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.