U.S. pharmacy chain Walgreens has deployed an integrated transcritical CO2 (R744) rack system at its flagship net-zero energy store in Evanston, Illinois, in an effort to boost energy efficiency and reduce operational costs.
Manufactured by U.S.-based OEM Zero Zone, the 38TR (133.6kW)-capacity Genesys CO2 Transcritical System delivers low- and medium-temperature refrigeration, air-conditioning, space heating and hot water, powered primarily by onsite solar panels, wind turbines and geothermal wells
Details of the installation were shared by Masood Ali, Global Refrigeration Manager at Zero Zone, during a case study presentation at the ATMO America Summit 2025, held June 11–12 in Atlanta, Georgia. The conference was hosted by ATMOsphere, publisher of NaturalRefrigerants.com.
“The goal of Walgreens was to have a net-zero, self-sustaining store,” Ali said. “That means you are generating energy from solar, wind and geothermal, and that energy is used to power the rack. With the CO2 system, we strive to operate it in an energy efficient manner.”
The typical energy consumption of a standard Walgreens store is about 780kWh per day. In comparison, on June 1, 2025, the Evanston store used around 269kWh of energy, 94% of which was supplied by its onsite energy sources, he reported. The energy savings are primarily attributed to the high operating efficiency of the CO2 rack, which results from lower gas cooler pressures achieved through the use of geothermal wells.
The integrated CO2 system has been operational since August 2024, with Zero Zone continuing performance evaluations to assess year-round energy use.
This project is one of more than 500 transcritical CO2 installations that Zero Zone has completed across the U.S. to date, Ali added.
System upgrade
Originally opened in 2013, the Evanston store was Walgreens’ first location to integrate solar, wind and geothermal energy. After encountering issues with its original refrigeration system, Walgreens upgraded in 2024 by partnering with Zero Zone, Copeland and Climate Pros to install a next-generation natural refrigerant-based system.
The Genesys CO2 Transcritical System supports:
- 33TR (166kW) of space cooling
- 60TR (211kW) of space heating and hot water
- 2TR (7kW) for medium-temperature refrigeration
- 2TR for low-temperature freezer loads
The system interacts with several technologies to optimize performance:
- A geothermal loop circulates 20% propylene glycol, functioning as both a heat source and heat sink depending on seasonal demand.
- A glycol chiller loop and heat exchanger connect to the CO2 rack to support cooling.
- A buffer tank helps balance thermal supply and demand.
According to Ali, the Genesys rack was selected for its performance, compact footprint, energy efficiency and system flexibility.
Given the system’s complexity, Copeland provided the control solutions, working closely with Zero Zone. “The controls are the heart of the system,” said Ali. “Without control, the systems cannot work. That has gone very smoothly so far.”
Stakeholder education
The store serves not only as a retail hub but as an educational showcase for sustainable refrigeration. The CO2 system is visible through a second-floor window, accompanied by informational signage explaining the technologies and their environmental benefits. Zero Zone has been working with Walgreens and contractors to provide the appropriate training. Since 2022, more than 500 technicians have become certified on Zero Zone CO2 equipment.
“Both Walgreens and Zero Zone believe in the importance of natural refrigeration education and have taken actions to continue spreading awareness of the impact refrigeration has,” Ali said.
“Both Walgreens and Zero Zone believe in the importance of natural refrigeration education and have taken actions to continue spreading awareness of the impact refrigeration has.”
Masood Ali, Global Refrigeration Manager at Zero Zone
