CO2 as a Refrigerant – Retail Booster Systems

This is post number ten of a series.

Retail Booster Systems

Two-stage compression is used for transcritical low temperature applications because the discharge temperature of R744 is high and will potentially result in lubricant breakdown. Figure below shows a simple two-stage booster or externally-compounded system:

The refrigerant from the low-temperature loads is drawn into the low-stage compressors. The discharge from these compressors goes into the suction of the high-stage compressors.

The refrigerant from the medium-temperature (MT) loads is drawn into the suction of the high-stage compressors. The refrigerant from the receiver pressure-regulating valve is also drawn into the suction of the high-stage compressors. The flash gas from the receiver pressure-regulating valve and the suction gas from the medium temperature loads provide some interstage cooling. This is usually enough to maintain the discharge temperature of the high-stage compressors below the level at which the lubricant will deteriorate. Additional interstage cooling can also be provided if required.

In the next article of this series we’ll take a closer look at retail cascade systems.