U.S.-based manufacturers Copeland and Zero Zone have installed CO2 (R744) refrigeration systems for a wide variety of small format retailers, including the convenience store Kwik Trip, Walgreens pharmacy and the grocery stores of ALDI US and Natural Grocers.
Details of system designs and installations at five new stores in various U.S locations were presented at the Food Industry Association (FMI) Energy and Store Development Conference by Brent Cheshire, Manager of End User Services, Cold Chain at Copeland and Dan O’Brien, Zero Zone President. The event was held in Baltimore, Maryland, October 2‒4.
O’Brien defined small format retailers as those with a store footprint of less than 25,000ft2 (2,323m2) requiring roughly 30TR (105.5kW) capacity. “We can apply [CO2] in basically everything and anything; it’s not just for the big box stores anymore,” he said, indicating that costs for CO2 systems have come down in the last few years.
Most of the time, the smaller store design seeks to maximize the energy efficiency of the CO2 rack by using as low as possible head pressure, O’Brien indicated. “However, there are applications for heat reclaim, especially as the electrification of heating becomes more predominant in our industry.”
“Depending on what we are trying to accomplish, we can drive the head pressure up and use the heat from the CO2 system for hot water, space heating, dehumidification and more,” he added.
All five locations used Copeland CO2 supervisory control. “We’ve got so much more data on the CO2 systems than ever before,” Cheshire said. “Bringing the whole rack solution into one screen reduces the complexity and makes the service technician’s job easier to understand what is happening across the entire system.”
Three different system architectures were used in the various formats. The two Natural Grocers stores, both located in Denver, Colorado, used indoor parallel systems. The ALDI store in Joplin, Missouri, and the Kwik Trip C-store in Dayton, Minnesota, used an outdoor parallel system. The Walgreens store in Islandia, New York, used Zero Zone’s Edge XT outdoor distributed system.
“We can apply [CO2] in basically everything and anything; it’s not just for the big box stores anymore.”
Dan O’Brien, Zero Zone President
Natural Grocers
According to O’Brien, Natural Grocers ‒ with 167 stores in 21 states ‒ had “traditionally” been using racks with R404a or R448a and moving through refrigerants based on changing regulations. “Their reason for moving forward with a CO2 system was to be ready for what happens next,” he noted.
With Denver’s hot, arid climate, as shown by a maximum dry bulb temperature of 104°F (40°C) and a maximum wet bulb temperature of 69.5°F (20.8°C), “they have a good ability to stay in the subcritical CO2 operating zone,” O’Brien said.
The Stapleton and Brighton stores used the same 120bar (1,740psi) high-pressure and 45bar (653psi) low-pressure design in an indoor rack. The racks consist of three Copeland 4MTLS transcritical CO2 semi-hermetic compressors for medium-temperature (MT) loads and two Copeland subcritical CO2 scroll compressors ‒ ZO and ZOD ‒ for low-temperature (LT) loads.
For efficiency, the LT discharge feeds the MT suction, with the MT discharge cooled by a remote adiabatic gas cooler. “The LT scroll has provided nice stable capacity control on the LT side, and a variable speed compressor with variable frequency drive [VFD] on the lead MT compressor gives us capacity control in MT,” O’Brien said.
“We used a single fan adiabatic gas cooler due to the arid climate,” O’Brien said, noting that the single fan was the one area causing the customer the most concern. The grocer has a third store in the planning stages on the west side of Denver. “We will be addressing that in the design of the next store.”
The biggest challenge for the Natural Grocers installations was the consecutive five days with ambient temperatures below -15°F (-26.1°C). “It was a struggle to keep everything under control at those temperatures, but we got through it with dial-in controls and working with the contractor,” O’Brien noted.
The lesson learned from these installations was the need for a “manual bypass valve around the high-pressure valve [HPV] to keep the rack running,” O’Brien said if the HPV goes out.
Natural Grocers also used a “charge saver system” with a generator-run small condensing unit hooked to a plate heat exchanger. “If there is an issue with the rack or a power outage, the charge saver keeps the CO2 cool and in the system,” Cheshire said.
Walgreens
Much like a restaurant, Walgreens ‒ with 8,793 stores in 50 states ‒ only needed a single box cooler and freezer for its store. Zero Zone used its roof-mounted Edge DX platform, housing two independent circuits ‒ MT and LT. A remote air-cooled gas cooler met the mixed humid climate of Long Island, New York, at the Islandia location.
“We designed this one for 120bar high side and 90bar [1,305psi] low side,” O’Brien said. “With the evaporators and boxes rated for 90bar, we don’t have a charge saver since there is no risk of CO2 loss.”
Copeland provided leak detection and all CO2 controls, including the case and walk-in, high-pressure and supervisory controls.
According to O’Brien, during the startup, there was a VFD challenge to manage. “[However], it has been working for about six weeks and running very well.”
Kwik Trip
The Wisconsin-based C-store Kwik Trip operates 853 stores in five states, but the company is “moving into more states and growing every day,” O’Brien noted. The store requires refrigeration for walk-in coolers and freezers, beer caves, ice machines, slushy machines and refrigerated cases.
Although most convenience stores do not use refrigeration racks, according to O’Brien, Kwik Trip has used the architecture for over ten years, with R448a racks for the last five years.
This is Kwik Trip’s second store to use CO2 refrigeration. Its first store in La Crosse, Wisconsin, opened in June 2022 with a transcritical CO2 rack from Hillphoenix.
The Dayton, Minnesota, store has close to the same design as the Denver Natural Grocers stores but is configured in an outdoor parallel system mounted on the roof with a remote air-cooled gas cooler instead of an adiabatic. “We are in a cold area of Minneapolis, and we didn’t feel like we needed to go adiabatic,” O’Brien indicated.
The Dayton store has been in operation since March, with a typical design seen in supermarket applications in the climate zone, Cheshire added.
Under its 2023 GreenChill Store Certification Program, the Environmental Protection Agency (EPA) recognized Kwik Trip for having “the first convenience store to receive a GreenChill Certification” as part of the FMI conference.
According to Carl Klemp, Kwik Trip Senior HVAC/R Engineer ‒ in a presentation at the ATMOsphere (ATMO) America Summit 2023 ‒ the chain has committed, starting July 2023, to installing transcritical CO2 refrigeration in all of its new and remodeled stores.
ALDI US
The Illinois-based ALDI US ‒ with 2,312 stores in 39 states ‒ operates over 600 stores using transcritical CO2 refrigeration systems, earning the chain Store Certification Excellence at EPA’s 2023 GreenChill awards and 2023 ATMOsphere America’s Best in Sector/Retail award. O’Brien and Cheshire highlighted the system the pair felt “fortunate enough” to manufacture and install at the chain’s Joplin, Missouri, location.
With a design much like the Denver Natural Grocers and the Minnesota Kwik Trip with three MT compressors and two LT compressors, the roof-mounted system used a two-fan adiabatic gas cooler to handle the mixed humid climate.
This system also reclaims heat, providing hot water and comfort heating. The store has been operating extremely well since its initial startup in 2021, O’Brien indicated.
“All the applications provide real-time readouts, with each point fully customizable to the end user, OEM or the technician level,” Cheshire noted, with Copeland providing supervisory controls. “Seeing the historical operational data with its stability trends is like providing extra tools to the technicians.”
Lessons learned
According to O’Brien, the biggest lesson learned from these installations is to take the time to do the pre-start-up work, validating sensors, pressure transducers, wiring and other control points.
“Understanding the climate zone determines the best application for the gas cooler, whether it is adiabatic or air-cooled to get rid of the heat,” he added.
“CO2 is definitely here to stay and is going to be a big part of our industry going forward.”
Dan O’Brien, Zero Zone President
