In “Hotlanta,” ambient temperatures routinely rise above 87.8F. That’s the critical point temperature for the emerging natural refrigerant CO2 (R-744). When the temperature outside approaches this point, CO2-based commercial refrigeration systems begin to experience declining efficiencies. That’s why CO2-based refrigeration architectures are more common in cooler climates. And why CO2 transcritical booster systems — which rely entirely on CO2 — are not considered an obvious solution in places like Atlanta.
However, with increasing regulations prompting a shift toward sustainable alternative refrigerants, retailers are looking more closely at CO2 transcritical booster systems to anchor their refrigeration operations, even in warmer climates. With more than 200 U.S. locations, Sprouts Farmers Market, a healthy grocery chain that offers fresh, natural and organic foods, is among the first retailers in North America to do just that. They opened their first store in suburban Atlanta in July 2014, and when they did, they set out to prove CO2 transcritical booster systems aren’t only for cool climates. But Sprouts had clear business objectives for their CO2 pilot program, as well. Their senior leadership wanted to reduce the company’s carbon footprint and mitigate regulatory compliance concerns. The forward-thinking grocery chain wanted to push the envelope and establish a sustainable refrigeration alternative in their new fleet of southern stores.Going Green and Keeping It Fresh When you’re a grocery chain focusing on selling fresh foods, fresh is the fundamental ingredient. That means your refrigeration system design has to be—above all else—reliable. Like many food retailers, Sprouts has historically employed more traditional refrigeration systems based on common hydrofluorocarbon (HFC) refrigerants. These HFC systems operate with what’s traditionally seen as acceptable temperatures and pressures.
Emerson Climate Technologies, Hillphoenix and Sprouts all shared the same goal: show the industry it’s possible to operate an efficient refrigeration system in higher ambient temperatures using CO2 exclusively. CO2’s low critical point temperature and high operating pressure (around 1,500 psig) are characteristically not found in traditional HFC-based refrigeration. These are the primary reasons for the reluctance to move toward CO2. But, with advances in system technology and architecture, CO2 can be a game changer for retailers seeking to improve energy efficiencies, achieve sustainability targets and cross the finish line on regulatory compliance. Changing their refrigeration philosophy and moving to a CO2 transcritical system architecture was a giant step for Sprouts, especially for this store in the hot, humid climate of Atlanta. To pull this off, they turned to OEM partner Hillphoenix, whom the company partnered with to earn an EPA GreenChill platinum certification in 2011. And Hillphoenix, seeing the challenge presented by installing a CO2 transcritical booster system in a warm climate, turned to Emerson Climate Technologies.Transcritical Technology in Action Emerson Climate Technologies, Hillphoenix and Sprouts all shared the same goal: show the industry it’s possible to operate an efficient refrigeration system in higher ambient temperatures using CO2 exclusively. A key enabling feature of the CO2 transcritical booster system is an adiabatic condenser, which was designed to operate in high ambient temperatures. A key enabling feature of the CO2 transcritical booster system is an adiabatic condenser, which was designed to operate in high ambient temperatures. Adiabatic condenser cooling is the process of spraying water into the air supply of an air-cooled condenser to pre-cool the air and improve refrigeration efficiency. The goal of this condenser technology is to keep the CO2 below its critical point, thus maximizing system efficiencies. Hillphoenix’s rack refrigeration system featured four Copeland semi-hermetic transcritical CO2 compressors and three Copeland Scroll ZO compressors. Both models were designed for CO2’s high-pressure requirements and benefit from its thermal properties. Emerson’s E2 Facility Management System was installed to oversee the CO2 transcritical booster system, manage nearly 50 electronic case control units and optimize the facility’s overall energy management profile. Emerson sources report the E2 system helps improve performance in multiple ways: 1) Controls the variable speed of the fans on the adiabatic condenser in response to operating conditions 2) Optimizes compressor coefficient of performance by regulating system discharge pressures via Emerson’s high-pressure CO2 controller 3) Provides complete oil management control of all CO2 refrigeration compressors 4) Communicates with and captures information from individual case control units 5) Provides complete control of building HVAC and refrigeration systems, and supports the retailer’s energy and maintenance reduction strategies. The E2 system also allows Sprouts operators to run diagnostics, monitor the system remotely through Emerson’s ProAct Service Center and, if necessary, shut down the system components before failure. The condenser manages both low- and medium-temperature refrigeration requirements on the same system using only CO2 as the refrigerant, another unique aspect to the transcritical booster system. Running both requirements from the same condenser enhances the efficiency of the system across the store.Easing Concerns CO2 transcritical booster systems have been used in Europe for nearly a decade. Adoption by the U.S. refrigeration industry has been slower due to a general apprehension about new (and, to many, unknown) technology. It’s understandable why stateside end users are hesitant to switch to CO2 transcritical booster systems. Concerns over operating pressures, maintenance levels and energy have prompted careful and steady evaluations to understand the true cost of ownership for their enterprises. Emerson technology helped ease those concerns for Sprouts. Their Atlanta-area store is operating efficiently and effectively on the transcritical system.