What is Parallel/Interstage Compression in CO2 Transcritical Booster Systems

The purpose of a parallel/interstage compressors in a transcritical CO2 system is to increase the system efficiency in warm ambient locations like Australia, South Africa, and Mexico. Any place on the planet where the temperatures are above 87.8F/31C for most of the year parallel/interstage compression could be an option.

When you have a running CO2 booster system (booster really means that the low temperature compressors are discharging into the medium temperature suction Learn How a Booster System works Here) on a very warm day the system produces a huge amount of flash gas (which really means the system is producing more CO2 vapor/gas then liquid) and this vapor/gas is going into the flash tank/receiver. That flash gas goes from the flash tank/receiver back to the medium temperature suction and when this happens there is a huge amount of load and work put on the medium temperature compressors. This extra refrigerant load cost more money on those hot days. I saw some calculations where the system would of produced up to 50% flash gas.

There are many different warm or high ambient strategies, and parallel/interstage compression is just one. When you install a parallel/interstage compressor on a booster system, instead of sending that flash gas (refrigerant vapor) from the flash tank/receiver back to the medium temperature suction it will go to the parallel (PC)/interstage (IT) compressors. This compressors suction will be pipe separately from the medium temperature compressors and in doing that you can run it at a higher suction pressure then the medium temperature compressors. When you do this compressors can be smaller, the compression ratio is reduced, you have less work on the medium temperature compressors and you have a good potential to reduce your energy costs.

Watch this tutorial on Parallel Compressors - Watch Here

All in all this is just one of many warm/high ambient solutions. The most important thing you need to know is this the right solution for your application. Also, in cold climates where it does not get above 87.8F/31C very often, you will probably not see many of these as those system will produce significantly less flash gas.

If you want to learn more about different warm/high ambient strategies check out this podcast on High Ambient Strategies LISTEN HERE I did with Andre Patenaude, CET from Copeland

Learn more about Refrigeration Mentors CO2 learning programs HERE