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Parallel compression enhances the performance of the transcritical CO2 systems during periods of warm ambient and also during winter heat recovery operation where condensing pressures are elevated on purpose. By having a dedicated compressor being fed gas from the top of the flash tank which is at a higher pressure than the suction manifold of the other Transcritical compressors, less work is required (due to lower compressions ratio) by the parallel compressor thereby improving the overall system efficiency.
Emerson commercial CO2 handbook – https://climate.emerson.com/documents/commercial-co2-handbook-en-us-5127714.pdf
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