In North America, transcritical booster systems using only CO2 have been implemented largely in conventional supermarkets. By contrast, in Japan the uptake of transcritical systems has been most evident in smaller convenience stores.

Convenience stores have not gone to transcritical in the U.S. because they are much more expensive,”

Andre Patenaude, Director, CO2 Business Development for Emerson Climate Technologies.

However, judging by the new components on show at the AHR Expo, this could be about to change.

All-in-one CO2 transcritical controller from Danfoss

Danfoss showcased a CO2 transcritical controller, the AK-PC 772, designed for smaller formats. The all-in-one unit oversees compressors, gas cooler, oil, receiver, electronic expansion valves and heat reclaim.

Danfoss is trying to reduce the complexity of CO2, which is already a complex concept to begin with,” said Jae Chon, OEM Key Accounts Manager for Danfoss. “By combining all processes into a single platform, this controller handles medium-temperature and low-temperature compressors, and a cooling algorithm for gas cooler control, including a high-pressure valve and a flash gas bypass valve.”

CAREL explores the concept of a CO2 transcritical controller for convenience stores

At the AHR Expo, CAREL introduced its pRack pR300T controller, which uses a single electronic board to fully manage a self-contained transcritical system with a triple suction line, heat recovery, gas cooler, high pressure valves, liquid receiver and intercooler. The controller and system are suited for convenience store applications.

CAREL‘s compact solution for COcompressor rack control and management meets market requirements regarding:

  • Control of low- and medium-temperature compressors
  • Transcritical valve synchronisation through a directly integrated driver
  • A third suction line control for a parallel compressor, which can improve a transcritical system’s efficiency in warmer climates
  • Management algorithms for energy savings
  • Dedicated algorithms for CO2 systems management
  • Integration with heat recovery systems

In these types of systems, where each individual function is intrinsically linked to the others, the control device needs to independently manage all the operating stages of the unit. The pRack pR300T can manage and synchronise the operation of all fundamental components making up the system through just one individual device,” 

Nicola Pieretti, Application Specialist – Retail Solution, Marketing Dept. at CAREL.

Sanden’s inverter scroll compressor being tested by 7-Eleven  

Meanwhile, Sanden showed a hermetic inverter scroll compressor for CO2 transcritical refrigeration in convenience store formats. It contains a compressor, condenser and air-to-air microchannel heat exchanger in a box that typically resides on a store’s rooftop, and connects to multiple evaporators in cases.

The unit is being tested by 7-Eleven in Japan in 73 stores, said Larry Hieb, vice president of engineering, Sanden. It has not yet been approved for use in North America.  

Emerson launches new semi-hermetic compressor

Emerson also announced a new compressor designed for smaller retail formats like convenience stores, the Copeland semi-hermetic compressor for transcritical CO2 with 5-, 7- and 9-horespower. It has integrated high- and low-pressure valves with low sound and vibration. Previously Emerson offered the system in 12-, 15- and 30-horsepower units.