Estudo experimental e modelo de simulação do inventário de refrigerante em uma bomba de calor a CO2 dotada de evaporador solar

Abstract

Faced with the serious water crisis faced by the world in recent decades, and considering that in Brazil, until the year 2021, hydroelectric plants were responsible for more than half of the country's energy generation, the use of heat pumps assisted by solar energy is presented as an alternative for the reduction of electrical energy consumption. However, they operate loaded with refrigerants, notoriously known as substances harmful to the environment, and in this way, carbon dioxide becomes a viable and ecologically correct option. The performance of this equipment is critically linked to an appropriate refrigerant charge, which, specifically for carbon dioxide, shows up as a gap in the studies promoted on Solar Energy Assisted Direct Expansion Heat Pumps (DX-SAHP). Therefore, the main objective of this work is the development of a mathematical model to simulate the functioning of a DX-SAHP operating with carbon dioxide in the transcritical cycle, in steady state, allowing to predict the ideal amount of refrigerant mass to be loaded in the equipment, in order to maximize your COP. Therefore, the main objective of this work is the development of a mathematical model to simulate the functioning of a DX-SAHP operating with carbon dioxide in the transcritical cycle, in steady state, allowing to predict the ideal amount of refrigerant mass to be loaded in the equipment, in order to maximize your COP. The model results were validated from 50 experimental points, under different levels of solar irradiation, considering the pressures of the refrigerant fluid in the evaporator and in the gas cooler, its temperature at the outlet of the gas cooler, the water temperature and the heat pump COP. As for the refrigerant fluid inventory, the model showed that the gas cooler is the component with the highest amount of mass, approximately 45.7% of the total and that, with the passage of the heat pump from the shade to the sun, about 5.4% of the mass migrated from the high-pressure region to the low-pressure region. Thus, it was concluded that the equipment must work with a mass of refrigerant between 620 and 655 grams, regardless of the level of solar irradiation. Operating under these mass conditions its COP reached maximum values of 2.81, with the heat pump in the sun, and around 1.87, working in the shade.