Transcritical CO2 (R744) refrigeration has proven to be a versatile application that can be employed in a number of sectors, including supermarkets, industrial sites and ice rinks.

As contractors, Minneapolis-based South-Town Refrigeration & Mechanical and its sister company SCR (St. Cloud Refrigeration), which cover the Upper Midwest of the U.S., have been equally versatile, installing transcritical systems in all three sectors in Minnesota over the past two years.

“Now that we have systems in different settings, we have a good test of everything,” said Ryan Welty, vice president of sales and operations for both companies, which are co-owned by Welty’s father Pat and Mike Fitch. Fitch’s father, Don, started SCR, a non-union shop, in 1957, and the families purchased unionized South-Town in 2009.

Importantly, with a few years of experience working on CO2 systems, Welty’s service technicians are “not scared” of them anymore,” he said. “And manufacturers have a good base as well.”

The first CO2 project, handled two years ago by South-Town, was for a new innovation/technology center in Downtown Minneapolis where Jack Link’s Beef Jerky tests new products. An Advansor transcritical CO2 system (from Hillphoenix), is used in a 10,000-ftprocessing area along with Colmac custom DX evaporator coils and Micro Thermo Controls (from Sporlan). The system delivers a low-temperature capacity of 36.4K BTUH and a medium-temperature capacity of 575.5K BTUH.

The transcritical system leverages heat reclaim to create hot water used to preheat the water required for the wash down of the processing area.

A unique aspect of the Jack Link’s project is that the CO2 discharge gas is cooled in a heat exchanger by chilled (40°F-50°F) water provided via underground pipes by Clearway Energy’s Energy Center; the Energy Center supports cooling and heating in 100 buildings in downtown Minneapolis.

The cooled water prevents the CO2 system from ever entering “transcritical mode,” in which high ambient temperatures prevent the gas from condensing, said Welty, adding, “It’s the perfect application for CO2.”

“Now that we have systems in different settings, we have a good test of everything.”

Ryan Welty, South-Town Refrigeration & Mechanical/SCR

Supermarkets are Welty’s biggest area of focus. Last year, South-Town installed its third supermarket CO2 system, a Advansor transcritical model with an adiabatic condenser at a new Lunds & Byerlys store in White Bear Lake, Minn., outside of Minneapolis. It is the first CO2 system in the U.S. to use RDM (Resource Data Management) controls, said Welty. (RDM controls have also been used in European stores.)

“RDM flew in people from Europe to make sure it was set up correctly,” he said, noting that the unit had to be adjusted from the metric to U.S. measurements. Lunds & Byerlys requested the RDM controls because the 27-store upscale chain uses them in its HFC systems.

The White Bear Lake store’s transcritical system delivers a low-temperature capacity of 205.5K BTUH (-16°F) and a medium-temperature capacity of 873.1K BTUH (19°F).

The CO2 system has consumed less energy than an R407A system at a comparable nearby store, noted Welty.  “They beat it every month,” including warm periods in late summer-early fall, he said, though he could not provide consumption data.

Welty acknowledged a first-cost premium for CO2 equipment, but said that installation costs were no higher than traditional systems. He attributed higher first costs to the greater use of electronic case controls.

South-Town has also installed CO2 secondary systems at Target (for which it has also installed a transcritical CO2 system) and Walmart stores, Welty said.

South-Town Refrigeration is also working with self-contained R290 cases at retailers like Target though he doesn’t see a major move to R290 until higher charge limits are adopted in the U.S. (The IEC has raised the global hydrocarbon charge-limit standard for stand-alone cases to 500 g.)

Last year, SCR installed the first transcritical CO2 system in an ice rink in the “lower-48” part of the U.S. (CO2 ice rinks were previously deployed in Anchorage, Alaska.) The 170-TR chiller system, using glycol as a secondary fluid, serves an existing ice rink (replacing an R22 system) and a new rink at the St. Michael-Albertville Arena, Albertville, Minn. The system also employs a Guenter Cooling Tower and Micro Thermo Controls.

Welty is currently installing an ammonia refrigeration system for an ice rink, he said.

The biggest challenge Welty faced in his initial CO2 projects was getting over the “fear factor” associated with new technology. “But we decided we were going to do this, and find good partners willing to take a chance with us,” he said.

Another hurdle was supporting stores in remote regions of the Upper Midwest where there are scant supplies of refrigerant-grade CO2. In one case a store in North Dakota had to purge its CO2, and the closest supply was an eight-hour drive away. “We got it to them but they lost product,” said Welty, who agreed that remote stores should invest in having extra CO2 supplies on hand.

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