Abstract: Transcritical CO₂ systems lose efficiency in extreme heat through high-pressure expansion and flash-gas recompression. A rotary pressure exchanger (PX) recovers part of the expansion work by using the dense gas-cooler outlet stream to compress receiver vapour inside rotating ducts. This study evaluates a supermarket booster with 100 kW medium-temperature and 25 kW low-temperature loads in four configurations: flash-gas bypass (FGB), parallel compression (PC), PX with flash-gas bypass (PX), and PX combined with parallel compression (PX + PC). A reduced-order model based on constant-pressure displacement of the driven vapour and the Span–Wagner equation of state is coupled to the booster model. High-side and receiver pressures are optimised from 0 to 52 °C. Component exergy destruction is evaluated for each layout, while 8784 hourly weather observations from 2024 at Kuwait International Airport and Ali Al Salem, Kuwait, provide the basis for annual performance. At 45 °C, PX + PC achieves a COP of 1.66, compared with 1.37 for PC and 1.14 for FGB, while total exergy destruction falls from 85.7 kW in FGB to 51.8 kW. Annual electricity use falls by 11.7% relative to PC and 24.0% relative to FGB. Peak power is reduced by up to 24.2% relative to PC, and hours of operation at the 120 bar high-side limit fall by 87–88%. Volumetric effectiveness has the greatest influence on annual savings: effectiveness of 0.7–1.0 gives savings of 9.2–13.0% relative to PC. The results support pairing a PX with parallel compression for efficient CO₂-only commercial refrigeration in extreme heat.