EIA: Notable progress in retail use of CO2
31 March 2011
CO2 winners at 2011 ACR News Awards
05 April 2011
The project “expander compressor unit (ECU) for carbon dioxide refrigeration systems with hot gas defrosting”, which received the 2nd place in the category “climate-friendly special applications in refrigeration”, was a co-operative initiative between Saxony-based kke GmbH Kesselsdorf and the BITZER Chair of Refrigeration, Cryo and Compressor Technology of the Technische Universität Dresden. Other companies involved in the project were TEKO, Wurm Elektronische Systeme, thermofin, Danfoss, Viessmann and Küba.
About the project
kke GmbH built a transcritical CO2 booster refrigeration system connected to a demonstration store that simulated a sales area of approximately 850-1000m².
The main components of the system are:
- two frequency controlled subcritical compressors for TK (t0 = -30 °C) from Bitzer
- two frequency controlled transcritical compressors for NK (t0= -10 °C) from Bitzer
- liquid /vapor separator
- air cooled gas cooler and intermediate cooler from thermofin GmbH
- internal heat exchanger
- expander compressor unit (ECU)
- coriolis mass flow meters
- hot gas defrosting
The ECU unit expands the CO2 from high pressure to middle pressure (li./v. separator) and in a second expansion stage the flash gas. The expansion stages are direct coupled with a compression stage. This additional compression stage allowed to also integrate an intermediate cooler (see fig. 2). With such a unit the energy consumption and the discharge temperature of the main compressors can be reduced.
Another means of reducing energy consumption is through hot gas defrosting. While in conventional refrigeration systems, additional electrical heating is used to defrost the evaporators, the use of hot gas defrosting can save this energy. Moreover, the excellent heat transfer characteristics of CO2 allow a much quicker defrosting. First tests have confirmed feasibility and verified the predicted energy savings.
In addition, the system is used by kke GmbH to train its staff and for customer demonstrations.