Merino Coria, Gabriel GuillermoSepúlveda Sepúlveda, Carolina Andrea2016-11-032019-12-182024-05-132024-08-292016-11-032019-12-182024-05-132024-08-292016https://repositorio.udec.cl/handle/11594/2001Tesis presentada para optar el grado de Doctor en Ingeniería Agrícola con mención en Recursos Hídricos en la AgriculturaLa tesis doctoral titulada “Simulación dinámica de un sistema de refrigeración termo solar para la conservación de frutas”, aborda las siguientes temáticas; estado del arte de la refrigeración solar, confección y selección de un año meteorológico típico (TMY) para la ciudad de Chillán, operación y simulación de una cámara frigorífica para la conservación de frutas, modelación de una máquina de refrigeración por absorción con par de trabajo NH3- H2O, y finalmente la simulación dinámica de un sistema de refrigeración solar por absorción para conservación de frutas. El desarrollo de todas estas temáticas permitió demostrar la factibilidad de modelar y simular un sistema de refrigeración termo solar por absorción, con par de trabajo absorbente refrigerante (NH3 - H2O). La modelación y simulación del sistema de refrigeración, permitió evaluar la capacidad de refrigeración, COP, fracciones solares y costos asociados a la refrigeración, para la conservación de frutas en su etapa de post cosecha. El estudio se desarrolló para tres ciudades con diferentes latitudes y condiciones climáticas en Chile, estas fueron Antofagasta, Santiago y Chillán, cuyos niveles de radiación solar las hacen interesantes para la instalación de sistemas termo solares. Antofagasta y Santiago contaban con publicaciones de años meteorológicos tipo (TMY) al comenzar este estudio, que permitían realizar el estudio solar térmico, a diferencia de Chillán, por lo cual se procedió a generar un TMY para Chillán, a partir de la data meteorológica de 15 años con que contaba la Facultad de Ingeniería Agrícola de la Universidad de Concepción. Como resultado, se obtuvo que la conexión serie-paralelo, con colectores FPC es la que genera fracciones solares más altas y menores consumos de calor auxiliar, en las tres ciudades evaluadas. Además, se determinó que Santiago posee el mayor consumo de calor auxiliar por tener un mayor requerimiento de frío, bajo las mismas condiciones de operación de la máquina frigorífica. Esto se debe a las temperaturas extremas que se dan en verano. Sin embargo, si el calor auxiliar fuera suministrado por una caldera de LPG y dado que el coste de este combustible en Santiago es en promedio $70 más bajo por litro, que en las otras dos ciudades, en esta ciudad se tiene el más bajo costo asociado al consumo de calor auxiliar. Así, con un campo de colectores FPC de 80 m2 en la simulación, conectados en serie –paralelo, se tiene en promedio en las tres ciudades una fracción solar de 0,56, con gastos de LPG, iv asociados a la operación desde octubre a marzo de; $3.084.402, $2.807833, y $3.041.813, para Antofagasta, Santiago y Chillán respectivamente. El sistema de refrigeración solar por absorción aumenta el costo de la cadena de valor de la cereza dulce en aproximado de $40 / kg en la temporada, considerando la inversión a 7 años. El hecho de que la máquina esté funcionando durante las 24 horas, provoca un alto consumo de gas, por lo cual se debe buscar una forma de operación que permita conservar la fruta y a su vez limitar la operación de la máquina de absorción a las horas de sol. Esto explica el hecho de el uso de este tipo de refrigeración sea utilizado en su mayor parte para aire acondicionado y no para la conservación de alimentos.The doctoral thesis entitled ‘Dynamic simulation of a solar-powered refrigeration system for the preservation of fruit’, includes the state of the art in solar cooling, the generation and selection of a typical meteorological year (TMY) for the city of Chillán, operation and simulation of a cold room for storing fruits, modeling of an absorption refrigeration equipment for NH3 H2O working pair, and the dynamic simulation of an absorption solar refrigeration system to preserve fruits. Approaching these topics allowed demonstrating the feasibility of modeling and simulating an absorption solar refrigeration system with refrigerant-absorbent working pair (NH3 - H2O). The modeling and simulation of the refrigeration system allowed evaluating the cooling capacity, COP, solar fractions and costs associated with the preservation of fruit during the postharvest stage. This work presents the state of the art of the technologies that are capable of generating cold through solar energy, either through the use of solar collectors or photovoltaic panels, which generate thermal or electrical energy, respectively. For development of the thesis was used a chiller of 12 kW that works with thermal energy (Pink Chiller PCS 12), to produce the temperatures required to preserve fruit. PSC 12 is an absorption chiller of single- effect with refrigerant-absorbent working pair NH3 - H2O. The absorption chiller requires the following equipment for its operation, which is intended to provide heat in the circuit that goes to the generator: solar flat-plate collectors (FPC), evacuated tube collectors (ETC), a sensible heat storage tank and an auxiliary piece of equipment that delivers heat to the system when solar radiation is not enough. These collectors are connected in series, and series-parallel to the heat storage tank. The cooling circuit is the one that generates cold in the cold room and the cooling circuit that links the absorber and condenser of the chiller is connected to a refrigeration tower or can use water of rivers, wells, pool or other water sources. The study was conducted in three cities with different latitudes and climatic conditions in Chile: Antofagasta, Santiago and Chillan. All of them present solar radiation levels that are interesting for the installation of solar thermal systems. Typical meteorological years (TMY) were available for Antofagasta and Santiago and these data allowed performing the solar thermal study. Nevertheless, as TMY data were not available for Chillán, a TMY was generated based on the weather data of 15 years available at the College of Agricultural Engineering at the University of Concepción. Weight factors were used for the meteorological variables, which were presented by five different authors in the generation of a TMY. A hot water system developed in TRNSY was used to evaluate the models. The collector area, hot temperature and volume of the tank varied to determine the TMY in order to represent the 15 years of data. Finally, the TMY which was generated based on the weight factors given by ASRAHE was selected as the most representative for Chillán. The chilling requirement of the fruit to be refrigerated during the postharvest stage (October to March) was estimated. A simulation was developed in TRNSYS considering all chilling requirements and losses in a cold room of 27.5 m3, intended to refrigerate different types of fruit in the 3 cities included in this study. The simulations allowed determining the chilling requirements of the cold room under different operating conditions in terms of volume of fruit, type of fruit, storage temperature and chill hours, among others. This showed that different ways of operating the cold room resulted in different chilling requirements. Therefore, it was concluded that the operation of a cold room needs to be determined before selecting the refrigeration equipment to be used. The absorption chiller was included to the dynamic simulation using experimental data from the Multifunction Laboratory of the Research Group of Applied Thermal Engineering (CREVER) of the Universitat Rovira i Virgili. Based on these data, the simple-effect NH3 - H2O absorption chiller of 12 kW nominal power was characterized with different mathematical correlations built with Multivariate Linear Regression (∆∆t'), and Multivariable Polynomial Regression (MPR). The curve parameters were modified to find the best fit of the experimental data, which were evaluated using Root Mean Square Error (RMSE). MPR was the best fit, calculated only based on inlet temperatures. Once the heat curves were obtained in different parts of the absorption chiller (evaporator, generator and absorber-condenser), the actual cooling capacity delivered by the absorption chiller was assessed against the chilling requirements of the fruit. The operating conditions for the cold room and absorption chiller were then determined so that fruit could be kept at 2°C. The operating conditions for the absorption chiller were -2°C at the evaporator outlet and 25°C in the entry of the absorber, while the temperature in the generator was determined by the curve, which defines the temperature required to supply the chilling requirement of the cold room plus a five percent loss. Finally, four dynamic simulations of the solar-powered absorption refrigeration system were carried out in TRNSYS. The simulations counted with a field of solar collectors (FPC or ETC), a heat storage tank, an auxiliary heat system connected in series or series-parallel to the storage tank, a cooling tower, a cold room with 240 trays of sweet cherry at 2°C and an absorption chiller. The TMY used in the simulations varied depending on the city to be evaluated. Moreover, the solar field area varied from 40 to 240 m2 in the four simulations for the three cities. The solar fraction generated and the auxiliary heat used were also evaluated. It was found that the series-parallel connection with FPC collectors is the one that generates the highest solar fractions and the lowest consumption of auxiliary heat in the three cities evaluated. In addition, it was determined that the city that presents the highest consumption of auxiliary heat is Santiago since it presents a higher chilling requirement under the same operating conditions of the chiller. This occurs due to the extreme temperatures occurring in summer. However, if the auxiliary heat were supplied by an LPG boiler and if we consider that fuel in Santiago is, on average, $ 70 cheaper per liter than in the other two cities, it can be stated that Santiago is the city with the lowest costs associated with auxiliary heat consumption. Solar fraction averaged 0.56 for the three cities in the simulation for the FPC collectors of 80m2 connected in series-parallel, with LPG costs associated with the operation from October to March reaching $3,084,402, $2.807833 and $3,041,813, for Antofagasta, Santiago and Chillán, respectively. As the machine is in operation 24 hours, the consumption of gas is high. Therefore, it is necessary to find a way of operation that allows preserving fruit and operate the absorption chiller only during daylight hours. This explains why the use of this type of cooling systems is mainly used for air conditioning and not for food preservation.esCC BY-NC-ND 4.0 DEED Attribution-NonCommercial-NoDerivs 4.0 InternationalAire Acondicionado SolarConservación de FrutasRefrigeración de AlimentosTesis