Over the last few years, environmental protection has become a major concern for all businesses and organisations. Carrefour Market’s management therefore wished to make this ecological notion part of its technical specifications for its new store at Jacques Cœur, in Montpellier, France. To respond to Carrefour Market’s explicitly ecological approach, Teissonnière designed a refrigeration system in compliance with Carrefour’s special technical specifications aiming at limiting its environmental impact as much as possible. It therefore performed its first cascade R134a/CO2 system installation. The R134a with a direct expansion valve cools the cold storage rooms and the refrigerator cabinets, whereas the CO2 cools the walk-in freezer and freezer units.
R134a was chosen over R404A because of its excellent thermodynamic properties and its lower Global Warming Potential (GWP).
As for the CO2, it is in full compliance with the special technical specifications. It is a natural refrigerant with a low impact on ozone layer degradation and a GWP index of 1. Bernard Abrax, Teissonnière’s manager, also insists in CO2’s excellent volumetric efficiency, which entails smaller diameters in the piping (a sizeable advantage as the price of copper soars) and a lesser load of refrigerant. CO2 offers a high energy output and is still less expensive on purchase than other HFC refrigerants.
But however attractive CO2 may be, it is a complex refrigerant to handle. The major difficulty for its use is the high working pressure it requires. Since CO2 isn’t at present commonly used, contractors also face a serious lack of resources for choosing the equipment. Teissonnière therefore decided to work with Danfoss on this project because this Danish group offers complete CO2 solutions and has solid experience in designing CO2 systems. Danfoss teams thus contributed to the project’s successful implementation by providing Teissonnière with guidance for the choice of the specific CO2 equipment as well as for optimizing the system’s settings.
The Danfoss ADAP-KOOL® series was therefore chosen. Both central refrigerating units are equipped with pack controllers AK-PC controls (AK-PC 840 for the refrigerating and AK-PC 740 for the freezing) that enable a floating HP and pilot the AKD frequency converters in order to adjust out put to the refrigerating needs and thus limit the central units’ electricity consumption. The AK-PC also commands the condensers’ motor fans. They therefore contribute to reducing the refrigerating system’s sound power level. This is critical since the machine room is only a dozen meters away from the neighbouring residences.
Regarding the refrigerating and freezing units’ regulation, AKV electronic expansion valves were installed on both systems. They are piloted by AK-CC 550 regulators for the R134a refrigerating and by AK CC 550A CO2-specific regulators for the CO2 freezing. This electronic expansion valve regulation enables optimum filling of the evaporators since the auto-adapting superheat is kept under control. Seasonal temperature changes (summer/winter) therefore don’t have an impact on the refrigerating units’ regulation.
Conclusion
The system has been running for a year now and it has been a very positive experience for the contractor. The system’s maintenance is the same as an HFC system. Bernard Abrax considers that once the learning phase is over, a CO2 refrigerating system is similar to standard systems. CO2 is thus likely to become more widespread and accessible.