Conselho Nacional de Desenvolvimento Científico e Tecnológico / This work reports an experimental investigation related to the drop-in process of HCFC22 in a commercial refrigeration system with a maximum capacity of 15 kW. Among the alternative refrigerants there are hydrocarbons (HCs) and synthetic refrigerants, HFC. The experimental facility is basically composed of analternative variable speed compressor (VSC), tube in tube heat exchangers and an electronic expansion valve (EEV). Different methodologies were addressed to this document. Initially, the systemoperated at the nominal frequency and has been configured to the same openning condition in the expansion valve. The limits of the refrigeration system were operated by factorial experimental designs. Therefore,there were presented response surfaces and metamodels, showing consistent tools to predict the cooling system behavior. Also, an analysis of the individual performance of each refrigerant was held in three different evaporation temperatures: -15ºC, -10ºC and -5ºC. All fluids, except R134a can be suitable to replace R22 in these specific applications. Both HCs and HFC32 provide the refrigeration capacity and COP greater than the original system. In addition, the environmental impact of each fluid was estimated by the TEWI method. HCs showed the lowest impacts, while HFC404A promoted the greatest damage to the environment. Finally, the analysis of the operating system with a Scroll compressor was made. Among the seven options to R22, only five refrigerants operated in stable condition. Moreover, even with handling system parameters, this class of compressors was less flexible to the proposed drop-in. In general, as a great technical contribution for refrigeration systems, this study found that, regardless of the installation capacity, the EEV/VSC pair functionality is an essential tool not only for the adaptation of an alternative fluid to the original compression cycle, as well as to reduce environmental impacts. / O presente trabalho relata uma investigação experimental do processo de drop-in(substituição direta) do HCFC22 em um sistema de refrigeração comercial com capacidade máxima de 15kW. Entre os refrigerantes alternativos testados, encontram-se hidrocarbonetos e refrigerantes sintéticos da classe HFC.A bancada experimental é composta, basicamente, de um compressor de velocidade variável(CVV) alternativo, trocadores de calor de tubos concêntricos e uma válvula de expansão eletrônica (VEE). Inicialmente, o sistema operou à frequência nominal e foiconfigurado à mesma condição de abertura no dispositivo de expansão. Posteriormente, os limites de cada refrigeranteforam explorados por meio de ferramentas estatísticas DOE,design of experiments. Nesta segunda etapa, foram apresentadas superfícies de respostas e metamodelos, que se mostraram ferramentas coerentes na previsão do comportamento do sistema de refrigeração.Em sequência,foirealizada uma análise do desempenho individual de cada refrigerante, em três diferentes temperaturas de evaporação: -15ºC, -10ºC e -5ºC. Todos os refrigerantes, com exceção do R134a, podem substituir o R22 nestas aplicações específicas. Ambos os hidrocarbonetos (HCs) e o HFC32 proporcionaram capacidades de refrigeração e COPs superiores ao sistema original. Em complemento, a estimativa dos impactos ambientais de cada fluidofoi estimada através do método TEWI, total equivalent warming impact. Os HCs apresentaram os menores impactos, enquanto o HFC404A promoveu os maiores danos ao meio ambiente.Por fim, realizou-se a análise do sistema operando com um compressor tipoScroll. Entre as sete opções ao R22, apenas cinco refrigerantes operaram em condições estáveis. Além disso, mesmo com a manipulação de parâmetros do sistema, esta classe de compressores mostrou-se menos flexível à proposta de drop-in.Em geral, como maior contribuição técnica aos sistemas de refrigeração, o presente trabalho comprovou que, independentemente da capacidade da instalação, a funcionalidade do par VEE/CVV é uma ferramenta essencial não só para a adaptação de um fluido alternativo ao ciclo de compressão original, como também para a reduçãodos impactos ambientais. / Doutor em Engenharia Mecânica

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The United Nations recognises anthropocentric greenhouse gas emissions to be the leading cause of global warming. The International Institute of Refrigeration further addresses that in 2014 7.8% of the global greenhouse gas emissions were assigned to the refrigeration sector. This marked the importance of using metrics to evaluate the climate impact of a refrigeration system. However, as these metrics rely on uncertain values it is difficult to assess how reliable they are. The purpose of this study is therefore to evaluate the reliability of two environmental metrics by applying methods for dealing with uncertainties, and to present possible improvements to the applied methods and metric. The study begins by introducing refrigeration systems and their environmentalcontext. In the background the reader is further introduced to the topic by accounting for the evaluated metrics, TEWI and LCCP, as well as three different methods for dealing with uncertainties, Sensitivity analysis, Uncertainty analysis and Monte Carlo Simulation. In order to fulfil the purpose a data centre is modelled, and the restrictions and operation conditions of the system will be further described under section 3. The result will consist of two parts. The first part will consider the theoretical aspect of the study as well as sources and typologies of values and uncertainties. The second part will consist of the empirical results from applying the mentioned methods on the modelled system. These will be presented in graphs sorted after method and metric and are then analysed and evaluated in the discussion. It is seen that only a few parameters dominate the influence in the Sensitivity and Uncertainty analysis but that the influential parameter is dependent on the relative order of magnitude. It is also stated that the LCCP rends no additional information at the analysed conditions. When applying the Monte Carlo Simulation TEWI is considered more reliable, as in that the deterministic value is a more accurate estimation of the ’true’ environmental impact of the system. One possible improvement may be to use the rendered standard deviation for TEWI as an uncertainty range to incorporate the uncertainties in the deterministic value. The study concludes that the Sensitivity and Uncertainty analysis illustrates theinfluence of one single parameter on the final metric value. However, the analyses do not determine to what extent these final values may be considered reliable. A Monte Carlo Simulation is better applicable for some uncertainty typology than others and as such TEWI is considered more reliable than LCCP. The study lands in the conclusion that the presented methods may be improved by assigning uncertainty typologies in order to evaluate the viability of a method to incorporate the uncertainties, e.g. a Monte Carlo Simulation. / Förenta Nationerna erkänner antropocentriska utsläpp av växthusgaser som den främsta orsaken till global uppvärmning. Vidare belyser IIR att kylsektorn stod för 7.8% av de globala utsläppen av växthusgaser år 2014. Detta åskådliggjorde vikten av att använda mätmetoder som kan utvärdera klimatpåverkan hos ett kylsystem. Då dessa mätmetoder baseras på osäkra värden är det svårt att bedöma hur pålitliga de faktiskt är. Syftet med detta projekt är därför att utvärdera tillförlitligheten hos två mätmetoder genom att tillämpa metoder för att hantera osäkerheter och att presentera möjliga förbättringar till de tillämpade metoderna och mätmetoderna. Projektet börjar med att introducera kylsystem och deras miljösammanhang. I bakgrunden får läsaren lära sig mer om ämnet genom en redogörelse för de utvärderade mätmetoderna, TEWI och LCCP, samt tre olika metoder för att hantera osäkerheter, Känslighetsanalys, Osäkerhetsanalys och Monte Carlo-simulation. För att uppfylla syftet modelleras ett data center, och systemets begränsningar och driftsförhållanden beskrivs vidare under rubriken Metod. Resultatet består av två delar. Den första delen redovisar den teoretiska aspekten av studien så som källor för osäkerheter och typologier samt att här tilldelas parametervärden och osäkerheter. Den andra delen består av de empiriska resultaten som fås då metoderna tillämpas på det modellerade systemet. Dessa presenteras i diagram vilka sorteras efter metod och mätmetod. Dessa analyseras och utvärderas sedan i diskussionen. Från resultaten går det att se att endast ett fåtal parametrar dominerar inflytandet i Känslighets- och Osäkerhetsanalysen men att den inflytelserika parametern är beroende av den relativa storleksordningen. Det visar sig även att LCCP inte bidrar till ytterligare information vid de analyserade förhålandena. Vid tillämpningen av Monte Carlo-simuleringen anses TEWI vara mer tillförlitlig. En möjlig förbättring kan vara att använda den givna standardavvikelsen för TEWI som ett osäkerhetsintervall för att inkorporera osäkerheten i det deterministiska värdet. Projektet landar i slutsatsen att Känslighets- och Osäkerhetsanalysen illustrerarinflytandet av en enskild parameter på det slutliga metriska värdet. Analyserna avgör emellertid inte i vilken utsträckning dessa värden kan anses vara tillförlitliga. En Monte Carlo-simulering är bättre tillämplig för en viss osäkerhetstypologi än andra och som sådan anses TEWI vara mer tillförlitlig än LCCP. Projektet landar även i slutsatsen att de presenterade metoderna kan förbättras genom att tilldela osäkerhetstypologier för att utvärdera huruvida en metod kan anses tillämplig för att inkorporera osäkerheter, t.ex. en Monte Carlo-simulering.

Este estudo avalia o desempenho de um sistema em cascata em operação subcrítica utilizando o par R134a/R744, como uma opção a sistemas convencionais em supermercados que normalmente utilizam R404A ou R22. O aparato experimental consiste em um compressor alternativo de velocidade variável para R744 e uma válvula de expansão eletrônica que promove a evaporação direta do CO2 dentro de uma câmara fria (2,3m x 2,6m x 2,5m) para manter a temperatura interna do ar estável. O ciclo de alta temperatura consiste em um compressor alternativo para R134a, uma válvula de expansão eletrônica, e um condensador a ar. Um trocador de calor de placas, que é ao mesmo tempo, o condensador para o R744 e o evaporador para R134a completa a configuração. Durante os testes experimentais, dois parâmetros foram manipulados: o grau de superaquecimento do R744, 515 K, e a frequência de operação do compressor R744, 45-65 Hz. Os valores da capacidade de refrigeração, para R134a/R744 variaram entre 4,30 ± 0,01 e 5,57 ± 0,02 kW, demonstrando a aplicabilidade desse sistema cascata em condições de carga térmica variável. Essa flexibilidade operacional também se estendeu aos valores estabelecidos para a temperatura do ar dentro da câmara fria, sendo o menor valor de -17,7 °C e o mais alto -0,8 °C. A fim de contribuir para a melhoria dos processos de refrigeração, principalmente no que se refere à eficiência energética, foi feito um drop-in no ciclo de alta temperatura, cuja carga de R134a foi substituída por R438A. A comparação foi feita de forma que os sistemas proporcionem capacidades de refrigeração e valores de temperatura do ar dentro da câmara fria semelhantes. Como resultado, o consumo de compressor com R438A foi maior em todos os testes. Os valores de COP para o sistema R134a/R744 variaram de 1,81 ± 0,01 a 2,09 ± 0,01, enquanto no sistema R438A/R744, de 1,41 ± 0,01 a 1,66 ± 0,01. O impacto total equivalente de aquecimento global para o sistema R438A/R744 foi maior em relação ao sistema original, devido ao maior potencial de aquecimento global do fluido R438A e ao maior consumo de potência elétrica do compressor do ciclo de alta temperatura. Logo, o refrigerante proposto no drop-in do sistema de alta temperatura de R134a por R438A provou-se uma alternativa menos eficiente, para as aplicações específicas. / This study evaluates the performance of a cascade system in subcritical operation using the pair R134a/R744, as an option to conventional systems in supermarkets, which usually uses R404A, or R22. The experimental apparatus consists of a variable speed reciprocating compressor for R744 and an electronic expansion valve that promotes direct evaporation of the CO2 inside a cold room (2,3m x 2,6m x 2,5m) to maintain the internal air temperature stable. The high-temperature cycle consists of a reciprocating compressor for R134a, an electronic expansion valve, and an air-cooled condenser. A plate heat exchanger, which is at the same time, the condenser for the R744 and evaporator to R134a completes the setup. During the experimental tests, two parameters were manipulated: The superheating degree of the R744, 5-15 K, and the R744 compressor operation frequency, 45-65 Hz. The cooling capacity values for R134a/R744 ranged between 4,30 ± 0,01 and 5,57 ± 0,02 kW, demonstrating an application to the cascade system under variable thermal load conditions. This operational flexibility also extends to the air temperature values established inside the cold room, being the lower value of -17,7 ° C and higher -0,8 ° C. In order to contribute to the improvement of the cooling processes, mainly about the energy efficiency, a drop-in has been made at the high- temperature cycle, which R134a refrigerant charge has been replaced by R438A. The comparison was done regard both systems providing similar cooling capacities and air temperature values inside the cold room. As a result, the consumption of the compressor operating with R438A was higher in all tests. The COP values for the R134a/R744 system ranged from 1,81 ± 0,01 to 2,09 ± 0,01, while with the R438A/R744 system, from 1,41 ± 0,01 to 1,66 ± 0,01. The total equivalent warming impact for the R438A/R744 system was higher compared to the original system, as a result of the higher GWP for the R438A and higher electrical power consumptions. It has been proven the proposed drop-in, at the high temperature cycle from R134a by R438A, is a less efficient choice for such specific applications. / Dissertação (Mestrado)

This thesis investigates a special type of energy system, namely energy use in supermarkets through modelling, simulations and field studies. A user-friendly computer program, CyberMart, which calculates the total energy performance of a supermarket, is presented. The modelling method described in this thesis has four phases: the first phase is the de-velopment of a conceptual model that includes its objectives, the envi-ronment and the components of the system, and their interconnections. The second phase is a quantitative model in which the ideas from the conceptual model are transformed into mathematical and physical rela-tionships. The third phase is an evaluation of the model with a sensitivity analysis of its predictions and comparisons between the computer model and results from field measurements. The fourth phase is the model ap-plication in which the computer model answers questions identified in the beginning of the modelling process as well as other questions arising throughout the work. Field measurements in seven different supermarkets in Sweden were car-ried out to: (i) investigate the most important parameters that influence energy performance in supermarkets, (ii) analyse the operation of new system designs with indirect system implementation in Sweden during recent years, and (iii) validate the computer model. A thorough sensitivity analysis shows a total sensitivity of 5.6 %, which is a satisfactory result given a 10% change in the majority of input parame-ters and assumptions, with the exception of outdoor temperatures and solar radiation that were calculated as extreme values in METEO-NORM. Comparisons between measurements and simulations in five supermarkets also show a good agreement. Measurements and simula-tion results for a whole year were not possible due to lack of data. CyberMart opens up perspectives for designers and engineers in the field by providing innovative opportunities for assessment and testing of new energy efficient measures but also for evaluation of different already-installed system designs and components. The implementation of new energy-saving technologies in supermarkets requires an extensive inte-grated analysis of the energy performances of the refrigeration system, HVAC system, lighting, equipment, and the total energy usage. This analysis should be done over a long period, to evaluate and compare the real energy performance with the theoretical values calculated by Cyber-Mart. / QC 20100330