Preliminary experimental investigation on a transcritical R744 condensing unit using the novel PWM ejector

Paride Gullo*, Martin Ryhl Kærn, Michael Birkelund*, Ekaterini E. Kriezi

*Corresponding author for this work

Research output: Chapter in Book/Report/Conference proceedingArticle in proceedingsResearchpeer-review


In this work the preliminary experimental performance study on an innovative control technique for two-phase ejectors in transcritical R744 condensing units is presented. Currently two-phase ejectors cannot be properly capacity controlled without sacrificing ejector and system efficiency in these units. The novel capacity control methodology involves the pulse-width modulation (PWM) of the refrigerant flow through the ejector. At the compressor speed of 50 Hz, water temperatures at the gas cooler inlet between 30 °C and 40 °C and R744 evaporating temperature of roughly -5.5 °C, the collected data revealed that the discharge pressure can be appropriately controlled as well as increased by up to about 28 bar. Also, at the optimum operation conditions the unit with the PWM ejector presented enhancements in coefficient of performance (COP) by between 10.0% and 12.1% over the system using the passive ejector and by between 23.7% and 31.2% compared to the solution with flash gas by-pass valve. Finally, the proposed methodology presents low cost, simplicity, low vulnerability to clogging and much more significant potential than its today’s available competitors.
Original languageEnglish
Title of host publicationProceedings of the 14th IIR-Gustav Lorentzen Conference on Natural Refrigerants
PublisherInternational Institute of Refrigeration
Publication date2020
Article number1001
ISBN (Electronic)978-2-36215-040-1
Publication statusPublished - 2020
Event14th IIR-Gustav Lorentzen Conference on Natural Refrigerants (GL2020) - , Japan
Duration: 7 Dec 20209 Dec 2020


Conference14th IIR-Gustav Lorentzen Conference on Natural Refrigerants (GL2020)
Internet address
SeriesScience et Technique du Froid

Bibliographical note

Copyright © IIF/IIR. Published with the authorization of the International Institute of Refrigeration (IIR):


  • Carbon Dioxide
  • Commercial Refrigeration
  • Expansion Work Recovery
  • Gas Cooler Pressure Control
  • Small-capacity System


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