LOW GWP WORKING FLUIDS FOR REVERSIBLE SYSTEMS OF HIGH TEMPERATURE HEAT PUMP AND ORGANIC RANKINE CYCLE (HTHP/ORC)

An innovative measure to recover low-grade waste heat is a reversible system based on a High Temperature Heat Pump (HTHP) and an Organic Rankine Cycle (ORC). This system can produce useful thermal energy and, in periods with no thermal demand, produce electricity. This study analyzes the influence of several working fluids (HFC-245fa, ammonia, isobutane, and HFO-1336mzz-Z) over the system using a theoretical model in basic and IHX cycles of HTHP/ORC architectures. The model has been optimized to use the more appropriate built-in ratio and the IHX effectiveness. Firstly, the built-in results highlight scroll and screw technologies as the most appropriate for the compressor-expander component and ammonia as the working fluid that requires minor size. Secondly, IHX effectiveness can be maximized for all the cases studied except for ammonia at lower evaporating temperatures. Finally, HFO-1336mzz-Z is the working fluid that leads to higher performance operating in both modes (net electrical efficiency for ORC and COP for HTHP).