A supermarket in Verona, Italy, has cut its HVAC energy use by 40% by integrating its heating and air-conditioning into its CO2 (R744)-based refrigeration system, according to Enrico Zambotto, Technical Engineering Director of Refrigeration Systems at Italian OEM Arneg.
Compared with operating an independent HVAC system, which would require around 68,000kWh annually, the store’s integrated HVAC system uses only 41,000kWh a year. In total, the supermarket’s refrigeration and integrated HVAC system uses roughly 135,000kWh a year.
The energy savings largely come during the winter months when the 1,670m2 (17,975ft2) supermarket benefits from “free heating” that is sourced directly from its CO2-based refrigeration system’s waste heat, he explained.
Based on a cost of €0.40 (US$0.43) per kWh, this represents annual savings of approximately €11,000 (US$11,800), he added.
Zambotto shared details of this case study during his presentation in a refrigeration session at the ATMOsphere (ATMO) Europe Summit on natural refrigerants. The conference took place November 15–16 in Brussels and was organized by ATMOsphere, publisher of R744.com.
“Driven by the increased restriction of the f-gas application and with the aim of raising the efficiency of the buildings, more and more customers are looking for the integration of refrigeration system with HVAC,” said Zambotto.
“This trend is also helped by the application of CO2 that, with a high discharge temperature, grants good efficiency for hydronic heating systems,” he added.
“This trend is also helped by the application of CO2 that, with a high discharge temperature, grants good efficiency for hydronic heating systems.”Enrico Zambotto, Arneg
According to Zambotto’s presentation, the supermarket requires 60kW (17TR) of capacity for its medium-temperature (MT) cabinets, 4kW (1TR) for its low-temperature (LT) cabinets, 72kW (20TR) for heating during the winter with a minimum ambient temperature of -7°C (19.4°F) and 66kW (19TR) for air-conditioning during the summer with a maximum ambient temperature of 37°C (98.6°F).
To meet these needs, Arneg installed a CO2 rack that provides 158kW (45TR) cooling capacity for MT and 7kW (2TR) cooling capacity for LT.
Heating throughout the year
Throughout the year, heat rejected from the supermarket’s refrigerated cabinets is used to produce hot water for the store, and during the winter, it’s used to heat the building, Zambotto explained. When heating needs exceed what can be produced by the refrigeration system’s waste heat, an external evaporator helps to meet demand.
The additional evaporator can be integrated with the system’s gas cooler to reduce space and help with system defrost, he added.
During the summer, part of the store’s cooling demand is met by its open multideck cabinets.
Additional air-conditioning load is supplied by a dedicated refrigeration system that has been added to the compressor rack, said Zambotto.
According to Zambotto, the integrated HVAC system costs around €23,000 (US$24,700) more than a “standard” system. However, given the savings on energy cost realized by the integrated HVAC system, it has a payback period of just over two years. The return on investment will likely be higher as energy costs increase.
To date, Arneg has installed integrated HVAC&R systems at 90 stores, Zambotto said. This represents around 10% of its supermarket projects. Around 60% of its supermarket projects utilize at least heat recovery for hot water production.