Optimization of mixed working fluids for a novel trigeneration system based on organic Rankine cycle installed with heat pumps

A novel combined cooling, heating and powerorganic Rankine cycle (CCHP-ORC) system installed with heat pumps is presented in this paper. The CCHP-ORC system using zeotropic mixtures is first discussed, and this work is focused on selecting optimal zeotropic mixtures and determining the component concentration that gives a better performance. A system model under an idealized operating condition was built. The heat source is geothermal water whose temperature is 95 degrees C, and the mass flow is 40 t/h. The heat transfer fluid is heated to 45 degrees C for heating with the ambient temperature of -5 degrees C, and the refrigerating fluid is cooled to 0 degrees C with the ambient temperature of 35 degrees C In this paper, 20 zeotropic mixtures were analyzed. The evaluation index net output power, heating capacity, refrigerating capacity, coefficient of performance (COP), economic thermal efficiency and exergy efficiency were calculated with the changing evaporation temperature under the condition of ejector coefficient 0.2. The ejector coefficient and evaporation temperature had been analyzed as independent variables. The results showed that R141b/R134a, R141b/R152a and R123/152a have a higher COP and exergy efficiency than others. By analyzing the component concentration of the optimized three kinds of zeotropic mixtures, it can be inferred that a mixture of dry and wet working fluids is more suitable for the system. The system gives rise to higher energy output if zeotropic mixtures are made of a higher proportion of wet working fluid and a lower proportion of dry working fluid. (C) 2015 Published by Elsevier Ltd.