the range of 10-15 % could be achieved for the identified market. The added value of incorporating heat generation and surplus power from PV had a strong effect on the business case. Through sensitivity analysis it was approximated that locations in central/south Europe with global horizontal irradiance (GHI) above 1500 kWh/m2 would benefit from the solution. For the Carnot battery system supplying medium temperature heat it was found that solutions would struggle with feasibility for the given market conditions. Through sensitivity it was found that locations with GHI higher than 2100 kWh/m2 would benefit from the solution. For both models it was found that the hybrid solution, Carnot battery combined with on-site PV, yields the most feasible solution for the end user, compared to charging the Carnot storage system from the power grid. Both models were sensitives to changes in energy cost for operating the old conventional system as well as operations times of the industries. The availability of space is a major constraint to implement Carnot battery solutions, as both the Carnot battery as well as PV plant require substantial space. It was found through literature and interviews that industries with close proximity to end customer and which faces pressure to decarbonize, may be most interesting to target, as for e.g. the Food and beverage sector.
Syftet med denna uppsats var att undersöka marknadspotentialen för två stycken Carnot batterisystem, ett system som generar både el och låg tempererad värme och ett som endast generar medel tempererad värme. För att uppnå målet så utvecklades och implementerades en metod för att undersöka marknadspotentialen, vidare så utvecklades och användes två tekno-ekonomiska modeller för att undersöka prestandan för de två Carnot lösningarna. Baserat på marknadsundersökningen så identifierades fyra industriella sektorer som mest intressanta och baserat på dem begränsades omfattningen av studien till Europa. Från marknadsgenomsökningen och de identifierade industriella sektorerna skapades två olika profiler för att representera en liten och stor industri för de identifierade sektorerna. Profilerna användes som utgångspunkt för den tekno-ekonomiska analysen för att jämföra prestandan hos ett nytt Carnot batterisystem mot konventionella energilösningar. Den identifierade marknaden erbjuder en stor möjlighet för att integrera Carnot batterilösningar för att möta industrisektorns krav, både ur ett tekniskt perspektiv och med tanke på marknadensstorleken. Marknadsundersökningen kombinerat med tekno-ekonomiskanalysen indikerar att värmemarknaden för industrier är intressant så länge bränsle- och elkostnader samt drifttiden är i rättnivå. Resultat från analysen tyder på att Carnot batterilösningar, som generar både el och värme, kan skapa energikostnadsbesparingar runt 10–15 % för den identifierade marknaden. Värdet av att addera kassaflöden från överskotts el från solcellerna samt värmegenerering har en stark påverkan på resultaten. Från en känslighetsanalys gick det att identifiera centrala/södra Europa som platser med tillräcklig solinstrålning (runt 1500 kWh/m2) för att dra nytta av ett Carnot batteri. För Carnot batterisystemet som endast producerar medel tempererad värme så skapas inga energikostandsbesparingar för slutanvändaren för den analyserade marknadsförutsättningarna. Genom en känslighetsanalys gick det att fastställa att hög solinstrålning krävs (över 2100 kWh/m2) för att slutanvändaren ska skapa några besparingar med systemet. För båda modellerna generade en hybridsystemlösning med både Carnot batteri samt lokal solcellsanläggning de bästa resultaten, jämfört med om systemet skulle laddas från elnätet. Båda modellerna är känsliga mot förändringar i energikostnader, värme eller el, för det konventionella systemet samt lägre drifttid. Vidare så är tillgänglig yta en annan restriktion som både kan hindra implementeringen av Carnot batteriet samt också solcellsanläggningen. Både litteraturstudien och de genomförda intervjuerna tyder på att industrier som har nära kontakt med slutkonsumenten och som har krav på att reducera sin miljöpåverkan, är en intressant användare av ett Carnot batterilösning, som exempelvis livsmedelsindustrin.

The International Energy Agency’s Global Status Report 2017 estimates that existing buildings must undergo deep energy renovations, which reduce the energy intensity of buildings by 50% - 70% in order to achieve the “Beyond 2°C” scenario [1]. Many buildings in Bitola, The Republic of North Macedonia, will need considerable upgrades to meet these goals. Among them, health care facilities and education centers have the greatest potential, with energy savings that could reach 35 to 40% [2]. PHI Clinical Hospital Bitola is the largest health care facility in the southwestern region of North Macedonia with a capacity of 500 beds, providing care to almost 300.000 patients annually. It has a heating system based on heavy fuel oil, and an inefficient distribution system which has not been upgraded since the 1970s. There is no centralized ventilation or cooling systems, making it necessary to open and close windows in order to regulate the indoor temperature and generate natural ventilation. This study aims to replace the use of heavy fuel oil (HFO), reduce building related GHG emissions, and increase the primary renewable energy fraction of PHI Clinical Hospital Bitola, by investigating a replacement energy system using heat pumps and solar energy. Special consideration is given to increasing the level of comfort of patients and improving the safety of the indoor environment. Space conditioning, domestic hot water, and electricity demands for three critical buildings are considered in Polysun over a 1-year period. The costs and benefits of technologies including air and ground source heat pumps, solar photovoltaics, and ice thermal energy storage are analyzed. It is determined which of these technologies can be implemented in an energy and cost-efficient manner in the Republic of North Macedonia, thus contributing to the reduction of building related greenhouse gas emissions and other pollutants that contribute to poor air quality. Ground source heat pumps perform superior to air source heat pumps, however, the total life cycle costs of ground source heat pump systems are much higher than air source heat pump systems, making the marginal gains in the technical performance not worth the investment in a borehole field. When using ice thermal energy storage within the cooling and domestic hot water systems the benefits of improved heat pump performance and reduced electricity consumption are not observed. The configuration of thermal storage tested here uses the domestic hot water system to withdraw heat from the thermal storage tank, creating ice, which is then used to decrease the need for cooling using the chiller. However, the cooling load is much larger than the hot water demand, and so any ice generated in the tank is depleted within the first few days of cooling. Many other configurations and control strategies for thermal storage exist which could be the subject of further research. When selecting a renewable energy system that could replace the current HFO boiler in the hospital, the results of this study suggest that an air source heat pump system with solar PV is the recommended solution. For buildings 1 and 2, the final results achieved a primary renewable energy fraction of 62%, a GHG emissions savings of 840 tons of CO2eq equating to a 26% reduction, coming at a capital cost of nearly 2,7 million €, and reducing annual energy expenses by 47%. For building 4 the final system delivers a primary renewable energy fraction of 64%, GHG emissions savings of 109 tons CO2eq or 17%, while costing 0,67 million € in capital expenses and lowering annual energy expenses by 50%.
Den internationella energi byråns globala status rapport 2017 uppskattar att existerande byggnader måste undergå djupgående energi renovationer, som ska reducera byggnadernas energiintensitet med 50% - 70% för att uppnå i scenariot “Beyond 2°C” [1]. Många byggnader i Bitola (Republiken av nora Makedonien), kommer att behöva betydande uppgraderingar för att uppfylla dessa mål. Bland dem har hälsovårdsanläggningar och utbildningscenter den största potentialen, med energi besparingar där dessa kan uppnå 35% till 40% [2]. PHI Kliniskt Sjukhus Bitola är den största sjukvårdsanläggningen i den sydvästra regionen av Nora Makedonien med en kapacitet på 500 sängplatser, som ger vård till nästan 300.000 patienter årligen. Det nuvarande värmesystemet är baserat på tung eldningsolja och ett ineffektivt distributionssystem som inte har uppdaterats sedan 1970-talet. Det finns inga centraliserade ventilations- och kylsystem, vilket gör det nödvändigt att öppna och stänga fönster för att reglera inomhustemperaturen och generera naturlig ventilation. Denna studie syftar till att ersätta användningen av tung eldningsolja, minska byggnadsrelaterade växthusutsläpp och öka den primära förnyelsebara energifraktionen av Kliniskt Sjukhus Bitola. Genom att undersöksöka ett ersättande energisystem med värmepumpar och solenergi. Särskild hänsyn tas till öka patienternas komfort och förbättra säkerheten i inomhusmiljön. Värme och kyla, varmvatten och el-krav för tre kritiska byggnader betraktas i Polysun under en 1- års period. Kostnaderna och fördelarna med tekniken inklusive luft och markvärmepumpar, solceller och termisk energilagring analyseras. Det fastställs vilken av dessa tekniker som kan implementeras på ett energi- och kostnadseffektivt sätt i Republiken av nora Makedonien, vilket bidrar till att minska byggnadsrelaterade växthusgasutsläpp och andra föroreningar som kan bidra till dålig luftkvalitet. Markvärmepumpar har högre prestanda än luftvärmepumpar, men de totala livscykelkostnaderna för ett markvärmepumpsystem är mycket högre än för ett luftvärmepumpsystem. Vilket gör den marginella vinsterna för den tekniska prestandan inte värda investeringen av ett borrhåls fält. Vid användning av is som termisk energilagring och kylning och varmvattensanläggningar, tog ingen hänsyn till fördelarna med en förbättrad värmepumps prestanda och minskad elförbrukning. Konfigurationen av termisk lagring som testas här använder det inhemska varmvattensystemet för att ta bort värme från den termiska lagringstanken, vilket skapar is som sedan används för att minska behovet av nedkylning av byggnaden. Kylbelastningen är emellertid mycket större än varmvattenbehovet. Vilket betyder att all is som genereras i tanken används upp efter några dagar av kylning. Många andra konfigurationer och styrstrategier för termisk lagring finns och kan vara till ändamål för framtida forskning. När val av ett förnybart energisystem görs som ska kunna ersätta den nuvarande tung eldningsolja pannan på sjukhuset antyder resultatet av denna studie att ett värmepumpsystem med luftkälla och sol-PV är den rekommenderade lösningen. För byggnad 1 och 2 uppnådde det slutliga resultatet en primär förnyelsebar energifraktion på 62%, vilket skulle innebära en besparing av växthusgasutsläpp med 840 ton CO2 ekvivalenter. Vilket motsvarar en minskning med 26%, med en kapitalkostnad på nästan 2,7 miljoner €. Samt minskade årliga energikostnader med 47%. För byggnad 4 levererar det slutliga systemet en primär förnybar energifraktion på 64%, med en -5- besparing av växthusutsläpp på 109 ton CO2 ekvivalenter eller 17%. Medan det kostar 0,67 miljoner € i kapitalutgifter och sänker den årliga energikostnaden med 50%.

This thesis investigates the feasibility and benefits of integrating Thermochemical heat Storage (THS) into a CHP (Combined Heat and Power) plant. A case study is done for the CHP-plant in Sala, Sweden, with a maximum heat output of 20.9 MW and maximum electricity output of 9.6 MW. The THS type considered is calcium oxide in a hydroxide system. The fluctuations in electricity price for years 2020, 2030 and 2040 are considered and low-price electricity is used as a charging source for THS. During charging the superheated steam (endothermic reaction) is used to cover some of the district heating demand. The high temperature discharge from the THS is used as reheat in the Rankine cycle. The operations are modeled in Ebsilon and optimization is done in MATLAB using genetic algorithm with the objective to achieve maximum annual revenue. The results suggest that it is not feasible to introduce THS with electricity as a charging source in year 2020, but in 2030 and 2040 THS shows promising potential. The biggest increase in revenue comes from reduced fuel consumption, and, to a lesser extent, increased income from electricity. It is concluded that Calcium hydroxide is a promising candidate for integration into CHP during large electricity price fluctuation. The main drivers for the feasibility of this combination are high fuel price and large fluctuations of electricity price.

The passage of the Hazardous and Solid Waste Amendments of 1984 (HSWA) and the Superfund Amendments and Reauthorization Act of 1986 (SARA) amended subtitle I of the Resource Conservation and Recovery Act (RCRA). RCRA now requires the Environmental Protection Agency (EPA) to promulgate regulations applicable to all owners and operators of underground storage tanks (USTs) containing petroleum products, and substances listed as hazardous in the Comprehensive Environmental Response Compensation and Liability Act, but not regulated as hazardous waste under RCRA subtitle C. On 17 April 1987, EPA issued proposed regulations for leak detection, leak prevention, financial responsibility and corrective action for USTs containing regulated substances. Concern over potential adverse economic impacts caused by UST regulation has centered on the retail motor fuel market, due primarily to its large size and relatively large number of small businesses. While public and private studies have been conducted concerning the economic impact of UST regulation on the retail motor fuel market, a need for additional research is indicated. This thesis presents the findings to date of a study examining the economic impacts that alternative UST regulatory programs would have on the retail motor fuel market in the United States, with emphasis, where possible, on this market in Virginia. The market is broken into five segments based on similar economic and management characteristics. The segment most likely to contain significant numbers of firms that could be forced out of business due to UST regulation is identified. Proposed minimum federal UST regulations are described and relevant regulatory costs are presented. Three additional UST regulatory programs are developed representing varying degrees of stringency relative to the proposed minimum federal regulations. Case studies of firms located in the vulnerable segment of the retail motor fuel market identified earlier are analyzed in terms of the effect that alternative UST regulations would have on yearly owner remuneration (which is defined to include both the return to the owner as a factor of production and the profit remaining after all returns to land, capital, and labor have been paid). Hypothetical firms with profit levels determined by EPA as average for two segments of the regulated community are analyzed in a similar fashion to reflect the effect of alternative UST regulations on profits.
Master of Urban and Regional Planning

Thesis (MScEng)--Stellenbosch University, 2012.
ENGLISH ABSTRACT: The focus of this project was on the potential application of waste heat recovery and utilisation (WHR&U) systems in pebble bed modular reactor (PBMR) technology. The background theory provided in the literature survey showed that WHR&U systems have attracted the attention of many researchers over the past two decades, as using waste heat improves the system overall efficiency, notwithstanding the cost of extra plant. PBMR waste heat streams were identified and investigated based on the amount of heat rejected to the environment. WHR&U systems require specially designed heat recovery equipment, and as such the used and/or spent PBMR fuel tanks were considered by the way of example. An appropriately scaled system was designed, built and tested, to demonstrate the functioning of such a cooling system. Two separate and independent cooling lines, using natural circulation flow in a particular form of heat pipes called thermosyphon loops were used to ensure that the fuel tank is cooled when the power conversion unit has to be switched off for maintenance, or if it fails. A theoretical model that simulates the heat transfer process in the as-designed WHR&U system was developed. It is a one-dimensional flow model assuming quasi-static and incompressible liquid and vapour flow. An experimental investigation of the WHR&U system was performed in order to validate the theoretical model results. The experimental results were then used to modify the theoretical heat transfer coefficients so that they simulate the experiments more accurately. Three energy conversion devices, the dual-function absorption cycle (DFAC), the organic Rankine cycle (ORC) and the Stirling engine (SE), were identified as suitable for transforming the recovered heat into a useful form, depending on the source temperatures from 60 ºC to 800 ºC. This project focuses on a free-piston SE with emphasis on the thermo-dynamic performance of a SE heat exchanger. It was found that a heat exchanger with a copper woven wire mesh configuration has a relatively large gas-to-metal and metal-to-liquid heat transfer area. Tube-in-shell heat exchanger configurations were tested, with the working fluid flowing in ten copper inner pipes, while a coolant flows through the shell tube. A lumped parameter model was used to describe the thermo-fluid dynamic behaviour of the SE heat exchanger. In order to validate the theoretical results, a uni-directional flow experimental investigation was performed. The theoretical model was adjusted so that it simulated the SE heat exchanger. It was found that after this correction the theoretical model accurately predicts the experiment. Finally, a dynamic analysis of the SE heat exchanger experimental set-up was undertaken to show that, although vibrating, the heat exchanger setup assembly was indeed acceptable from a vibrational and fatigue point of view.
AFRIKAANSE OPSOMMING: Die hoofoogmerk met hierdie projek was die moontlike aanwending van afvalhitteherwinningen- benutting-(WHR&U-) stelsels in modulêre-gruisbedreaktor-(PBMR-) tegnologie. Agtergrondteorie in die literatuurondersoek toon dat WHR&U-stelsels al menige navorser se belangstelling geprikkel het, hetsy vanweë die moontlike ekonomiese voordele wat dit inhou óf vir besoedelingsvoorkoming, bo-en-behalwe die koste van bykomende toerusting. Die PBMRafvalhittestrome is ondersoek en bepaal op grond van die hoeveelheid hitte wat dit na die omgewing vrystel. Om in die prosesbehoeftes van WHR&U-stelsels te voorsien, moet goed ontwerpte, doelgemaakte hitteherwinningstoerusting in ʼn verkoelings- en/of verhittingsproses gebruik word, dus is die PBMR as voorbeeld gebruik vir die konsep. ʼn Toepaslik geskaleerde WHR&U-stelsel is dus ontwerp, gebou en getoets om die geldigheid van die stelselontwerp te toon. Twee onafhanklike verkoelingslyne, wat van natuurlike konveksie gebruik maak, in die vorm van hitte-pype of termoheuwel lusse, was gebruik om te verseker dat verkoeling verskaf word wanneer die hoof lus breek of instandhouding nodig hê. ʼn Teoretiese model is ontwikkel wat die hitteoordragproses in die ontwerpte WHR&U-stelsel simuleer. Dié model was ʼn eendimensionele vloeimodel wat kwasistatiese en onsamedrukbare vloeistof- en dampvloei in die WHR&U-stelsel-lusse veronderstel. ʼn Eksperimentele ondersoek is op die WHR&U-stelsel uitgevoer ten einde die teoretiese model se resultate te bevestig. Die eksperimentele resultate was dus geneem om die teoretiese hitteoordragkoëffisiënte aan te pas sodat dit die eksperimente kon simuleer. Drie energieomsettingstoestelle, naamlik die dubbel funksie absorpsie siklus (DFAC), die organiese Rankine siklus (ORC) en die Stirling enjin (SE), is as geskikte toestelle uitgewys om die herwonne hitte op grond van brontemperature tussen 60 ºC en 800 ºC in ʼn bruikbare vorm om te sit. Hierdie tesis het op vryesuier-SE’s gekonsentreer, met klem op die hitteruiler. Meer bepaald is die termodinamiese werkverrigting van ʼn SE-hitteruiler ondersoek. Daar is bevind dat ʼn hitteruiler met ʼn geweefde koperdraadmaas-samestelling oor ʼn betreklik groot gas-totmetaal- en metaal-tot-vloeistof-oordragoppervlakte beskik. Die verhitter en verkoeler is in ʼn buis-in-mantel-vorm ontwerp, met die werksvloeistof wat deur tien koperbinnepype vloei en ʼn koelmiddel deur die mantelbuis. ʼn Saamgevoegde-parameter-model is gebruik om die termodinamiese gedrag van die SEhitteruiler te beskryf. Ten einde die teoretiese resultate te bevestig, is ʼn eenrigtingvloeiproefondersoek uitgevoer. Die teoretiese model is aangepas sodat dit die SE-hitteruiler kon simuleer. Ná die nodige verstellings is daar bevind dat die teoretiese model die proefneming akkuraat voorspel. Laastens was ʼn dinamiese ontleding van die SE-hitteruiler ook onderneem om te toon dat, hoewel dit vibreer, die hitteruiler proef samestel inderdaad veilig is.

Several CO2 transcritical booster systems in supermarkets use the potential of integrating geothermal storage, enabling subcooling during warm climate conditions as well as being a heat source during cold climate conditions. First of all, field measurements of one of these systems located in Sweden were analysed with particular focus on the heat-recovery performance. The best theoretical operational strategy was compared to the one really implemented and the differences in the annual energy usage were assessed through modelling. The results show that an alternative to the best theoretical operational strategy exists; heat can be extracted from the ground while low-temperature heat is rejected by the gas cooler. Such an alternative strategy has important technical advantages with a negligible increment of the energy usage. In the second part of this work, the benefits of geothermal subcooling were evaluated. Applying the BIN hours method, it was demonstrated that this system is expected to save on average roughly 5% of the total power consumption, in Stockholm’s climate. The models utilized for the winter and summer season were combined to find the relationship between geothermal storage size and annual energy savings. In this way, it was possible to calculate the present value of the operational savings for the study case. Furthermore, a general methodology for assessing the economic feasibility of this system solution is presented. Finally, several scenarios were investigated to produce parametric curves and to perform a sensitivity analysis. Comparing the results with the typical Swedish prices for boreholes, the cases where this system solution is economically justified were identified. These are supermarkets with a Heat Recovery Ratio (HRR) higher than the average. For examples, supermarkets supplying heat to the neighbouring buildings (considering the Stockholm’s climate, systems with an annual average HRR of at least 70%). Relying only on savings from subcooling was found to be not enough to justify a geothermal storage, a not-negligible amount of heat must be extracted in winter. Finally, some interesting concepts and alternatives to a geothermal integration are presented to point out relevant future work.

This study describes a simulation-based approach for informing the incorporation of Phase Change Materials (PCMs) in buildings designed to the "Passive House" standard. PCMs provide a minimally invasive method of adding thermal mass to a building, thus mitigating overheating events. Phase change transition temperature, quantity, and location of PCM were all considered while incrementally adding PCM to Passive House simulation models in multiple climate zones across the United States. Whole building energy simulations were performed using EnergyPlus from the US Department of Energy. A prototypical Passive House with a 1500 Watt electric heater and no mechanical cooling was modeled. The effectiveness of the PCM was determined by comparing the zone-hours and zone-degree-hours outside the ASHRAE defined comfort zone for all PCM cases against a control simulation without PCM. Results show that adding PCM to Passive Houses can significantly increase thermal comfort so long as the house is in a dry or marine climate. The addition of PCM in moist climates will not significantly increase occupant comfort because the majority of discomfort in these climates arises due to latent load. For dry or marine climates, PCM has the most significant impact in climates with lower cooling degree-days, reducing by 93% the number of zone-hours outside of thermal comfort and by 98% the number of zone-degree-hours uncomfortable in Portland, Oregon. However, the application of PCM is not as well suited for very hot climates because the PCM becomes overcharged. Only single digit reductions in discomfort were realized when modeling PCM in a Passive House in Phoenix, Arizona. It was found that regardless of the climate PCM should be placed in the top floor, focusing on zones with large southern glazing areas. Also, selecting PCM with a melt temperature of 25°C resulted in the most significant increases in thermal comfort for the majority of climates studied.

Els edificis d’energia neta poden ser entesos com a edificis, que durant un temps determinat generen tanta energia com consumeixen. Ja sigui des del punt de vista de l’oferta o el consum, la disponibilitat d’energia està relacionada amb alguns aspectes bàsics, com ara la font (s), la conversió, la distribució, l’ús, el malbaratament, l’optimització, l’eficiència i l’autonomia. Aquests temes revelen la complexitat del tema de l'energia i justifiquen l'atenció especial que li dóna la comunitat acadèmica. Per obtenir resultats tangibles en l'anàlisi d'aquests sistemes, en el nostre estudi ens centrem en la modelització i optimització de solucions energètiques aplicades a edificis o sistemes similars. D'altra banda, el període de temps dels objectes analitzats es va estendre fins al seu període de cicle de vida previst. Es van establir els objectius principals com: - Verificar i analitzar l’estat de la tecnologia de les energies renovables per a edificis i actius construïts i l’aplicabilitat de l’anàlisi de costos del cicle de vida a aquests temes; - Configurar models reproductibles d’edificis i les seves principals càrregues elèctriques, mitjançant eines d’enginyeria de processos assistits per ordinador, per procedir a simulacions i optimització, considerant-se com a font d’energia primària l’energia solar; - Quantificar, utilitzant estudis de casos reals i hipotètics, els beneficis de les solucions proposades, amb l'objectiu de realitzar tota l'avaluació de la sostenibilitat de la vida mitjançant la reducció de tot el cost del cicle de vida;
Los edificios de energía de red cero pueden entenderse como edificios, que durante un tiempo dado generan tanta energía como consumen. O bien, desde el punto de vista del suministro o el consumo, la disponibilidad de energía está relacionada con algunos problemas básicos, como las fuentes, la conversión, la distribución, la utilización, el desperdicio, la optimización, la eficiencia y la autonomía. Estos problemas revelan la complejidad del tema de la energía y justifican la atención especial que le presta la comunidad académica. Para obtener resultados tangibles en el análisis de estos sistemas, en nuestro estudio nos centramos en el modelado y la optimización de soluciones energéticas aplicadas a edificios o sistemas similares. Por otro lado, el período de tiempo de los objetos analizados se extendió a su período de ciclo de vida esperado. Los objetivos principales se establecieron como: - Verificar y analizar el estado de la técnica de las soluciones de energía renovable para edificios y activos construidos y la aplicabilidad del análisis de costos de ciclo de vida a estas cuestiones; - Configure modelos reproducibles de edificios y sus principales cargas eléctricas, a través de herramientas de Ingeniería de Procesos Asistidos por Computadora, para proceder a simulaciones y optimización, considerando como fuente de energía primaria la energía solar;
Net-zero energy buildings can be understood as buildings, that for a given time, generate as much energy as they consume. Either, from the point of view of supply or consumption, energy availability is related to some basic issues such as source (s), conversion, distribution, utilization, waste, optimization, efficiency and autonomy. These issues reveal the complexity of the subject of energy and justify the special attention given to it by the academic community. To obtain tangible results in the analysis of these systems, in our study we focus on the modelling and optimization of energy solutions applied to buildings or similar systems. On the other hand, the time frame of the analysed objects was extended to their expected life cycle period. The main objectives were stablished as: - Verify and analyse the state-of-the-art of renewable energy solutions for buildings and constructed assets and the applicability of life cycle costing analysis to these issues; - Configure reproducible models of buildings and their main electrical loads, via Computer Aided Process Engineering tools, to proceed simulations and optimization, considering as primary energy source solar energy; - Quantify, using real-life and hypothetical case studies, the benefits of the proposed solutions, aiming the whole life sustainability assessment through the reduction of the whole life cycle costing; and - Guarantee the reproducibility of the models and main general results of this study and make them public, to contribute with their applicability and further researches.

O objetivo deste trabalho foi analisar o armazenamento do arroz no Brasil, propondo modelos para tomada de decisão quanto à formação de estoques. Uma vez conhecidos estes modelos é possível analisar previamente as intervenções pretendidas pelo governo. Para tanto se partiu da hipótese de que é possível representar o mercado de arroz no Brasil através de um modelo dinâmico de expectativas racionais capaz de captar o efeito da importação do produto e de algumas políticas de sustentação de preço ao produtor adotadas pelo governo brasileiro. A proposta metodológica para a estimação do modelo segue a abordagem de programação dinâmica. Foram desenvolvidos algoritmos que representam o mercado de arroz no Brasil em uma situação de mercado fechado sem intervenção do governo, mercado aberto sem intervenção do governo, mercado fechado com intervenção do governo via Prêmio de Escoamento do Produto - PEP, mercado fechado com intervenção do governo via Aquisição do Governo Federal - AGF mercado aberto com intervenção do governo via PEP, mercado aberto com intervenção do governo via AGF. Os métodos utilizados para solução exigem que sejam conhecidos as funções de demanda e oferta de área, o custo unitário de armazenamento, a taxa anual de juros, a distribuição de probabilidades das variáveis aleatórias (produtividade e choques de demanda) e os preços de importação e mínimos (quando for o caso). Os preços esperados de mercado na situação de mercado aberto com intervenção via PEP foram ligeiramente inferiores ao preço de mercado sem intervenção, porém o preço recebido pelo agricultor foi ligeiramente maior. Isto significa que parte dos recursos da PEP é apropriada pelo produtor e parte pela indústria. Os resultados do modelo aberto com AGF demonstram que os preços para o comprador ficam acima do encontrado para o modelo sem intervenção do governo. Outro resultado encontrado foi que o nível de preços mínimos praticado nos últimos anos não tem sido suficientemente elevado a ponto de promover mudanças significativas no equilíbrio de mercado interno.
The aim of this study was to analyze rice storage in Brazil, proposing a model for decision taking regarding stock formation. Once these models are known it is possible to previously analyze the government interventions. Thus, the study was based on the hypothesis that it is possible to represent the rice market in Brazil through a dynamic model of rational expectations able to analyze the product importation effect and some policies of price support to the producer adopted by the Brazilian government. The methodological proposal for estimating the model follows the dynamic programming approach. It was developed algorithms which represent the rice market in Brazil in a situation of closed market without the government intervention, open market without government intervention, closed market with the government intervention through PEP (Prêmio de Escoamento do Produto – Prize for Product Outletting), closed market with the government intervention through AGF (Aquisição do Governo Federal – Federal Government Acquisition), open market with the government intervention through PEP, open market with government intervention through AGF. The methods used for the solution require that it be known the demand and supply functions for the area, the unit storage cost, the annual interest rate, the distribution of probabilities of random variables (productivity and demand shocks), importation and minimum (whenever is the case) prices. The expected market prices in the situation of open market with intervention through PEP were slightly lower than to the market price without intervention, however the price received by the grower was a little higher. It means that part of the PEP resources is allotted by the grower and part by the industry. The results of the open model with AGF show that the prices for the buyer are higher than those found in the model without government intervention. Another result was that the level of minimum prices practiced over the last years has not been adjusted to the point to promote significant changes in the balance of the domestic market.

This diploma’s thesis analyzes the possibility of accumulation of thermal power plants in the Czech Republic. The thesis is divided into several parts. The first part describes the different types of storage power plants, the historical development of power storage for compressed air and the appropriateness of their location. The second part is devoted to the design of storage power plant for compressed air in South Moravia. In the next chapter, a calculation is made of all equipment storage power plant, including turbo-compressor, combustion chamber, combustion turbines, the volume of storage tanks and two heat exchangers. The last part is the economic analysis of the return on investment of such a project.

The thesis deals with energy simulation of a solar energy system in a low-energy family house with warm-air heating. The simulations performed resulted in the assessment of the energy contribution of four solar systems with different types of collectors. The profitability and return of investment for the particular system have been evaluated based on investment costs and the savings gained. The theoretical part includes an introduction to the solar energy field, solar panel systems and the passive house concept. The practical part is devoted to description of the simulated object models as used in the TRNSYS environment, the simulation results evaluation along with the assessment of the economic return on investment. The conclusion recommendations regarding a suitable type and size of the solar panel with respect to the economic criteria chosen are given.

Les travaux présentés dans ce manuscrit portent sur l’optimisation d’une chaufferie collective multi-énergie en l’équipant d’un système de stockage thermique de type hydro-accumulation. L’efficacité de ce dernier dépend de sa capacité à conserver son énergie initiale. Ainsi, pour minimiser les pertes thermiques, le système de stockage doit être correctement isolé. Un modèle de ballon d’hydro-accumulation stratifié est développé et validé expérimentalement. Une étude paramétrique est menée afin d’étudier l’impact, sur les pertes thermiques, de paramètres géométriques et météorologiques. Ensuite, une approche de dimensionnement, fondée sur une stratégie de gestion séquentielle et une étude paramétrique est proposée. Plusieurs critères énergétiques et économiques peuvent ainsi être évalués pour différents volumes de stockage thermique. L’approche de dimensionnement proposée a été appliquée à plusieurs sites exploités par Cofely GDF-Suez, notre partenaire industriel. Les résultats obtenus montrent que le dimensionnement optimal du système de stockage et la gestion intelligente du procédé permettent d'optimiser le fonctionnement d’un site. Des économies énergétiques et financières importantes peuvent ainsi être réalisées. La stratégie de gestion séquentielle proposée n’anticipe pas les besoins du réseau de chaleur. C’est pourquoi une stratégie fondée sur la commande prédictive (MPC pour Model Predictive Control) est susceptible d’améliorer le fonctionnement et les performances d’une chaufferie collective équipée d’un système d’hydro-accumulation. Afin de mettre en œuvre un tel contrôleur, la puissance thermique demandée par le réseau de chaleur doit être correctement prédite. Par conséquent, une méthode de prédiction a été développée. Elle s’appuie sur une analyse multi-résolution par transformée en ondelettes discrète et sur l’utilisation de réseaux de neurones artificiels de type perceptron multicouche. La stratégie séquentielle (non prédictive) et la stratégie prédictive ont été appliquées à une chaufferie collective mixte située dans une commune du nord de la France. Pour ce cas d’étude, la stratégie prédictive est plus efficace. De plus, les résultats montrent que, quelle que soit la stratégie utilisée, équiper la chaufferie d’un système d’hydro-accumulation correctement dimensionné est un investissement rentable. Il permet de minimiser la consommation d’énergie fossile et, par conséquent, le coût économique et les émissions de CO2
The present work deals with optimizing a multi-energy district boiler by adding to the plant a thermal water storage tank. The effectiveness of such a system depends on how long the stored energy can be kept without considerable degradation. The storage tank should be properly insulated to reduce the rate of heat loss. Thus, firstly, a stratified water thermal storage model is developed and experimentally validated. A parametric study is carried out to determine the influence of geometric and meteorological parameters on heat loss. Next, a reliable sizing method based on a sequential management strategy and a parametric study is proposed. Various energy and economic criteria have been evaluated for a range of thermal storage sizes. The proposed methodology has been applied to many plants managed by Cofely GDF-Suez, our industrial partner. Results highlight the ability of a thermal storage tank (optimally sized and managed) to improve the operation of a multi-energy district boiler and realize significant energy and economic savings. The main drawback of the proposed sequential management strategy lies in not taking into account the future power demand. That is why a strategy based on a Model Predictive Controller (MPC) is likely to improve operation and performance. In order to implement such a controller, the power demand has to be accurately forecasted. As a consequence, a short-term forecast method, based on wavelet-based Multi-Resolution Analysis (MRA) and multilayer Artificial Neural Networks (ANN) is proposed. Both the sequential and the predictive strategies are applied to a northeast France multi-energy district boiler selected as a case study. The main result to retain is that the efficiency of water thermal storage tank is mainly related to its design and the way it is managed. For this case study, the predictive strategy regardless the size of the storage tank, the predictive strategy is more reliable. Furthermore, in all cases an adequately sized and managed thermal storage tank is a profitable investment. It allows the fossil energy consumption to be significantly reduced. The same remark applies to the functioning costs and CO2 emissions

Cities and districts contribute to a large fraction of the total energy consumption in Sweden. The residential- and service sector accounted for almost 40% of the total energy consumption in 2018. The increasing urbanization also puts more importance on the energy supply, distribution and consumption in these areas. One way of planning an energy system in urban areas is to have integrated energy systems where synergies between different technologies and energy carriers are utilized. Such a solution can increase the flexibility of the energy system and thus help integrate more intermittent renewable energy sources. The aim of this study was to suggest tools for planning energy systems in districts. This was done by performing a literature review regarding the design of energy systems and the identification of barriers and opportunities for the integration of different production- and distribution technologies. The focus was on systems for heating, cooling and electricity. The proposed tools are three Excel-based modules. The first module is a qualitative model that presents the reviewed technologies and their connections. It also includes synergies between different energy carriers and sectors for consumption and production. The second module is qualitative model related to market mechanisms, juridical, organizational and institutional aspects. The third module is a table containing the barriers and opportunities. Furthermore, relevant stakeholders are identified to be district heating companies, building owners, joint associations, municipalities, district cooling companies and photovoltaic plant owners. The proposed tools can be used in the first stage of planning when the technologies are selected. To show how the suggested tools can be applied, a case study was performed. The study case is a district being planned in Stockholm, Sweden. For the analysis, a model for a hypothetical heating system was required. Two models were developed for the heat supply system using the modelling environment OpenModelica. The main objective of the case study was to compare the techno-economic and environmental performance of different scenarios. Three different scenarios were considered for covering the total heating demand in the district. In the first scenario the total heating demand is covered only by local heat pumps. In the second scenario the space heating demand is covered by heat pump(s) coupled with a thermal energy storage (hot water tank). An electric boiler is used as backup. In the third scenario, the electric boiler is replaced by district heating as backup. A sensitivity analysis was included for different numbers of heat pumps and different sizes of thermal energy storage in the two last scenarios. The economic and environmental results in this study were strongly dependent on the assumptions regarding prices and emission factors. The result of the case study indicates that the third scenario causes the lowest CO2 emissions. An increased size of the thermal energy storage causes a higher compressor electricity consumption thus more emissions. However the total emissions from the system depends on the backup component. For this result, the emission factor related to Swedish electricity mix and the emission factor stated by a district heating company in Stockholm was used. The cheapest alternative in terms of annual operational cost of energy is the first scenario with only heat pumps. However, from the scenarios which also includes thermal energy storage, the second scenario with three heat pumps and a 100 m3 large thermal energy storage, presents the lowest cost. This system design in scenario 2 is only 0.6% more expensive than the first scenario. For the energy prices, the assumption for electricity is based on hourly values from Nordpol and for heat, the values presented in a normal price list from a district heating company is assumed. Regarding the technical performance of the system the result indicates that the contribution from the thermal energy storage as it is modelled in this case study is not significant on anannual basis. However it is observed that a larger thermal energy storage unit covers a higher fraction of the power demand during the hours it is utilized.
Städer och stadsdelar står för en stor del av totala energikonsumtionen i Sverige. Bostads- och servicesektor stod för ungefär 40% av totala energikonsumtionen under 2018. Den ökande urbaniseringen lägger också mer vikt vid energiproduktion, distribution och konsumtionen i dessa områden. Ett alternativ för planering av energisystem i urbana områden är att ha integrerade energisystem där synergier mellan olika teknologier och energibärare kan utnyttjas. Den typen av system skulle kunna öka flexibiliteten i energisystemet och därför förenkla integrering av oförutsägbara förnybara energikällor. Syftet med denna studie var att föreslå verktyg för planering av energisystem i stadsdelar. Detta gjordes genom en litteraturstudie angående utformningen av olika energisystem samt identifiera hinder och möjligheter för att integrera olika produktions- och distributions teknologier. Fokus låg på systemen för värme, kyla och elektricitet. Det föreslagna verktygen är tre Excel baserade moduler. Den första modulen är en qualitative modell som presenterar de studerade teknologier och deras kopplingar. Den innehåller också synergier mellan de olika energibärarna och konsumtions- och produktionssektorn. Den andra modulen är en qualitative modell, men relaterad till marknad mekanismer, juridiska, organisatoriska och institutionella aspekter. Den tredje modulen är en tabell som beskriver hinder och möjligheter för några av teknologierna. Utöver det de relevanta aktörerna identifierades. För värme-, kyla- och elektricitet marknaden är de fjärrvärmeföretagen, fastighetsägare, samfälligheter, kommuner, fjärrkyla företagen, solcells ägare. De föreslagna verktyget kan användas för planering av energisystem i ett första skede när teknologier ska väljas.  En fallstudie genomfördes för att visa hur det föreslagna verktyget kan användas. Fallstudien en stadsdel som planeras i Stockholm, Sverige. För att genomföra en analys behövdes en modell för ett hypotetiskt värmesystem. Två modeller utvecklades för värmesystemet genom att använda modelleringsmiljön OpenModelica. Det huvudsakliga målet med fallstudien var att jämföra den teknoekonomiska- och miljöinriktade prestandan för olika scenarierna. Tre olika scenarier övervägdes för att täcka totala värmebehovet i stadsdelen. I det första scenariot täcks det totala värmebehovet endast av lokala värmepumpar. I andra scenariot täcks värmebehovet för uppvärmning av värmepump(ar) kopplade till en värmelagrings komponent (ackumulatortank). En elpanna användes för reserveffekt. I tredje scenariot är elpannan ersatt av fjärrvärme. En känslighetsanalys var utförd för olika antal värmepumpar kopplade till olika storlekar av värmelagrings-komponenten i de två sista scenarierna. De ekonomiska och miljörelaterade resultatet i den här studien är starkt beroende av antaganden gällande priser och utsläppsfaktorer. Resultatet indikerar att det tredje scenariot har de lägsta CO2 utsläppen. Ökad värmelagringsstorlek bidrar till att värmepumpen förbrukar mer elektricitet och därför ökar de relaterade utsläppen. Däremot beror de totala utsläppen i systemet på vilken reservkraft som används. För dessa resultat användes utsläppsfaktorn för svensk elmix samt utsläppsfaktorn från ett fjärrvärme företag i Stockholm. Den billigaste alternativet gällande årlig driftsenergikostnad är det första scenariot med endast värmepumpar. Däremot, bland de scenarion som innehåller värmelagring, har det andra scenariot med tre värmepumpar och 100m3 stor värmelagringsenhet den lägsta kostnaden. Detta system är endast 0.6% dyrare än det första scenariot. För energipriser har timvärden från Nordpol antagits för elektricitet och för värme har normalprislistan från ett fjärrvärmebolag i Stockholm antagits. Angående den tekniska systemprestandan, indikerar resultatet att bidraget från värmelagringsenheten som den är modellerad i den här fallstudien inte är signifikant på årsbasis. Det observeras emellertid att en större värmelagringsenhet täcker en större andel av effektbehovet under de timmar som enheten används.

As the world's power needs grow, the demand for power from renewable resources, such as wind or solar is increasing. One major drawback associated with these renewable resources is that the power output is dependent on environmental factors, such as cloud cover and wind speeds. This allows the possibility of either power output exceeding or falling short of forecast levels that may lead to grid instabilities. Therefore, Large Scale Energy Storage (LSES) systems are critical to store excess power when the output exceeds demand in order to supplement output power when it falls short of demand.¹ The Zinc/Bromine Redox Flow Battery (RFB) is a promising technology because of previously reported long cycle-life (CL) capability, high efficiencies, low cost materials, and scalable operating conditions.² The excellent energy storage performance of the Zinc/Bromine system was confirmed by measuring both Faradaic and Coulombic electrochemical cell efficiency dependence on temperature of a bench scale Zinc/Bromine flow cell. At room temperature, near 75% Faradaic efficiency was measured when cycling the system between 20% and 100% State of Charge (SOC), which is in good agreement with published values,³ and was measured to be over 80% efficient when operating at an elevated temperature of 50°C. To elucidate capital and operational costs, key system operation parameters especially focused on degradation mechanisms were investigated. Since deep discharge cycling is perceived as highly damaging to electrochemical systems, a system was cycled between 0% and 5% (SOC) 10,000 times. Performance was quantified by measuring the frequency factor (i[subscript 0]) and relative activation energy (α) for the reactions using Tafel scans. No statistically significant degradation or change to the electrodes was observed during the zero point cycling experiment. However, it was found that under conventional operation damage to the electrodes does accumulate, presumably due to the highly oxidative environment caused by the presence of high concentrations of dissolved bromine or tri-bromide. While the performance of both electrodes shows decreases in frequency factor attributed to the damage process, the bromide oxidation process seems to be more damaging (i.e., at the positive electrode during the charging process). Long term measurements show a degradation of the electrocatalytic parameters at an applied overpotential of 100 mV from ca. 40 mA/cm² to ca. 5 mA/cm² at the positive electrode and from ca. 20 mA/cm² to ca. 10 mA/cm² for the negative electrode. A degradation rate model was proposed to predict the service life expectancy of graphite electrodes in a bromine system based on processes showing a combined second order reaction rate coupled with a negative first order reaction rate. The model can be used to predict the cost of energy when operating any device using graphite electrodes, based on the operating power ratio, defined here as the quotient between operating power and system rated power. This damage could be partially reversed by exposing the electrode surfaces to concentrated potassium hydroxide dissolved in isopropanol, presumably due to exfoliation of the electrocatalytic surface leading to the exposure of a clean surface with electrocatalytic performance close to the original. Further, a chemical pretreatment for the graphite surface imparting enhanced stability in aqueous bromine systems was developed that shows negligible damage when similar amounts of current have passed through the electrode surface. After bromide oxidation equivalent to passing ca. 10 Ah/cm² the treated surface showed a change in steady state current density at an applied overpotential of 100 mV from ca. 50 mA/cm² to ca. 48 mA/cm².
Graduation date: 2013
Access restricted to the OSU Community at author's request from April 1, 2013 - April 1, 2015

Thermal energy storage (TES), the storage of heat or cooling, is a cost-effective energy storage technology that can greatly enhance the performance of the energy systems with which it interacts. TES acts as a buffer between transient supply and demand of energy. In solar thermal systems, TES enables the power output of the plant to be effectively regulated, despite fluctuating solar irradiance. In district energy systems, TES can be used to shift loads, allowing the system to avoid or take advantage of peak energy prices. The benefit of TES, however, can be significantly enhanced by dynamically optimizing the complete energy system. The ability of TES to shift loads gives the system newfound degrees of freedom which can be exploited to yield optimal performance. In the hybrid solar thermal/fossil fuel system explored in this work, the use of TES enables the system to extract nearly 50% more solar energy when the system is optimized. This requires relaxing some constraints, such as fixed temperature and power control, and dynamically optimizing the over a one-day time horizon. In a district cooling system, TES can help equipment to run more efficiently, by shifting cooling loads, not only between chillers, but temporally, allowing the system to take advantage of the most efficient times for running this equipment. This work also highlights the use of TES in a district energy system, where heat, cooling and electrical power are generated from central locations. Shifting the cooling load frees up electrical generation capacity, which is used to sell power to the grid at peak prices. The combination of optimization, TES, and participation in the electricity market yields a 16% cost savings. The problems encountered in this work require modeling a diverse range of systems including the TES, the solar power plant, boilers, gas and steam turbines, heat recovery equipment, chillers, and pumps. These problems also require novel solution methods that are efficient and effective at obtaining workable solutions. A simultaneous solution method is used for optimizing the solar power plant, while a static/dynamic decoupling method is used for the district energy system.
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The objective of this PhD thesis is to create a Unit Commitment and Economic Dispatch (UCED) modelling tool that can used to simulate the deterministic performance of a power system with thermal and renewable generators and energy storage technologies. The model was formulated using mixed integer programing (MIP) on GAMS interface. A robust commercial solver by IBM (CPLEX) is used as solver. Emphasis on the development of the tool has been given on the following aspects. a) Technical impacts of Variable Renewable Energy (VRE) integration. The UCED model developed in this thesis is a high resolution short-term dispatch model. It captures the variability of VRE power on the intra-hour level. In addition the model considers a large number of important real world, system, unit and policy constraints. Detailed representation of a power system allows for a realistic estimation of maximum penetration levels of VRE and the related technical impacts like cycling of generators (part-loading and number of start-ups). b) CO2 emissions. High levels of VRE penetration can potentially increase consumption of fuel in thermal units per unit of electricity produced due to increased thermal cycling. The dispatch of units in the UCED model is based on minimizing system wide operational costs the most important of those being fuel, start-up costs and the cost of carbon. Fuel consumption is calculated using technical data from Input/Output curves of individual generators. The start-up cost is calculated based on times the generator units have been off and the energy requirement to bring the unit back to hot state. Thus dynamic changes on fuel consumption can be captured and reported. c) Technical solutions to facilitate VRE integration. VRE penetration can be facilitated if appropriate solutions are implemented. Energy storage is an effective way to reduce the impact of RE variability. The UCED model includes an integrated Mixed Integer Linear (MILP) compressed air energy storage (CAES) simulation sub-model. Unlike existing CAES models, the new “Thermo-Economic” (TE) CAES model developed in this thesis uses technical data from major CAES manufacturers to model the dynamic effect of cavern pressure on both the compression and expansion sides during CAES operation. More specifically the TE model takes into account that a) a compressor discharges at a pressure equal to the back-pressure developed in the cavern at each moment, b) the speed of charging can be regulated through inlet guide vanes; higher charging speed can take place at the expense of additional power consumption, c) the maximum power output during expansion can be limited by the levels of cavern pressure; there is a threshold pressure level below which the maximum output decreases linearly with pressure. Since it uses actual power curves to simulate CAES operation, the TE model can be assumed to be more accurate than conventional Fixed Parameter (FP) models that don’t model dynamic effects of cavern pressure on CAES operation. The TE model in this thesis is compared with conventional FP models using historical market prices from the Irish electricity market. The comparison was based on the ability of a CAES unit to arbitrage energy for making profit in the Irish electricity market. More specifically a “Base” scenario was created that included the operation of a 270MW CAES unit with technical characteristics obtained from a major CAES manufacturer and assumed discharge time of 13hr. Various sensitivities on discharge time, natural gas prices and system marginal prices (SMPs) were modeled. An additional scenario was created to show the benefit on CAES profitability if the unit participated in both the energy and ancillary services markets. All scenarios were modeled using both the TE and FP CAES models. The results showed that the most realistic TE model returns around 15% less profitability across more scenarios. The reduction in profitability grows to around 30% when the cavern volume (discharge time) is reduced to half (6 hours). The latter is related to the sensitivity of the TE model on cavern pressure that is being built faster when the volume is reduced. A CAES unit won’t get a positive net present value (NPV) in Ireland under any scenario unless SMPs are greatly increased. Thus, it was shown that that existing FP CAES models overestimate CAES profitability. More accurate models need to be used to estimate CAES profitability in deregulated markets. Additionally, it might deem necessary to create additional markets for energy storage units and increase the possible revenue sources and magnitude to facilitate an increase of storage capacity worldwide. The second step of analysis involved the integration of the CAES and UCED models. The UCED model developed in this thesis was validated and applied using data from the Irish grid, a power system with more than 50 thermal generators. A vast of existent data was used to create a mathematical model of the Irish system. Such data include technical specifications and variables of thermal generators, maintenance schedules and historical solar, wind and demand data. The validation exercise was deemed successful since the UCED model simulated utilization factors of 45 out of 52 generators with an absolute difference between modeled and actual results on utilization factors of less than 6% (the absolute differences are called Delta in this thesis). In addition the results of validation exercise were compared with the results of a similar exercise where PLEXOS was the modelling tool and it was found that the results of the two models were similar for the vast majority of generators. More specifically, the PLEXOS model results showed higher deltas for the coal-fired generators compared to the UCED model. On the other hand the UCED model, reported higher delta values for peat-fired generators. The results of the PLEXOS model were slightly better for the gas-fired generators while both models reported deltas nearly zero for all oil and distillate-fired generators. Finally the model was applied to study the benefits of energy storage in Ireland in 2020 when wind penetration is expected to reach 37% of total demand. The analysis involved the development of two groups of 3 scenarios each. In the first group the main scenario also called the “Reference” was used to simulate the short-term unit (30 min step) commitment within the Irish system without storage. The results of the reference scenario were compared with two additional scenarios that assumed the existence of one 270MW CAES unit in Northern Ireland by 2020 (again the first scenario involved the TE and the second the FP CAES model). The results showed –when using the TE model- that the inclusion of one 270MW CAES unit in AI can help reduce wind curtailment by 88GWh, CO2 emissions by 150,000 tonnes and system costs by € 6 million per year. If an FP model had been used instead the reductions would be: wind curtailment by 108GWh, CO2 emissions by 270,000 tonnes and annual system costs by €13 million. Two main conclusions can be obtained from the specific set of results. The first conclusion is that storage units have a financial benefit over the whole system. Thus, when a CAES unit operates to minimize the costs of the whole system can incur substantially more benefits compared to if the CAES unit operated to maximize the individual unit’s profits as in the case presented earlier. The benefits of storage over the whole system should be accounted to make policy decisions and create incentives for investors to increase energy storage capacity in national grids. The second important conclusion is that existing CAES FP models overestimate the ability of a CAES unit to facilitate VRE penetration. More accurate TE models should be used to assess a unit’s capability to increase system flexibility. A second group of scenarios was created to simulate the benefit of CAES at even higher VRE penetration levels. In the second group the “Reference” scenario again, assumed no storage however, wind production was increased by 25%. Again the “Reference” was compared with two additional scenarios that assumed integration of 3x270MW=810MW of storage capacity in AI (one scenario used the TE model and the other the FP). The results for the TE model show that each of the 3 CAES units reduces wind curtailment by 188,000MWh, total system costs by €29 million and CO2 emissions by 180,000 tonnes. The same reductions for the FP model are 217,000MWh of wind curtailment, €25.6 million on total system costs and 180,000 tonnes of CO2. Thus, the results of the second group of scenarios show that as the installed capacity of both CAES and wind increases in Ireland a) the system-wide benefits of CAES increase and b) the differences on results between the TE and FP models become much smaller.

This study centered on a novel thermoelectric generator (TEG) integrated into the built environment. Designed by Watts Thermoelectric LLC, the TEG is essentially a novel assembly of thermoelectric modules whose required temperature differential is supplied by hot and cold streams of water flowing through the TEG. Per its recommended operating conditions, the TEG nominally generates 83 Watts of electrical power. In its default configuration in the built environment, solar-thermal energy serves as the TEG’s hot stream source and geothermal energy serves as its cold stream source. Two systems-level, thermodynamic analyses were performed, which were based on the TEG’s upcoming characterization testing, scheduled to occur later in 2011 in Detroit, Michigan. The first analysis considered the TEG coupled with a solar collector system. A numerical model of the coupled system was constructed in order to estimate the system’s annual energetic performance. It was determined numerically that over the course of a sample year, the solar collector system could deliver 39.73 megawatt-hours (MWh) of thermal energy to the TEG. The TEG converted that thermal energy into a net of 266.5 kilowatt-hours of electricity in that year. The second analysis focused on the TEG itself during operation with the purpose of providing a preliminary thermodynamic characterization of the TEG. Using experimental data, this analysis found the TEG’s operating efficiency to be 1.72%. Next, the annual emissions that would be avoided by implementing the zero-emission TEG were considered. The emission factor of Michigan’s electric grid, RFCM, was calculated to be 0.830 tons of carbon dioxide-equivalent (CO2e) per MWh, and with the TEG’s annual energy output, it was concluded that 0.221 tons CO2e would be avoided each year with the TEG. It is important to note that the TEG can be linearly scaled up by including additional modules. Thus, these benefits can be multiplied through the incorporation of more TEG units. Finally, the levelized cost of electricity (LCOE) of the TEG integrated into the built environment with the solar-thermal hot source and passive ground-based cold source was considered. The LCOE of the system was estimated to be approximately $8,404/MWh, which is substantially greater than current generation technologies. Note that this calculation was based on one particular configuration with a particular and narrow set of assumptions, and is not intended to be a general conclusion about TEG systems overall. It was concluded that while solar-thermal energy systems can sustain the TEG, they are capital-intensive and therefore not economically suitable for the TEG given the assumptions of this analysis. In the end, because of the large costs associated with the solar-thermal system, waste heat recovery is proposed as a potentially more cost-effective provider of the TEG’s hot stream source.
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