This allows the system to run subcritically in the warm summer months, and reduces the electricity consumption of the compressors, said Crea.
The groundwater used as a cooling fluid in the system is 15-20°C (59-68°F) warm year round. This allowed Crea to set a 25°C (77°F) condensing temperature in the system, using a plate heat exchanger. The use of groundwater, instead of air, to condense the CO2, allows the system to run in subcritical mode even during the hottest summer months when the ambient air temperature is 27-28°C (80.6-82.4°F) or more, Crea said.
The 400m2 (4306ft2) remodeled store was officially opened in December 2019, after a two-month refurbishment period. Crea did not name the retailer.
In the winter months the system is designed to run in transcritical mode to satisfy the supermarket’s need for hot water. To achieve the needed hot water, the system employs heat recovery, which can recover up to 42kW in winter, equaling “total” heat recovery, and increasing the system’s COP to 4.2, according to Stefano Tortorici, Technical Engineer at Crea.
Crea experienced several challenges in designing the system, including limited space and local noise level requirements. The store is located in a building in the historical center of Milan, with a narrow technical room in the basement. The narrow space issue was solved via integration of the air conditioning in the main rack. The high-temperature compressor used for air conditioning also doubles as a parallel compressor, disposing of flash gas accumulated in the receiver. The central location, near the Milan Cathedral, also meant that strict noise-level limits were imposed.
The capacity of the Milan system is 30kW (8.5TR) for medium temperature, 6kW (1.7TR) for low temperature and 40kW (11.4TR) for high temperature (air conditioning). The system contains six Frascold compressors, three medium temperature, two low temperature and one high temperature compressor. It has three Alfa Laval plate heat exchangers for the heat recovery, condenser and air conditioning. It also has a liquid receiver and Carel controls.
Crea declined to comment on the cost or ROI of the system compared to an HFC system, saying that the client for whom the project was designed has worked with natural refrigerants for several years, and that a HFC system was never considered for this store.