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Definition and performance simulations of a novel solar-driven hybrid absorption-thermochemical refrigeration system

Fitó, Jaume, Coronas, Alberto, Mauran, Sylvain, Mazet, Nathalie, Stitou, Driss
Energy conversion and management 2018 v.175 pp. 298-312
absorption, condensation (phase transition), energy, evaporation, heat, lithium chloride, refrigeration, refrigerators, screening, solar collectors, sorbents, temperature, Spain
This paper proposes a novel hybrid refrigeration system with energy storage, driven by low-grade solar heat and consisting of a single-stage absorption cycle coupled with a thermochemical process by sharing the same condenser, evaporator and refrigerant fluid. A first screening of ammonia-based working pairs for evaporation temperatures of −10 °C, condensation temperatures of 30 °C and heat source temperatures of 80 °C reveals LiNO3 as suitable sorbent salt for the absorption subsystem, and BaCl2, PbBr2, SrCl2, LiCl, NH4Br and SnCl2 as candidate reactive salts in the thermochemical subsystem. The subsequent parametric study indicates that the absorption subsystem with NH3/LiNO3 reaches close-to-maximum COP at the indicated conditions, and the thermochemical subsystem delivers its highest COP with the NH3/BaCl2 pair. Then, the power-storage and performance-storage relationships of the thermochemical subsystem are analyzed for the NH3/BaCl2 pair with respect to variations in operating conditions and several implementation parameters of the reactive composite. Finally, the performance of the hybrid system with the (NH3/LiNO3 + NH3/BaCl2) pair combination is compared to its subsystems against a variable demand profile calculated from climatic data of July in Barcelona, Spain. A novel indicator is defined to assess demand coverage: the Coefficient of Satisfaction of Demand (CSD). Depending on solar collector field area and amount of refrigerant storable by the thermochemical subsystem, the hybrid system reaches up to 24% higher CSD than the reference system (a solar single-stage absorption refrigerator with no storage), and at least 14% higher COP than the thermochemical process.