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RESUMEN Este trabajo presenta una caracterización de un sistema de refrigeración empleando la radiación solar como única fuente de energía para generar el fenómeno de la adsorción asistido en un colector estacionario tipo placa plana. Este colector presenta un área de captación de 1.1m2 trabajando con carbón activado como adsorbato y empleando metanol como adsorbente. Los resultados experimentales permitieron compararse en dos condiciones de trabajo cuya finalidad fue enfriar una pequeña cantidad de agua reservada de 2 litros. Se registraron temperaturas de generación en el colector solar por encima de los 50°C para intensidades solares por encima de los 800 [watt/m2]. El COP del sistema se presentó por encima de los 0,4 según etapas de enfriamiento y adsorción isobárica. Se realizaron mediciones de radiación solar, se tomaron mediciones de temperatura del sistema en funcionamiento, dando como resultados diferencias de temperatura de hasta 8,6 °C entre la temperatura ambiente y la temperatura de la recámara de frio. Se tomaron mediciones de radiación local de hasta 1155 [watt/m2], dando resultados de eficiencia de nuestro colector de hasta 75% en horas específicas y de 35% en eficiencia total diaria. Aprovechando herramientas a nivel de diseño de experimentos (DOE), por medio de superficies de respuestas se estimó un modelo del comportamiento en equilibrio termodinámico que se utilizará como referencia en futuros sistema de control. ABSTRACT This work presents a characterization of a cooling system using solar radiation as the only source of energy to generate the adsorption phenomenon assisted in a stationary flat plate collector. This collector has an area of 1.1m2 working with activated charcoal as adsorbate and using methanol as an adsorbent. The experimental results were compared in two conditions of tests with the objective to cool two liters of water. Temperatures of generation were recorded in the solar collector above 50 °C for solar radiation above 800 [W/m2]. The COP of the system presented values above 0.4, according to isobaric cooling and adsorption stages. Measurements of solar radiation, temperatures of the system were performed, resulting in temperature differences of up to 8.6 °C between the ambient temperature and the cold room. Local radiation samples of up to 1155 [W/m2] were obtained, showing efficiency of the collector up to 75%, at specific periods and 35% at total daily efficiency. Using the Design of Experiments (DOE), through response surfaces, a model of behavior in thermodynamic equilibrium to be used as a reference in futures control systems.

This study evaluates the performance of a cascade system in subcritical operation using the pair R744 / R134, 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, a thermostatic 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. Two parameters were manipulated: The superheating degree of the R744, 5-20 K, and the R744 compressor operation frequency, 40-65 Hz. In order to contribute to the improvement of the cooling processes, mainly about the sustainability and energy efficiency, a drop-in has been made at the high-temperature cycle, whose R134a load has been replaced by R404A. The alternative cooling system (R744 / R404A) was subjected to two stages of tests which allowed the energy comparison between the two refrigerant sets. Through the obtained results, it was estimated maximum COP equivalent to 1.36 and a minimum value of 1.06 for the R744 / R134a pair, demonstrating the applicability of this cascade system of variable thermal load conditions, the values ​​of capacity cooling, settled between 4.09 and 5.13 kW. The minimum value of the air temperature within the cold room was - 28 °C and -5 °C the maximum. Finally, it was found that the results obtained for R744 / R404A pair attended the air temperature condition inside the cold room with similar COP values. However, R744 / R404A pair operated at lower refrigeration capacities, these settled between 2.16 and 3.00 kW. This reduction is due to the large difference between the volumetric cooling capacity values of these HFCs in question, resulting in adaptation problems of the R404A to the compressor and the expansion mechanism.

This paper reports an experimental investigation using adaptive control in a refrigeration system. This system is composed basically of a semi-hermetic compressor, concentric tubes heat exchangers, the condenser and evaporator, and thermostatic expansion valve (TXV). The refrigerant used in the refrigeration system was the HCFC-22 and also an AC frequency inverter was used to control the speed of the compressor. The temperatures were measured by PT-100 sensors and the pressures using piezoresistive pressure transducers. Data acquisition was implemented using the Labview software. An electronic card with analogical signal output was also used. These analogical signals were converted into digital through a Programmable Logic Controller (PLC) and then sent to the computer through a PC serial port. Tests were performed with a variable speed compressor in the range from 30 to 70 Hz and the experimental results showed that the highest performance (COP) was attained by working in the range of 50 Hz, using adaptive fuzzy control.