R744 Booster Transcritical
 

This model uses R744 (CO2) as a direct refrigerant in both the MT and LT systems. The LT compressors act as boosters to raise the vapour pressure to the level of the MT evaporators.

At ambient temperatures above approximately 23°C the compressors discharge the gas above the critical pressure of R744 (74 bar). The condenser then acts as a gas cooler and reduces the temperature of the discharge gas without condensing it into liquid. Cooled fluid passes through a pressure reduction valve, at which point a portion condenses into liquid and the rest remains as gas. Liquid and gas are separated in a flash vessel controlled by the pressure relief valve at a pressure of around 35 to 40 bar.

The liquid is then distributed to the MT and LT cabinets via the liquid line at this intermediate pressure. The flash gas is taken via an additional expansion device to the suction of the MT compressors. A separate flash gas compressor may be an adequate method to raise system efficiency in warmer regions.