**7. Conclusion and outlook**

This book chapter proposes a virtual technique for the selection of low-GWP working fluids for the ORC system. The criteria for working fluids selection and simulation approach for assessing the cycle performance were introduced to the reads in detail. The selection criteria mainly include the chemical property (critical, boiling, and triple temperatures), thermodynamic property (Vaporization latent heat, density, heat capacity, phase equilibrium, etc.), transport property (dynamic viscosity and thermal conductivity), environmental property (low GWP and zero ODP), and safety (non-toxic, non-flammable). Depending on the application and the level of temperature of the heat source, no perfect fluid exists. It is important to proceed to a selection by considering the different characteristics of the sources and the application. In general, the differences between the cycle efficiencies of the working fluids are not very significant if the selections based on critical and boiling temperatures are correctly realized. For further investigations, it will be of interest to size the different

*Utilizing Computational Methods to Identify Low GWP Working Fluids for ORC Systems DOI: http://dx.doi.org/10.5772/intechopen.1003740*

components in the cycle. It concerns the design of heat exchangers or turbine or pump based on the estimation of transport properties of the working fluid. The thermodynamic performance of ORC systems can be improved by modifying its architecture using a regenerator as presented in our example or removing a part of the working fluid circulating in the turbine into the mixing heater. In consequence, the analysis of the performance of working fluid has to be remade. Moreover, the thermodynamic performance of ORC systems can be improved by using zeotropic mixtures as the working fluid. A zeotropic working fluid with a temperature glide of 5°C or greater can improve the efficiency and performance of the thermodynamic cycle by matching the temperature glide between the heat transfer fluid and the working fluid in a counterflow heat exchanger. This kind of matching, so-called temperature glide matching, can maintain the temperature difference between the heat exchange fluid and the working fluid in a constant, thereby reducing the irreversibility in the heat transfer process, improving performance and energy and exergy efficiency.
