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:

Simple booster system without oil management

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.

Andre Patenaude
Director – CO2 Business Development, Emerson Climate Technologies

Visit our website for additional information on CO2 Solutions from Emerson. 
Excerpt from original document; Commercial CO₂ Refrigeration Systems, Guide for Subcritical and Transcritical CO₂ Applications.

To read all posts in our series on CO2 as a Refrigerant, click on the links below:

1. Series Introduction
2. Criteria for Choosing Refrigerants
3. Properties of R744
4. Introduction to Trancritical Operation
5. Five Potential Hazards of R744
6. Comparison of R744 with Other Refrigerants
7. R744 Advantages / Disadvantages
8. Introduction to R744 Systems
9. Introduction to Retail Transcritical Systems
10. Retail Booster Systems
11. Introduction to Retail Cascade Systems
12. Introduction to Secondary Systems
13. Selecting the Best System