The optimizations of air-condition systems using naturalrefrigerants R-600a are studied in this thesis. The theories including the exergy analysis, heat transfer and fluid mechanics are combined together to study the exergy transfer and destroy in each component. The optimizing parameters in this research include cooling air velocities, the tube diameters of evaporator and condenser. If all the conditions remain constant expect the tube diameter of evaporator, the numerical results display that the values of the total entropy generation rate with R-600a decrease from tube diameter 1.0 cm to 1.1 cm and increase from 1.1 cm to 1.2 cm. The tube diameter of evaporator and condenser at a minimum value of total entropy generation rate is 1.1cm for the simulation conditions. Besides, the coefficient of performance and the energy efficiency ratios also have maximum values at the tube diameter. If all the conditions remain constant expect the tube diameters of condenser, the tendencies of total entropy generation rate arethe same as those in evaporator.

The characteristics of thermofluid flow cycle for natural refrigerants R-600a and R-290 applying to an air-conditioning system are studied in this project. In system performance analysis, The exergy analysis incorperated with heat transfer and fluid mechanics are also adopted to analyze the exergy transfer and destroy of each component and the whole system. The simulation parameters in this research include room temperatures, outdoor temperatures, and the types of refrigerants. If all the conditions remain constant except room temperature, the numerical results show that the coefficient of performance (COP) and the energy efficiency ratio (EER) will increase when the room temperature increases, or the outdoor temperature decreases. If all simulation conditions are the same, COP and EER with R-600a is better than those with R-290. By using exergy analysis, the numerical results show that the flow exergies through compressor and expansion valve will decrease due to the friction of the fluid flow. However, the flow exergies through condenser and evaporator will decrease due to finite-temperature heat transfer and energy carried away by exterior air. The destruction of the flow exergy due to the irreversibility of the frictional fluid flow is relative small to heat transfer. By using the exergy analysis, we can clearly understand the exergy change within each component of an air-conditioning system. This treatment is very useful in the design of air-conditioning systems and its optimum analysis.

Heat pumps have been identified as an efficient alternative to traditional boilers for the production of sanitary hot water (SHW). The high water temperature lift (usually from 10ºC to 60ºC) involved in this application has conditioned the type of used solutions. On the one hand, transcritical cycles have been considered as one of the most suitable solutions to overcome the high water temperature lift. Nevertheless, the performance of the transcritical CO2 heat pump is quite dependent on the water inlet temperature, which in many cases is above 10ºC. Furthermore, performance highly depends on the rejection pressure, which needs to be controlled to work at the optimum point in any condition. On the other hand, for the subcritical systems, subcooling seems to be critical for the heat pump performance when working at high temperature lifts, but there is not any published work that optimizes subcooling in the SHW application for these systems. Therefore, the subcritical cycle should require a systematic study on the subcooling that optimizes COP depending on the external conditions, in the same way as it has been done for the rejection pressure in the transcritical cycle. The aim of this thesis is to investigate the role of subcooling in the performance of a Propane water-to-water heat pump for SHW production, in the application of heat recovery from any water source. Two different approaches to overcome the high degree of subcooling were designed and built to test them in the laboratory: 1) Subcooling is made at the condenser: The active refrigerant charge of the system is controlled by a throttling valve. Subcooling is controlled independently at any external condition. 2) Subcooling is made in a separate heat exchanger, the subcooler. Subcooling is not controlled, it depends on the external condition and the heat transfer at the subcooler. The heat pumps were tested at different water temperatures at the evaporator inlet (10ºC to 35ºC) and condenser inlet (10ºC to 55ºC), while the water production temperature was usually fixed to 60¿C. The obtained results have shown that COP depends strongly on subcooling. In the nominal condition (20¿C/15¿C for the inlet/outlet water temperature at the evaporator and 10ºC/60ºC for the inlet/outlet water temperature in the heat sink), the optimum subcooling was about 43 K with a heating COP of 5.61, which is about 31% higher than the same cycle working without subcooling. Furthermore, the system with subcooling has been proved experimentally as being capable of producing water up to 90¿C and has shown a higher COP than some CO2 commercial products (catalog data reference). / Las bombas de calor han sido identificadas como una alternativa eficaz a las calderas tradicionales para la producción de agua caliente sanitaria (ACS). El elevado salto de temperatura del agua que normalmente tiene lugar en esta aplicación (por lo general de 10ºC a 60ºC) ha condicionado el tipo de soluciones que se utilizan. Por un lado, los ciclos transcríticos han sido considerados como una de las mejores soluciones para trabajar con los elevados saltos de temperatura del agua. Sin embargo, el rendimiento de la bomba de calor transcrítica con CO2 es bastante dependiente de la temperatura de entrada del agua, que en muchos casos está por encima de los 10¿C. Además, el rendimiento depende en gran medida de la presión de descarga, la cual necesita ser controlada con el fin de trabajar en el punto óptimo en cualquier condición externa. Por otra parte, para los sistemas subcríticos, el subenfriamiento parece ser crítico para el buen funcionamiento de la bomba de calor cuando se trabaja con elevados saltos de temperatura del agua, pero no hay ningún trabajo publicado en el que optimicen el subenfriamiento para la aplicación de ACS en estos sistemas. Por lo tanto, los sistemas subcríticos requieren de un estudio sistemático para buscar el subcooling óptimo y maximizar el COP en función de las condiciones externas, de la misma forma que se ha hecho para la presión de descarga en los ciclos transcríticos. El objetivo de esta tesis es investigar el papel del subenfriamiento en el rendimiento de una bomba de calor trabajando con Propano para la producción de ACS, en la aplicación de recuperación de calor de cualquier fuente de agua (agua- agua). Dos enfoques diferentes para superar el alto grado de subenfriamiento fueron diseñados y construidos para ponerlos a prueba en el laboratorio: 1) El subenfriamiento se hace en el condensador: La carga activa de refrigerante del sistema se controla con una válvula de estrangulación. De esta manera, el subenfriamiento puede ser controlado de forma independiente a cualquier condición externa. 2) El subenfriamiento se hace en un intercambiador de calor separado, el subenfriadador. El subenfriamiento no se controla, este depende de la condición externa y de la transferencia de calor en el subenfriadador. Las bombas de calor se ensayaron a diferentes temperaturas del agua a la entrada del evaporador (10ºC a 35ºC) y entrada del condensador (10ºC a 55ºC), mientras que la temperatura de producción de agua, normalmente, se fija a 60¿C. Los resultados obtenidos han demostrado que el COP depende mucho del subenfriamiento. En las condiciones nominales (20ºC/15ºC para la temperatura del agua de entrada/salida en el evaporador y 10ºC/60ºC para la temperatura del agua de entrada/salida en el condensador), el subenfriamiento óptimo fue aproximadamente de 43 K con un COP de calentamiento de 5,61, que es alrededor del 31% más alto que el mismo ciclo trabajando sin subenfriamiento. Además, el sistema con subenfriamiento ha probado de forma experimental, que es capaz de producir agua hasta los 90ºC, y ha mostrado un COP más alto que algunos productos comerciales que trabajan con CO2 (datos de referencia del catálogo). / Les bombes de calor han estat identificades com una alternativa eficaç a les calderes tradicionals per a la producció d'aigua calenta sanitària (ACS). L'elevat salt de temperatura de l'aigua que normalment té lloc en aquesta aplicació (en general de 10ºC a 60ºC) ha condicionat el tipus de solucions que s'utilitzen. Per una banda, els cicles transcrítics s'han considerat com una de les millors solucions per tal de treballar amb els elevats salts de temperatura de l'aigua. No obstant això, el rendiment de la bomba de calor transcrítica amb CO2 és bastant dependent de la temperatura d'entrada de l'aigua, que en molts casos està per damunt de 10¿C. A més, el rendiment depèn en gran mesura de la pressió de descarrega, la qual necessita ser controlada per tal de treballar en el punt òptim a qualsevol condició externa. Per altra banda, per als sistemes subcrítics, el sub-refredament sembla ser crític per al funcionament de la bomba de calor quan es treballa amb elevats salts de temperatura de l'aigua, però no hi ha cap treball publicat en el qual optimitzen el sub-refredament per a l'aplicació d'ACS en aquests sistemes. Per tant, els sistemes subcrítics requereixen d'un estudi sistemàtic per tal de buscar el subcooling òptim i maximitzar el COP en funció de les condicions externes, en la mateixa forma que s'ha fet per la pressió de descarrega en els cicles transcrítics. L'objectiu d'aquesta tesi és investigar el paper del sub-refredament en el rendiment d'una bomba de calor treballant amb Propà per a la producció d'ACS, en l'aplicació de recuperació de calor de qualsevol font d'aigua (aigua-aigua). Dos enfocaments diferents per tal de superar l'alt grau de sub-refredament van ser dissenyats i construïts per posar-los a prova en el laboratori: 1) El sub-refredament es fa en el condensador: La càrrega activa de refrigerant del sistema es controla amb una vàlvula d'estrangulació. D'aquesta manera, el sub-refredament pot ser controlat de forma independent en qualsevol condició externa. 2) El sub-refredament es fa en un intercanviador de calor separat, el sub-refredador. El sub-refredament no es controla, este depèn de la condició externa i de la transferència de calor al sub-refredador. Les bombes de calor es van assajar a diferents temperatures de l'aigua a l'entrada de l'evaporador (10ºC a 35ºC) i a l'entrada del condensador (10ºC a 55ºC), mentre que la temperatura de producció d'aigua, normalment, es fixa a 60¿C. Els resultats obtinguts han demostrat que el COP depèn molt del sub-refredament. En les condicions nominals (20ºC/15ºC per a la temperatura de l'aigua d'entrada/eixida a l'evaporador i 10ºC/60ºC per a la temperatura de l'aigua d'entrada/eixida en el condensador), el sub-refredament òptim és aproximadament de 43 K amb un COP d'escalfament de 5,61, que és al voltant del 31% més alt que el mateix cicle treballant sense sub-refredament. A més, el sistema amb sub-refredament ha provat de forma experimental, que és capaç de produir aigua fins als 90ºC, i ha mostrat un COP més alt que alguns productes comercials que treballen amb CO2 (dades de referència del catàleg). / Pitarch I Mocholí, M. (2017). High capacity heat pump development for sanitary hot water production [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/81858

Made available in DSpace on 2014-12-17T14:58:05Z (GMT). No. of bitstreams: 1 IgorMGA_DISSERT_1-100.pdf: 3498388 bytes, checksum: 478be24ae351a921f1a23bafc58492ef (MD5) Previous issue date: 2010-12-20 / This research this based on the seminar on Use of Natural Fluids in Refrigeration and Air-Conditioning Systems conducted in 2007 in Sao Paulo. The event was inserted in the National Plan for Elimination of CFCs, coordinated by the Ministry of Environment and implemented by the United Nations Development Programme (UNDP). The objective of this research is analyze the performance of the hydrocarbons application as zeotropic mixtures in domestic refrigerator and validate the application of technical standards for pull down and cycling (on-off) tests to the mixture R290/R600a (50:50) in domestic refrigerator. It was first developed an computational analysis of R290/R600a (50:50) compared to R134a and other mass fractions of the hydrocarbons mixtures in the standard ASHRAE refrigeration cycle in order to compare the operational characteristics and thermodynamic properties of fluids based on the software REFPROP 6.0. The characteristics of the Lorenz cycle is presented as an application directed to zeotropic mixtures. Standardized pull down and cycling (on-off) tests were conducted to evaluate the performance of the hydrocarbons mixture R290/R600a (50:50) as a drop-in alternative to R134a in domestic refrigerator of 219 L. The results showed that the use of R290/R600a (50:50) with a charge of refrigerant reduced at 53% compared to R134a presents reduced energy performance than R134a. The COP obtained with hydrocarbon mixture was about 13% lower compared to R134a. Pull down times in the refrigerator compartments for fluids analyzed were quite close, having been found a 4,7% reduction in pull down time for the R290/R600a compared to R134a, in the freezer compartment. The data indicated a higher consumption of electric current from the refrigerator when operating with the R290/R600a. The values were higher than about 3% compared to R134a. The charge of 40 g of R290/R600a proved very low for the equipment analyzed / Esta pesquisa est? baseada no semin?rio Uso de Fluidos Naturais em Sistemas de Refrigera??o e Ar-Condicionado realizado em 2007 na cidade de S?o Paulo. O evento esteve inserido no Plano Nacional de Elimina??o de CFC?s, coordenado pelo Minist?rio do Meio Ambiente e implementado pelo Programa das Na??es Unidas para o Desenvolvimento (PNUD). O objetivo do trabalho ? analisar a performance da aplica??o de hidrocarbonetos como misturas zeotr?picas em refrigerador dom?stico e validar a aplica??o das normas t?cnicas de ensaios de abaixamento de temperatura e ciclagem para a mistura R290/R600a (50:50) em refrigerador dom?stico. Foi desenvolvida primeiramente uma an?lise computacional do R290/R600a (50:50) em rela??o ao R134a e outras fra??es de massa da mistura de hidrocarbonetos operando no ciclo de refrigera??o padr?o ASHRAE de modo a comparar as caracter?sticas operacionais e termodin?micas destes fluidos com base no software REFPROP 6.0. As caracter?sticas do ciclo Lorenz s?o apresentadas como aplica??o direcionada ?s misturas zeotr?picas. Ensaios normalizados de abaixamento de temperatura e ciclagem foram desenvolvidos para avaliar a performance da mistura de hidrocarbonetos R290/R600a (50:50) como uma alternativa de drop-in do R134a em refrigerador dom?stico de 219 litros de capacidade. Os resultados mostraram que a utiliza??o do R290/R600a (50:50) com uma carga reduzida em 53% da carga de R134a apresenta desempenho energ?tico ligeiramente inferior ao R134a. O COP obtido para a opera??o com a mistura de hidrocarbonetos foi cerca de 13% inferior em rela??o ao R134a. Os tempos de abaixamento de temperatura nos compartimentos do refrigerador para os fluidos analisados foram bastante pr?ximos, tendo sido verificada uma redu??o de 4,7% no tempo de abaixamento para o R290/R600a em compara??o ao R134a, no compartimento do freezer. Foi verificado um maior consumo de corrente el?trica do refrigerador quando operando com o R290/R600a. Os valores obtidos foram superiores cerca de 3% em rela??o ao R134a. A carga de 40 g do R290/R600a se mostrou diminuta para o equipamento analisado

Due to their high global warming potential (GWP), fluorinated refrigerants are being replaced in many heat pump and refrigeration systems. Especially in small systems such as heat pump tumble dryers (HPTD), the replacement of the globally used working fluid in this application, R134a, appears to be manageable. One established alternative is the use of hydrocarbon refrigerants. Within this research project, new zeotropic refrigerant blends of hydrocarbons are theoretically evaluated as retrofit substitutes for R134a in heat pump tumble dryers. The aim is to use the temperature glide inherent to zeotropic mixtures during phase change to increase the heat transfer efficiency and thus, the COP of the system. A mixture of R290 (propane) and RE170 (dimethyl ether) was selected and experimentally investigated in a commercially available HPTD. To assess the new mixture, parameters relevant to the cycle such as pressure, temperature, compressor power, and the dryer moisture extraction rate are compared to those values achieved using the refrigerant R134a. Retaining the heat exchanger and compressor from the R134a system, the system charge with the new mixture was 40 % lower, while the thermal capacity was equal to or higher than that of the R134a system. The increased temperature level supplied by the mixture reduced the drying time and the energy consumption of the HPTD. The investigation showed that the heat exchanger design needed to be adapted to the temperature glide properties of the mixture in order to realize meaningful heat transfer efficiency gains.