Carrefour has invested around €150 million in phasing down HFCs and replacing them with CO2 systems since 2015.
The system at the Nichelino store uses parallel compression, heat recovery for tap water and facility heating (400 kW) and liquid and gas ejectors.
It was designed by Swiss refrigeration consulting and engineering company Frigo-Consulting, at the system’s heart are two booster racks conceived to provide 360 kW of medium-temperature (MT) refrigeration at -2°C and 72 kW of low-temperature (LT) refrigeration at -26°C.
The racks supply a sales area of 7,500m2 featuring 380m of cabinets and 570m2 of refrigerated rooms.
“The gas and liquid ejectors, combined with the parallel compression, facilitate savings in energy consumption, because they are reducing the compressors’ work and the throttling losses on the high-pressure valve,“ Dario Agostini, project manager in charge of the Nichelino installation at Frigo-Consulting, told Accelerate Italy.
“Don’t forget the huge environmental benefits.“Dario Agostini, Frigo-Consulting
The pressure difference between the high-pressure side and the liquid receiver allows the ejectors to convey liquid and vapour CO2 to the receiver, without requiring any additional energy.
“Through liquid ejectors, it is possible to overflow the evaporators: the CO2 in the liquid phase has a notably higher heat transfer capacity than it does during the gas phase,” Agostini says.
Consequently, based on the evaporator’s potential, the evaporation temperature could increase from -7°C to -2°C on the MT side and from -30°C to -26°C on the LT side. “This leads to further reductions in the compressors’ work, and, ultimately, to an electrical energy consumption reduction,” Agostini says.
In Nichelino, the average year-round ambient temperature is 12.8°C. Similar installations in place in nearby Switzerland have delivered electricity consumption savings of 25% compared to a traditional booster system with parallel compression.
“Don’t forget the huge environmental benefits,” says Agostini. The system reduces the store’s carbon footprint by reducing both direct and indirect emissions – achieving the former by switching from R404A (whose GWP is 3,922) and R134a (GWP: 1,430) to CO2 (GWP: 1), and the latter thanks to “the advanced refrigeration and the reduced energy heating request”.
By using transcritical CO2 systems instead of conventional HFC options, Carrefour has achieved previous energy savings of 8-12% in warmer regions such as southern Spain, and savings of 18-20% in areas with more temperate climates such as Brussels or Paris.
In October 2017, the Nichelino hypermarket received an award for the ‘most sustainable shopping centre’, within the framework of the international SBChallenge, organised by an EU-funded research project.