Minimizing COP loss from optimal high pressure correlation for transcritical CO2 cycle

•Optimal high pressure correlations of transcritical CO2 cycles are reviewed.•Error propagation from optimal high pressure correlation to COP causes big COP loss.•A COP loss minimization method is proposed to restrain the error propagation.•COP loss of single-stage CO2 cycle is reduced from 71% to 0.7% with the new method.

CO2 transcritical cycle has been successful applied in many refrigeration and heat pump systems. High pressure optimization and control play a critical role in maximizing COP (coefficient of performance) of CO2 transcritical systems. This work reviewed optimal high pressure correlations of transcritical CO2 cycles in open literature and found a potential significant COP loss near the critical pressure due to error propagation from optimal high pressure approximation to actual COP. Therefore, a COP loss minimization method is proposed to restrain the error propagation and obtain more robust high pressure correlation. Case study on the single-stage CO2 transcritical cycle demonstrated that the maximum COP loss from the conventional high pressure optimization method can be significantly reduced from −71% to −0.7% using the new method.