CO2 as a refrigerant has been a part of the refrigeration landscape for close to a decade. From early efforts combining it with ammonia in cascade systems for industrial plants to cascade and other approaches with hydrofluorocarbon (HFC) refrigerants in supermarkets, ammonia has established itself in the HVACR landscape.
The most anticipated next step was running CO2 as a stand-alone refrigerant in a system, which is being done in Europe in more and larger applications. This approach finally crossed the Atlantic and made a high-profile debut just a few months ago in Brooklyn, New York. And it continues to gain more and more attention in the states in refrigeration applications. Most recently, CO2 was showcased as a hot topic at the Food Marketing Institute Expo in Chicago.
This Refrigeration Zone story takes a look at a few recent developments, beginning with the Brooklyn application.
During a press briefing hosted by Danfoss earlier this year at the AHR Expo in New York City, Mike Ellinger, director of global maintenance and refrigeration for Whole Foods, talked about the transcritical CO2 store across the East River.
“Whole Foods Market is committed to reducing its environmental impact and supporting the health of its customers and team members, not only through the products it sells, but in how it designs, builds, and operates its stores,” he said. “We practice and advance environmental stewardship.”
He noted 11 existing Whole Foods stores with various types of CO2 systems including the 56,000-square-foot store in Brooklyn, which uses a booster CO2 system with subcritical compressors on low temperature and transcritical on the medium-temperature side. The Danfoss collaboration included variable-frequency drives (VFDs), rack control, system control, case controls, pressure independent control valves, solenoid valves, and heat exchangers.
He said challenges included a “higher initial system cost compared to a DX system, navigating permit requirements, lack of language in codes, and unexpected costs due to regulatory modifications.” This relates to an ongoing issue regarding CO2 as many of the technological advances are ahead of municipal code modifications.
Ellinger said Whole Foods will share a one-year report regarding the CO2 system performance, anticipated in early 2015.
At this point, he described one victory as bringing online “the first synthetic refrigerant-free store in the USA, with zero ozone depletion and low global warming potential.” He noted refrigeration is contributing to “an expected whole-building-design energy savings greater than 60 percent above the ASHRAE 90.1-2007 baseline.” He added the store is GreenChill Platinum- and LEED Platinum-certified, the highest certification levels available in both programs.
CO2 transcritical has had firmer standing for longer in Europe. The Sainsbury supermarket chain reported it was testing an Epta ECP2 small CO2 system in one of its stores in the U.K. CO2 is used in all of the convenience store’s refrigerated cases. In addition, the store was using 42 solar panels to generate electricity and double glazing for its LED lighting.
The innovations were part of what Sainsbury said was an effort to make the store “the greenest convenience store in the U.K.”
Carel is reporting on a transcritical CO2 store in Belluno, Italy. The refrigeration system uses CO2 for medium- and low-temperature applications in a direct-expansion approach. An Epta control manages the system.
In the broadest sense, Carel explained the transcritical cycle this way: “In the cycle that is defined as transcritical, the normal chiller condensation cycles using the most common refrigerants are replaced by a heat exchange between the refrigerant, which is at a higher pressure than the critical one and the cooling fluid. In transcritical operation, there is no phase change from gas to liquid — only the decreasing of the temperature of a gas that is gradually denser. The maximum operating pressure is no longer linked to the condensation temperature, but is instead controlled by means of the assembly comprised of a valve and a liquid receiver.”
Resource Data Management designed what many recognize as New Zealand’s first transcritical CO2 refrigeration supermarket last fall in Auckland. Company reps said a monitoring system was designed to optimize energy consumption to the mechanical system.
This was a retrofit project implemented in response to new legislation in the country designed to encourage switching away from HFCs. The old system was pulled out and replaced by two CO2 packs. One was a booster system providing cooling to the low-temperature side and some medium-temperature equipment. The remainder of the medium-temperature load is cooled by a second CO2 pack. The system is linked to a heat recovery system that draws energy from both packs to heat the retail area and provide hot water.
Officials also said the store will serve as an onsite training site for technicians interested in working with CO2.
In addition to the industry’s awareness of CO2 training, the need for products specific to that refrigerant are needed.
Drawing attention to that factor is Westermeyer Industries of Bluffs, Illinois. It issued a press release announcing a product line expansion to incorporate “a full line of code-approved high-pressure components supporting operating pressures of transcritical CO2 systems.”
The product line includes oil separators, oil reservoirs, accumulators, and receivers.
“We are constantly striving to meet our customers’ needs and fulfill the needs of the refrigeration industry,” said company founder, Gary Westermeyer. “Our transcritical products help our customers provide an environmentally friendly system to the end user, thereby meeting green initiatives.”
Publication date: 8/4/2014