At two new ALDI US locations, Italian control manufacturer Carel has tested total control and monitoring for each store’s transcritical CO2 (R744) compressor rack and propane (R290) plug-in spot merchandisers, with 15 new stores to be similarly equipped by year’s end.

The design and implementation of the control system was presented by Giacomo Favari, North American Refrigeration Marketing Manager at Carel, at the ATMOsphere America Summit 2023, held June 12–13 in Washington, D.C. The event was organized by ATMOsphere, publisher of

“By providing the monitoring system, we are able to build synergies among every single element of the system,” including heat reclaim, Favari said. However, as a distributed controller, it also allows elements to operate independently up to a certain level.

“We engaged with ALDI US because they wanted to acquire data, not only for the centralized [CO2] refrigeration system but also for some spot merchandisers using propane,” Favari said.

For the two test pilot stores, U.S.-based OEM Hillphoenix manufactured the transcritical CO2 racks ‒ “a typical booster system with low-temperature subcritical scroll compressors and transcritical medium-temperature compressors with reciprocating technology,” Favari noted. Austrian manufacturer AHT supplied the propane (R290) plug-in spot merchandisers.

For efficiency, the control boards communicate with the high-pressure valve, the flash gas bypass valve and an electronic evaporator pressure regulation (EEPR) valve installed in the system, he added.

“We used mechanical components provided by other vendors, proving that we can integrate multiple devices from other brands into our controller,” Favari said. In addition to the refrigeration equipment, Carel included the store’s wastewater vacuum collection system supplied by EVAC into its control system.

Two separate Modbus RTU (remote terminal unit) lines feed into the total-store-control supervisory system. One connects in the vacuum collection system and the spot merchandisers, equipped with Secop compressor controllers, and the other connects to the gas leak detectors, remote case and walk-in controllers and the rack controller, Favari said. “All that information flows into our monitoring system.”

“For reliability and safety, having a total store approach allows us to apply anti-liquid return and safe restore algorithms,” Favari said. The associated electronic expansion valve (EEV) shuts off when a suction group goes down. When the rack is restored, the controller staggers EEV operation during restart until the system returns to normal operation. If a CO2 leak is detected, the corresponding EEV shuts off to minimize loss.

With one controller, the store is able to visualize and interact with each element in the store on a 17in (43cm) touchscreen monitor. “Our open protocol strategy allows the information, stored in the supervisory [system], to be forwarded to a third-party digital platform such as IMS Evolve, ADT, Service Channel and Carel’s Red optimize platform,” he added. 

Bluetooth connectivity with case controllers allows field technicians to use apps for startup, commissioning and servicing, with remote OEM support capability, Favari said. “Servicing is one of the most important dimensions for transcritical CO2 systems,” he noted.

“With ALDI monitoring the energy data [from the two pilot stores], we are proceeding to deploy 15 more new stores in the second half of 2023,” Favari said, adding that the deployment indicates Carel’s controls are providing energy efficiency to the chain.

Lessons learned

“There was a lot of training involved in these [two] projects for multiple stakeholders that was made possible by our knowledge of natural refrigerant systems,” Favari said.

Those trained included various OEM departments, including engineering, sales, manufacturing, quality control and field services. Contractors and field service technicians received onsite training during system startup and commissioning.

Carel is in the process of creating a more structured training approach, Favari indicated. “We are building a contractor certificate program so that they can safely service our system, especially for transcritical CO2 technology.” In addition, the company is building an online training portal with “free access for anybody in the industry.”

The next step to further optimize the operation of the entire store is to integrate the HVAC system into the controller, Favari said, indicating that cooperation between the various groups involved in the store’s mechanics is in the works.

“When we are able to connect all these systems to our cloud platform, we will also apply artificial intelligence [AI] algorithms for prospective analytics to improve energy efficiency at startup and maintain efficiency over time,” Favari noted.

Headquartered in Brugine, Carel has installed over 11,000 natural refrigeration control systems since 2016. “Most of those systems are [for] CO2, but we also offer high-efficiency propane systems,” Favari said.

Awarded Best in Sector/Retail at the 2023 ATMOsphere America Summit, ALDI US also received the 2022 GreenChill Store Certification Excellence Award from the U.S. Environmental Protection Agency (EPA) as the food retailer with the most GreenChill-certified stores in the previous year. 

According to the chain’s 2022 sustainability report, nearly 500 ALDI US stores used CO2-based refrigeration systems. Over 100 additional stores were planning to apply for GreenChill certification by the end of 2022.

“By providing the monitoring system, we are able to build synergies among every single element of the system.”

Giacomo Favari, North American Refrigeration Marketing Manager at Carel