Use of CO₂ as a primary or sole refrigerant in a refrigeration system has become a common trend in Europe and is gaining favor in the U.S. CO₂ is primarily used in cascade systems that include ammonia, in booster systems in supermarkets, and as a stand-alone refrigerant for transcritical-configured systems.

Advanced CO₂ refrigerating systems that incorporate partially flooded evaporators are also being developed. Here is a look at some of these refrigerants in use in the U.S. and Europe.

Large-scale CO₂

The refrigeration system used within a 300,000-square-foot Caputo’s Fresh Market building in Carol Stream, Illinois, uses Hillphoenix’s Advansor™ line, which uses an environmentally sustainable CO₂ refrigerant, rather than a hydrofluorocarbon (HFC) refrigerant typically found in traditional commercial refrigeration systems.

Robertino Presta, CEO, Caputo, said the CO₂ system was more expensive on the front end than an HFC system, but he expects to recoup the investment through lower refrigerant and energy costs. Plus, he said he now doesn’t have to worry about the potential of future HFC regulations. (At the time of this writing in late-December 2014, the U.S. Environmental Protection Agency [EPA] was proposing a ban on the use of certain high-GWP [global warming potential] HFCs on equipment manufactured beginning in 2016; and, globally, there continues to be discussions among many countries to regulate HFC use under terms of the Montreal Protocol.)

Caputo’s crew, which was most familiar with HFC-based systems, received training from Hillphoenix representatives, helping them learn how to service and maintain the CO₂ system.

“Hillphoenix’s Advansor system has helped me future-proof my business,” Presta said. “On top of that, installing CO₂ was the right thing to do.”

Hillphoenix said its system offers numerous benefits, including the use of a natural and inexpensive refrigerant, sustainability, low-GWP performance, energy efficiency, quiet operation, and more.

“Hillphoenix helped us create a functional and beautiful space that achieves our goals of driving business efficiency and turning our customers’ shopping trips into events,” Presta said.

Smaller-scale CO₂

Frigo-Consulting Ltd., a Bern, Switzerland-based engineering and contracting company, facilitated the remodeling of a Migros supermarket store in the Mythen Shopping Center in Ibach, Switzerland. The supermarket’s 32,000-square-foot sales area was retrofitted with what Frigo called an advanced CO₂ refrigerating system. The system was installed on-site to cool 170 medium- and low-temperature cabinets and cold rooms. Two identical CO₂ booster units provide a total of 250 kW of refrigerating capacity.

Those involved in the project contend the system brought forth a significant increase in efficiency.

According to Frigo, both of the CO₂ refrigerating units are designed so that all medium- and low-temperature evaporators can be operated partially flooded. Thus, the refrigerant is still partly liquid at the outlet of the evaporators. This increases the heat exchange efficiency of the evaporators and the product temperature can be better guaranteed despite the higher evaporation temperatures.

There is a high evaporation temperature that results in a saving of electrical energy aided by a boost in efficiency reached by five ejectors per CO₂ refrigerating unit. Driven by the pressure difference in the system between high and medium pressure, the ejectors convey liquid or gaseous refrigerant. The liquid refrigerant in the medium-temperature suction-line receiver is returned to the medium-pressure receiver and brought back to the partially flooded evaporators. Frigo said the gaseous refrigerant is also pre-compressed by the ejectors to the medium-pressure receiver. It’s further compressed to high pressure by the parallel compressors. The five ejectors allow the system to react to all operating conditions and load situations and ensure the highest possible operational reliability, the company said.

The combination of ejectors and parallel compressors allows for the recovery of the energy released during expansion and the reduction of the internal throttling losses.

The CO₂ refrigerating systems are cooled in the summer months by groundwater, which allows for the reduction of the the refrigerating unit’s high pressure and causes them to operate more efficiently, the company said.

Publication date: 3/2/2015

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