Field measurements and comparison of supermarket refrigeration systems.


In this study, supermarket refrigeration systems with CO2 as refrigerant are evaluated and compared to conventional systems with HFCs. The aim was to compare 6 systems based on field measurements and computer simulation models which have been developed in parallel to the testing. Three supermarkets using CO2 as refrigerant have been studied and out of those were two trans-critical systems and one was a cascade system with R404A in the high stage. The reference conventional systems can be considered best practice systems with advanced control and robust design. Carbon dioxide has many advantageous properties as a refrigerant; it is environmental friendly, easily accessible and cheap, it has good thermal properties and allows the piping to be reduced in size. The main challenge is that CO2 works with high pressures and has a low critical point of 31°C. If the CO2 operates at higher temperatures than 31°C it will be trans-critical, this is not as critical as it sounds but implies some challenges. The conventional systems are indirect on medium temperature and work with R404A and partly R407C as refrigerant. The secondary refrigerant is propylene glycol. In the low temperature applications solely R404A is used in direct expansion. All motors serving compressors, pumps and fans are frequency controlled. Further the systems have floating condensing and evaporating temperatures. The field measurements conclude that there is still improvement potential for the trans-critical CO2-systems. They require improvement to reach the most advanced "conventional" systems on the market. The conventional solutions showed 20-25% higher COP on a system basis. However, the required improvement for the CO2-systems is within close reach. With the aid of computer simulation modelling, it is shown that the CO2-systems should be able to reach or exceed the efficiency of the conventional systems if applying; internal subcooling (subcool freezer condensate), improved heat exchangers (lower temperature differences), improved controllability (more stable operation = lower temp difference). Further the inherent advantages of CO2 systems should be utilised such as direct use on cold and warm side; thus avoiding extra temperature differences.

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  • Original title: Field measurements and comparison of supermarket refrigeration systems.
  • Record ID : 2011-0227
  • Languages: English
  • Subject: HFCs alternatives
  • Source: IIR/Eurotherm sustainable refrigeration and heat pump technology conference. Proceedings of the Eurotherm Seminar No. 88, Stockholm, Sweden, June 13-16, 2010.
  • Publication date: 2010/06/13


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