Thermodynamic analysis of a cascade refrigerationsystem

In this study, energy, exergy, and cost analyses of cascade refrigeration system is investigated. Thermodynamic analysis is conducted for the Gaziantep city environment temperature for a fixed refrigerant couple. The cooling load, refrigerated space temperature and the temperatures during evaporation and condensations in all heat exchangers are considered to be constant. The operation and design parameters considered in this study include condenser fan velocity, evaporator fan velocity, isentropic efficiency of HTS compressor and isentropic efficiency of LTS compressor. Firstly, estimation of total cost including investment cost and operation cost at Gaziantep dead state by trade-off between the input exergy cost and capital (purchase) cost then determination of the effect of each parameter on total cost are conducted. Secondly determination of operation cost per year by means of the dead state temperature variation seasons gives a practical energy saving comparison basis. Results of the present thermodynamic analysis showed that; a minimum annual cost was found for the decision parameters such as LTS and HTS compressor efficiencies, air cooled condenser and evaporator fan velocities. The total annual cost of the cascade refrigeration system can be reduced by 30.86 percent in comparison to the medium range selected. The total annual operation cost of the system can be decreased by 11 percent in comparison with operation cost of initial design and the total annual cost can be decreased by 2.36 percent where the environment temperature variation taken into account. Finally the sum of annual cost saving about 33.22 percent according to the approach in this study.