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All energy, wind, water, biofuel and fossil fuel besides nuclear- and tide power originates from the sun. It’s very hard to take full advantage of the huge amount of energy hitting the earth each day from the sun. The suns highest radiation appears often when the energy need reaches its lowest. That’s why it’s very important to be able to store energy over time when the sun doesn’t shine. A large part of energy storage is thermal energy storage, which can either be done sensible, latent or chemical. Another possible thermal storage is a combination of sensible and latent. This exam was aiming to investigate different types of energy storage methods available on the market and a much more detailed analysis for different storage methods with phase change materials (PCM). A new method was designed for a new storage tank suitable for Absolicon Solar Collector AB and their energy park in the city of Härnösand. The methods for this exam were to create a theoretical storage tank suitable to Absolicons Energy Park with some simple calculations. The criteria for the storage tank was to create a storage tank that could provide the district heat in Härnösand with 160 degrees pressurized water and create 160 degrees steam to the industry. The dimensions of the storage tank where chosen by the conditions in Härnösand and from the specific data of Härnösands district heat and from Absolicons new solar collectors. The work temperature of the system were set to 160 degrees which meant that the storage tank would be able to work in those conditions with high temperature. A suitable phase change material and methods for encapsulation of the phase change material suitable for this system was to be found. Small tests were made with a new type of encapsulation for phase change materials in higher temperature. Simple calculations of two types of storage tanks were made. The first storage tank was made with a PCM from PCM products named A164. This PCM was encapsulated with special bags that could handle temperature up to 200 degrees with surrounding rapeseed oil and a copper loop that handled the heat transfer. The second thank was made with the same PCM and encapsulation but with water glycol surrounding the PCM and two types of heat exchangers for the heat transfer. The results from the first tank were that it didn’t work with the district heat. Because a wrong calculation with the schematic of the system made it impossible to connect into the district heat of Härnösand. The only good thing was that it didn’t need to be pressurized because of the rapeseed oil but the bad heat transfer between oil and water made a pressurized tank of water more profitable. The results from the second tank showed that it could produce 160 °C to the district heat for 2 h and 7 minutes. The schematic connection worked and the tank would in the near future be able to connect into the district heat. The result for the encapsulation showed that the bags were able to stand temperatures up to 190 degrees for a short period of time.

In this investigation an electric field was applied to a phase change thermal storage system while it was discharging energy. The phase change material used was octadecane. Octadecane is a high purity dielectric material that has a melting temperature close to room temperature. The material was forced to solidify using a heat exchanger mount below the phase change material, cold water flowed through the heat exchanger to ensure it maintained a constant temperature below the melting temperature of the phase change material. By applying -8kV to 9 electrodes – positioned in the phase change material – and by using the heat exchanger as an electrical ground – an electric field was generated in the phase change material. The electric field caused unbalanced body forces in the fluid which generated electro-convection in the fluid. The system was designed such that electro-convection is the only source of convection in the system to isolate the effects of electro-convection, allowing for the underlying physics of electro-convection to be studied easier. To understand the effects of applying electro-convection, a case where there is no applied voltage on the electrodes was compared to a case where there was -8 kV applied to the electrodes. Experiments showed that the effect of applying electro-convection depends on the initial temperature; however, it was found that the improvement after two hours was less than 10%. For a wall temperature of 8.5℃ and an initial temperature of 50℃ - the melting temperate of octadecane is 28℃- then the maximum enhancement of the energy extracted is 50%, but two hours after the start of the test the enhancement approached zero. For a wall temperature of 8.5℃ and an initial temperature of 30℃, the maximum enhancement is 10% and similarly fall to zero after a few hours of application. A simple analytical model was developed. The experimental and numerical results showed that at the early stages of energy discharge the electro-convection case had a large improvement compared to a pure conduction case, however as time progresses this improvement decreases. The explanation for the trend is that adding convection only increases the rate that energy is taken out of the liquid, thus the maximum improvement is bounded by the amount of sensible energy in the liquid phase change material, once this sensible energy is removed applying electrohydrodynamics is no longer beneficial. / Thesis / Master of Applied Science (MASc)

Today's energy production is changing from scheduled to intermittent generation due to the increasing energy injection from renewable sources. This alteration requires flexibility in energy generation and demand. Electric heat pumps and thermal storages were found to have a large potential to provide demand flexibility which is analysed in this work. A three-fold method is set up to generate thermal load profiles, to simulate heat pump pools and to assess heat pump flexibility. The thermal profile generation based on a combination of physical and behavioural models is successfully validated against measurement data. A randomised system sizing procedure was implemented for the simulation of heat pump pools. The parameter randomisation yields correct seasonal performance factors, full load hours and average operation cycles per day compared to 87 monitored systems. The flexibility assessment analysis the electric load deviation of representative heat pump pool in response to 5 different on / off signals. The flexibility is induced by the capacity of thermal storages and analysed by four parameters. Generally, on signals are more powerful than off signals. A generic assessment by the ambient temperature yield that the flexibility is highest for heating days and the activated additional space heating storage: Superheating of the storage to the maximal temperature provides a flexible energy of more than 400 kWh per 100 heat pumps in a temperature range between -10 and +13 °C.

[pt] O presente trabalho versa sobre o estudo e modelagem de um sistema de refrigeração para ar condicionado de edifícios. O modelo considera um sistema de compressão de vapor de grande porte, chamado habitualmente chiller; um tanque de armazenamento de água gelada e uma torre de resfriamento.Para o desenvolvimento do modelo utilizam-se as equações constitutivas e as equações de conservação da massa e energia em todos seus componentes.O modelo permite obter as condições de funcionamento ótimo do sistema de refrigeração reduzindo o tamanho de seus componentes (menor custo de investimento) e o consumo de energia (custo de operação) em correspondência com o diagrama de carga térmica do edifício.Consideram-se as variações da temperatura do meio ambiente ao longo do dia (transiente horário) para estudar a influência destas variações no desempenho global do sistema de refrigeração.Aplica-se o modelo à obtenção das características dos componentes do sistema de refrigeração para condicionamento de ar de um dos blocos do prédio Cardeal Leme da PUC-Rio.No presente estudo, a estratégia de operação usada é um fator decisivo na seleção da melhor alternativa econômica. / [en] The present work aims the study and modeling of a system of refrigeration systems for air-conditioning in buildings. The model considers a high capacity vapor-compression refrigeration system, for water cooling (chiller); a tank of thermal storage tank and a cooling tower.For the development of the model the constitutive equations and the equations of conservation of mass and energy are used over all its components.The model provides the optimal operating conditions of the refrigeration system to reduce the size of its components (lesser cost of investment) and the energy consumption (operation cost) according to the thermal load of the building.Daily temperature variations of the environment are taken into account (hourly transient) in order to study the influence of these variations over the global performance of the refrigeration system.The model is applied to the study of the air conditioning system of one block of the Cardeal Leme building, at PUC-Rio.In the present study, the strategy employed is a keye factor in the selection of the best economical alternative.

Sustainable energy solutions are necessary in developing nations as current food preparation practices are becoming harmful to the environment, economic development and the overall health of the population. The purpose of this study was to create a Scheffler reflector-based system prototype, experimentally analyze the system and to predict its behavior when subjected to the solar conditions of Rajasthan, India. Former designs from India, the University of Iowa and several other institutions were consulted during the formulation of the prototype design. While consulting a specific set of design constraints, pertinent to developing counties, a Scheffler reflector and tracking stand were fabricated. Solutions for a thermal storage unit were investigated for eventual integration with the prototype. Solar flux data for Iowa and India was used to predict the amount of energy transmitted by the reflector. Experiments were designed and completed to observe the temperatures experienced at the focal point of the reflector and estimate the energy stored by a steel mass. A series of sun angles, monthly solar flux data and experimental data were used to predict the performance of the storage unit, over a three day span, in Rajasthan. Aspects of the system were then modified to investigate their effects on the temperature of the storage unit.

A thermal energy store corrects the misalignment of heating demand in the winter relative to solar thermal energy gathered in the summer. This thesis reviews the viability of a solar charged hot water tank thermal energy store for a school at latitude 56.25N, longitude -120.85W

The world faces two major energy-related challenges: reducing greenhouse-gas emissions and improving energy security. Wind-electricity, a clean and environmentally sustainable energy source, appears promising. However, its intermittency is problematic when used as a supply for on-demand electricity. Wind-electricity can be used for space heating when combined with thermal-storage systems; although its intermittency can result in periods of excess electricity. To reduce the excess, this thesis proposes using wind-electricity for thermal-storage and electric-vehicles. Four charging procedures are designed and developed. Data from an eastern Canadian wind-farm is used to demonstrate the procedures. The results are compared and discussed in terms of the supply of wind-electricity and its ability to meet the energy requirements of these services. Depending on the procedure, wind-electricity displaced between 20 and 26 GWh of energy previously required for space-heating and transportation, demonstrating that wind-electricity, with intermittently-chargeable loads using storage, is a solution to the intermittency problem.

A novel multi-tank thermal energy storage (TES) was evaluated experimentally and numerically. The multi-tank storage is based on the interconnection of standard hot water storage tanks by a single charge flow loop. Each tank is charged through a thermosyphon loop and natural convection heat exchanger (NCHE). Both series- and parallel-connected configurations were investigated and results show that high degrees of stratification can occur. To predict the performance of the series- and parallel-connected multi-tank TES, a numerical model was developed and implemented in the TRNSYS simulation environment. Laboratory tests were also conducted to measure the unit’s performance under charge conditions representative of combinations of clear and overcast days. The effects of rising and falling charge loop temperatures and power levels on storage temperatures and heat transfer rates were studied and indicated that sequential stratification was achieved in the series-connected storage. Under certain conditions, reverse flow through the thermosyphon loops was identified, leading to destratification and carry-over of heat to the downstream storage tanks. Consequently, a new model was developed and showed to model reverse thermosyphon operation. A subsequent analysis showed that these effects could be minimized by careful system design. To quantify the relative benefits of the sequentially stratified TES, values of exergy stored versus time were determined and compared against fully stratified and fully mixed storages. Results show that the series configuration closely matches the exergy level attained by a perfectly stratified storage. Finally, annual simulations conducted for a typical multi-family installation showed that the multi-tank storage performed at a level comparable to a single, fully stratified, storage. / Thesis (Ph.D, Mechanical and Materials Engineering) -- Queen's University, 2009-06-24 00:13:01.142

Made available in DSpace on 2014-06-11T19:25:27Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-06-27Bitstream added on 2014-06-13T19:32:34Z : No. of bitstreams: 1 souza_lmp_me_bauru.pdf: 1572366 bytes, checksum: b4f3b5bc0ddb17fad3e39f5f59ec6a72 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / No estudo de reaproveitamento de energia térmica, os refrigeradores domésticos dissipam calor para o meio ambiente, através do seu condensador, e esse calor pode ser reciclado, ou seja, recuperado através de escoamento de água, como fluido refrigerante escoando pelo condensador e armazenada em um reservatório. Para isto, construi-se um aparato experimental contendo um refrigerador doméstico, duplex com capacidade de 263 litros para o gabinete de refrigeração e 74 litros para o gabinete de congelamento. O refrigerador tem seu condensador acrescido por um trocador de calor tipo tubos concêntricos em contra corrente, cuja fruição é condensar o fluido refrigente utilizando água em circulação. Dessa forma, caso ocorra o carregamento térmico total do tanque de armazenagem, o calor será originalmente dissipado para o meio ambiente, através do condensador aletado. A água aquecida é então armazenada em um reservatório térmico via estratificação térmica. Assim calculou-se as vazões de água aquecida e fluido refrigerante, como também o coeficiente de desempenho do sistema acumulado. Os resultados mostraram que a vazão de água bem como o coeficiente de desempenho do sistema aumenta de acordo com o aumento da pressão hidrostática. Desta maneira, dos resultados obtidos pode-se concluir que a otimização do experimento se dá de forma eficaz e que, o reaproveitamento da água quente proveniente do condensador é perfeitamente possível, reduzindoo consumo de energia elétrica com aquecedores de água e ainda, minimizando a dissipação de calor para o meio ambiente, sem alterar o funcionamento do refrigerador / In the study of recycling thermal energy it is know that domestic refrigerators dissipate heat to environment through the condenser. This heat can be recycled by a water flow, as a coolant in a modified condenser, and stored in a Domestic Hot Water Storage Tanks (DHWST). Thereby, an experimental apparatus was built containing one domestic refrigerator, each one with capacity of 263 liters in the cooling cabinet and 74 liters in the freezing cabinet. The refrigerators had the condenser increase by a type heat exchanger concentric tubes with a counter-current flow, which has the function of replace the original finned exchanger, condensing the coolant with water flow. Thus, in case the total thermal loading of the storage tank, the heat is dissipated to the original environment through the condenser finned. The heated water is then stored in a thermal reservoir via thermal stratification. In these conditions, the flow of heated water and refrigerant was calculated, as well as the coefficient of performance of the system. The results show that the water flow rate and the coefficient of performance of the system increases with the increase in hydrostatic pressure. According to these results, the experiment optimization is effective and it is totally possible to reuse the warm from modified condenser system, what could reduce the electric energy consumption in water beater and minimize the heat dissipation to environment, without modifying the refrigerator operation