A detailed analysis of the heat transfers and fluid flows within a direct thermosyphonic solar-energy water-heater has been undertaken. The collector energy equations when cast in a two-dimensional form enabled heat transfer and thermal capacitance effects to be simulated accurately at the small flow rates encountered commonly in such systems. An investigation of thermocline relaxation processes within the store indicated negligible mixing at the store inlet over a wide range of Richardsons numbers (43,608 < Ri < 729,016). Thermal relaxation under conditions of no flow was shown to be due predominantly to axial conduction along the store wall. The use of an appropriate non-isothermal friction factor correlation when calculating frictional losses in the collector's riser pipes, produced predicted steady-state flow rates which were corroborated experimentally to within 2%. An indoor test facility, monitored and controlled by a microcomputer, enabled 'real' operating conditions to be simulated. The predicted responses of the system to identical conditions showed good agreement with the corresponding experimental observations, the predicted heat delivery being within 2.8% of the measured value. A technique for correlating the daily performances of thermosyphon solar-energy water-heaters has been developed. The five dimensionless groups which form the basis of the correlations and the functional relationships between these groups were derived from an analytical solution of a linear first-order differential transient heat balance carried out on a generic system. Thermal performance data used in the correlations was generated by the numerical simulation using representative U. K. hourly weather data and operating conditions. The minimum amount of data required to establish a characteristic curve for an individual system was found to be thirty days. Using such a curve, the total annual solar fraction agreed with that predicted by the high level model to within 3%. Two universal curves were determined in which the gradients of characteristic curves were correlated against the derived dimensionless groups. The accuracy of the resulting two-stage algorithm in determining annual solar fractions was established as ranging from 5.5% for predominantly multiple-pass systems to a mean of 10.5% for single-pass systems.

Este trabalho propõe um método com objetivo de avaliar a eficiência energética de aquecedores de água residenciais de acumulação elétricos. Os aquecedores foram submetidos a um ciclo de operação simulando uma condição de uso para o cálculo da eficiência. Este ciclo de duração de um dia é composto pelas fases: produção de água quente, reaquecimento e manutenção da temperatura interna. O método foi aplicado no programa experimental e permitiu a identificação de diversos parâmetros referentes ao funcionamento dos aquecedores, tais como: perda passiva por 24 horas, produção de água quente, tempo de reaquecimento, variação da temperatura interna da água e a sua eficiência energética. / This work proposes a method with objective of evaluating the energy efficiency of electrical residential storage water heaters. The heaters were submitted to an operation cycle simulating a use condition for the calculation of the efficiency. This cycle with duration of one day is composed by the phases: hot water withdrawal, temperature recovery and standby thermal loss. The method was applied in the experimental program and it allowed the identification of several parameters regarding the operation of such heaters as: standby thermal loss per 24 hours, hot water rate output, reheating time, cyclic variation of the temperature and its energy efficiency.

Este trabalho propõe um método com objetivo de avaliar a eficiência energética de aquecedores de água residenciais de acumulação elétricos. Os aquecedores foram submetidos a um ciclo de operação simulando uma condição de uso para o cálculo da eficiência. Este ciclo de duração de um dia é composto pelas fases: produção de água quente, reaquecimento e manutenção da temperatura interna. O método foi aplicado no programa experimental e permitiu a identificação de diversos parâmetros referentes ao funcionamento dos aquecedores, tais como: perda passiva por 24 horas, produção de água quente, tempo de reaquecimento, variação da temperatura interna da água e a sua eficiência energética. / This work proposes a method with objective of evaluating the energy efficiency of electrical residential storage water heaters. The heaters were submitted to an operation cycle simulating a use condition for the calculation of the efficiency. This cycle with duration of one day is composed by the phases: hot water withdrawal, temperature recovery and standby thermal loss. The method was applied in the experimental program and it allowed the identification of several parameters regarding the operation of such heaters as: standby thermal loss per 24 hours, hot water rate output, reheating time, cyclic variation of the temperature and its energy efficiency.

In this research, the impact of solar thermal water heaters on the electric water heating load curve in a residential distribution circuit is analyzed with realistic hot water draw profiles. For this purpose, the electric and solar thermal water heater models are developed in MATLAB and validated with results from GridLAB-D and TRNSYS respectively. The solar thermal water heater model is developed for two types of collectors namely the flat plate and evacuated glass tube collector. Simulations are performed with the climate data from two cities - Madison, WI and Tampa, FL - which belong to two very different climate zones in the United States. Minute-by-minute electric energy consumptions in all three configurations of water heaters are modeled for a single water heater as well as a residential distribution circuit with 100 water heaters for daily as well as monthly time frames. The research findings include: The electric energy saving potential of a solar thermal water heater powered by auxiliary electric element is in the range of 40-80% as compared to an all-electric water heater depending on the site conditions such as ambient temperature, sunshine and wind speed. The simulation results indicate that the energy saving potential of a solar thermal water heater is in the range of 40-70% during winter and 60-80% during summer. Solar thermal water heaters aid in reducing the peak demand for electric water heating in a distribution feeder during sunshine hours when ambient temperatures are higher. The simulation results indicate that the peak reduction potential of solar thermal water heaters in a residential distribution feeder is in the range of 25-40% during winter and 40-60% during summer. The evacuated glass tube collectors save an additional 7-10% electric energy compared to the flat plate collectors with one glass pane during winter and around 10-15% during summer. The additional savings result from the capability of glass tube collectors to absorb ground reflected radiation and diffuse as well as direct beam radiation for a wider range of incidence angles. Also, the evacuated glass tube structure helps in reducing wind convective losses. From the simulations performed for Madison, WI and Tampa, FL, it is observed that Tampa, FL experiences more energy savings in winter than Madison, WI, while the energy savings are almost the same in summer. This is due to the fact that Tampa, FL has warmer winters with higher ambient temperatures and longer sunshine hours during the day compared to Madison, WI while the summer temperatures and sunshine hours are almost the same for the two cities. As expected, the simulation results prove the fact that lowering the hot water temperature set point will result in the reduction of electricity consumption. For a temperature reduction from 120 deg. F to 110 deg. F, electric water heaters save about 25-35% electric energy whereas solar thermal water heaters save about 30-40% auxiliary electric energy for the same temperature reduction. For the flat plate collectors, glass panes play an important role in auxiliary electric energy consumption. Flat plate collectors with two glass panes save about 10-15% auxiliary electric energy compared to those with no glass panes and about 3-5% energy saving compared to collectors with one glass pane. This is because there are reduced wind convective losses with glass panes. However, there are also transmittance losses from glass panes and there are upper limits on how many glass panes can be used. Results and findings from this research provide valuable insight into the benefits of solar thermal water heaters in a residential distribution feeder, which include the energy savings and peak demand reduction. / Master of Science

This diploma thesis deals with thermal calculations of fire tube water heater. The first part of the thesis describes different classifications of boilers and water heaters and provides a basic overview for different types of commonly used boilers. The next part describes thermal calculation model created in Maple software, used formulas and algorithm of the model. Subsequently, the model is applied to the experimental water heater in the form of computational rating. In the last part of the thesis the model is applied to the existing operated industrial water heater to evaluate predictive ability of the calculation model by comparing the essential operating parameters obtained from the calculation with real data measured on the water heater.

A steady-state numerical model of a PV/microchannel integrated direct-expansion CO2 heat pump (PV-DXHP) water heater is developed, validated, and analyzed in the present study. To accomplish the objectives, a numerical model of a microchannel evaporator integrated into a CO2 PV DXHP is developed and validated. The effects of evaporator operating parameters on the heat absorption and pressure drop are analyzed. Utilizing the evaporator model, the PV-DXHP model is developed, and the baseline values of the heat pump operating parameters are determined from the evaporator parametric study. The PV-DXHP demonstrates high water heating capability, while maintaining a reasonably high COP. The COP has the highest dependency on the CO2 mass flow rate, while the water outlet temperature has the highest dependency on the water mass flow rate. The results are highly promising and indicate the system has potential to help meet the energy requirements for residential and industrial water heating demands.

This report is concerned with the performance of solar hot water units for laboratory and field use. A solar unit is defined as a system consisting of a collector, storage tank, piping system and controls. Older unites typically employ the thermosyphon principle (gravity) while more recent models use a water pump to circulate the water. Basically, the collector absorbs solar radiation and transfers thermal energy to the water flowing in the collector tubing. From the collector, the fluid is pumped to the storage tank at which point the hot water is available for usage. A literature search revealed that very little information was available concerning test procedures. The National Bureau of Standards (NBS) has generated proposed test procedures for separate testing of the collector and storage tank, but they do not include testing of the total system. The only other suggested test procedure found was by Stotter and Robinson, these authors include a discussion of the total system. Stotter and Robinson along with (NBS) provided the starting point for this report. In the report it is shown that qualitative properties are equally as important as quantitative properties. Quantitative properties are defined as temperature, flowrate, solar radiation or insolation, wind velocity and direction. Qualitative properties are defined as shade, weather resistance, corrosion resistance, location and maintenance. To determine which solar unit properties would be useful in comparing performance values, test reports along with the other references on solar unit testing were studied. After a review of all the reference material the following performance parameters were obtained and are believed to be of use in comparing solar units. These parameters are discussed in detail in the text of the report. 1. nth, the practical thermal efficiency 2. pSTOR, the heat storage coefficient 3. Q, the solar unit capacity 4. Ceff, capacity efficiency. It was found from the error analysis that the recommended instrumentation and test procedure, presented herein, should result in less than ± 10% error in the calculation of performance parameters. Temperature measurement error was found to be the largest contributor to the overall error. It is recommended that the test procedure herein be used for Florida Technological University testing of laboratory and field solar units, and the future work be performed to develop a method of rating solar units.

Le chauffe-eau thermodynamique (CET), dont le principe repose sur une pompe à chaleur (PAC), est l’une des principales solutions pour répondre à l’enjeu de réduction des consommations énergétiques des bâtiments liées à l’eau chaude sanitaire. Le CET le plus courant sur le marché français est composé d’une PAC sur air extérieur, au R134a, dont le condenseur est de type manteau, entourant le ballon de stockage. Bien que le système arrive à maturité, les performances annuelles semblent encore loin des performances théoriques. Cette thèse a donc pour objectif l’optimisation des performances énergétiques des CET, en partant du CET standard français, selon un principe de compromis technico-économique. Pour cela, un modèle détaillé du CET standard est élaboré. La PAC est modélisée sous Dymola à l’aide de la bibliothèque TIL. Le ballon de stockage est modélisé par une combinaison d’une approche zonale et d’un modèle 1D. Ce modèle détaillé est calibré et validé expérimentalement grâce à des essais d’un CET standard réalisé en enceintes climatiques. Ce modèle est ensuite utilisé pour identifier les principaux gisements d’économie d’énergie. Une première analyse permet d’identifier les paramètres les plus influents sur les performances du CET. Cette sélection conduit ensuite à l’élaboration d’un modèle simplifié, plus apte à étudier des périodes longues de fonctionnement en intégrant des critères de coût et de confort. Une étude spécifique, à l’aide d’un algorithme génétique, permet d’évaluer le potentiel d’optimisation lié au pilotage du CET. Une étude multi-paramétrique montre ensuite que le design des échangeurs joue également un rôle important. Les résultats de ces deux voies prometteuses d’optimisation du CET étant inter-dépendants, une dernière partie consiste en une étude multi-critère. Les résultats montrent qu’avec la nouvelle configuration proposée sont obtenus, un meilleur confort thermique sur une plus large gamme de scénario, une augmentation de COP moyenne annuelle de 37 % et une réduction moyenne de facture électrique de 30 %. / Heat Pump Water Heaters (HPWH) are efficient and fast-developing sanitary hot water production systems relying on a heat pump thermodynamic cycle for heat generation, consequently offering a considerable energy saving potential in the buildings sector. The most forthcoming HPWH on the French market are Air-Source Heat Pump Water Heaters (ASHPWH) composed of an exterior air source R134a heat pump and using a wrap-around type condenser, surrounding the thermal storage tank (TST). However, it is found that although these ASHPWH have reached an important level of maturity, it seems that there is still room for improvement of their energy performance. Consequently, the main objective of this PhD thesis is to search for optimization pathways, starting of from the reference ASHPWH on the French market, leading a better technical and economical compromise in terms of ASHPWH design. To reach this objective, a detailed model is first developed using Dymola (Modelica langage). This model comprises of a zonal model and a 1D model for the TST associated to an air source heat pump modeled with the TIL thermal component modeling library. After model calibration, the model is validated thanks to a large set of experimental tests carried out on a standard ASHPWH in climatic cells. The validated model is then used to identify optimization pathways by carrying out annual simulations and identifying energy performance improvement potentials. It is found out that both thermodynamic cycle performance and improved ASHPWH control logics are major contributors to the final energy performance. Both being highly interdependent and impacting energy performances, but also comfort and ASHPWH cost, the last part of the study consists of a multi-criteria optimization. Finally, a new ASHPWH design is proposed achieving better thermal comfort upon a large variety of user draw-off profiles, achieving a 37 % average annual energy saving and a 30 % reduction of the electrical bill.

Este trabalho apresenta uma metodologia de avaliação da incerteza associada à medição do desempenho térmico de coletores solares térmicos, utilizados em aquecedores de água residenciais. A determinação desta grandeza tem influência direta na estimativa da fração solar obtida pelo sistema, e consequentemente no tempo de retorno sobre o investimento do mesmo. Coletores solares planos, construídos a partir de perfis de alumínio, com absorvedores metálicos, pintura preta não seletiva, tubulação interna de cobre, cobertura de vidro simples e isolante térmico na parte traseira, foram ensaiados individualmente em laboratório para determinação do seu desempenho. O procedimento adotado foi o indoor, onde os ensaios são realizados sob um simulador artificial de radiação solar, e envolveu a configuração da câmara de testes, estabilização das variáveis ambientais, ensaios das amostras, cálculo do desempenho térmico e estimativa da sua incerteza associada. Esta última levou em consideração as contribuições da instrumentação empregada, da estabilidade temporal das condições de contorno para realização das medições e do método estatístico utilizado na determinação da curva de desempenho térmico do coletor. Ao final do estudo foram ponderados os limites aceitos pelo programa de etiquetagem brasileiro de coletores em comparação com os resultados obtidos. / This work presents a methodology for assessing the thermal performance uncertainty of solar collectors used in residential water heaters. The uncertainty has a direct influence on the solar fraction prediction and consequently on its payback time. Flat solar collectors, built in aluminum frames, metallic absorber with non-selective black paint, copper pipes, single glass cover and thermal insulation on the back, were tested individually at the laboratory to measure their performance. The test procedure was the indoor, performed on an artificial solar simulator, and included the test chamber set-up, environmental variables control, sample testing, thermal performance calculating and its uncertainty estimate. The latter considered the instrumentation, temporal stability of variables and the statistical method used on the collectors thermal performance curve fitting. The study also compared the results obtained with the performance limits accepted by the Brazilian collector labeling program.

Este trabalho aborda o desenvolvimento de um sistema de controle de temperatura para um aquecedor de passagem de água a gás. O sistema de controle Controlgás é apresentado e comparado ao sistema de controle típico, usado em aquecedores de passagem convencionais. São apresentadas as características e objetivos do projeto Controlgás, o qual serviu de base para o desenvolvimento deste trabalho. É apresentada uma fundamentação teórica sobre técnicas de controle para compensação de variações paramétricas e de atrasos de transporte, bem como uma revisão sobre as principais soluções já desenvolvidas para o controle de temperatura da água em aquecedores de passagem. A bancada experimental, contendo o aquecedor e o sistema de controle, utilizada em trabalhos anteriores, foi reestruturada e instrumentada com sensores de temperatura na entrada e na saída de água e com sensores que detectam a presença de chama e de fluxo de água. Foi desenvolvida uma servo-válvula que permite a regulagem automática da vazão de gás. Desenvolveu-se um circuito de potência para o acionamento dos atuadores (solenoides e servo-válvula) da bancada, assim como algoritmos que geram os sinais adequados para seu funcionamento. Foi feita a identificação do processo e o modelo da servo-válvula foi obtido por meio da análise de ensaios experimentais. O modelo do sistema completo foi desenvolvido no programa Simulink, onde foram feitas simulações do comportamento dinâmico do sistema proposto. O sistema foi implantado experimentalmente e foi capaz de convergir para as temperaturas de referência durante os ensaios. / This work addresses the development of a temperature control system for a gas tankless water heater. The Controlgás control system is presented and compared to typical control systems used in regular tankless water heaters. The characteristics and objectives of Controlgás project, which formed the basis for the development of this work, are presented. A theoretical foundation on control techniques for compensation of parametric variations and transport delays is presented, as well as a review of the main solutions already developed for the control of water temperature on tankless water heaters. The experimental set containing the heater and the control system used in previous work was restructured and instrumented with temperature sensors at the water's input and output and with sensors which detect the presence of flame and the water flow. A servo-valve that allows automatic adjustment of the gas flow was developed. A power circuit was created to drive the actuators (solenoids and servo-valve) of the set, as well as algorithms that generate the appropriate signals for its operation. The process identification and the servo-valve‟s model were obtained through experimental analysis. The system‟s complete model was developed in Simulink, where simulations of the dynamic behavior of the proposed system were made. The system was implemented experimentally and was able to converge to the reference temperatures during the tests.