Metro AG, a German wholesale retailer, has installed its first transcritical CO2 solutions in two existing stores in Bulgaria, with each achieving a 26% energy reduction on cooling, and additional savings on heating and hot water.

The two new installations, in Sofia and Ruse, each include a booster system with ejector technology, and heat recovery to produce heating and hot water for the stores. The Sofia store was refurbished in 2018, and the store in Ruse followed in 2019.

The Sofia store is 8,386m2 (90,266ft2) with a total medium-temperature capacity of 556kW (158.1TR), and low-temperature capacity of 130kW (37TR). The Ruse store is a bit smaller, at 6,199m2 (66,725ft2), with 484kW (137.6TR) medium-temperature capacity and 116kW (33TR) low-temperature capacity.

The new CO2 systems are much more efficient than the old HFC ones. In its first full year of operation, the Sofia store achieved a 400,000+ kWh savings, equaling 26.45% reduction.

The newer Ruse system hasn’t yet been in operation for a full year, but during a four-month period from October 2019 to January 2020 the store achieved a saving of 26.26% (when compared to the same period one year before).

The heat recovery feature has also led to significant financial savings, with Metro saving €36,901 (US$40,718) on store heating and hot water production in the Sofia store in 2019, and €11,622 (US$12,824) in the four-month period from October 2019 to January 2020 in the Ruse store.

Additional energy saving features include doors on all medium-temperature cabinets and LED lighting.

Racks outside

The CO2 racks are located in containers outside the building. This was necessary because the existing machine rooms didn’t have room to install the new systems with the old ones still in place. The vacated machine rooms now house the heat recovery features for the new systems.

Without incurring any downtime, installing the new systems with the old ones still operating was a challenging task. The Sofia store is open 24/7 while the Ruse store is open from 6am to 9pm every day, meaning that the installation teams worked mostly night shifts to minimize any disruption.

Metro also used temporary plug-in cabinets during the exchange of the old cabinets, to minimize any disruption to the customers.

The project was carried out in collaboration with the Swiss consultancy Frigo-Consulting. Frigo did the system specifications, commissioning and quality inspections of the installed solutions. Carrier was chosen to deliver the systems – Carrier’s CO2OLtec solution – after a tender procedure.

Metro has a total of 11 stores in Bulgaria. Three of these have R134a/CO2 cascade systems, which were installed because full CO2 systems for “reliable operation” in hot climates weren’t available at the time, according to Metro.

Of the remaining five, three have been converted from R404A to R448A or R449A, and two are still running on R404A and R422D.

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