Leak Busters

MICHAEL GARRY

Since October 2008, the GreenChill Advanced Refrigeration Partnership, a program run by the U.S. Environmental Protection Agency for food retailers and refrigeration vendors, has presented only two stores with its platinum-level store certification award, the highest award the program bestows. The program has also given 11 gold-level and 20 silver-level certifications in that time.

To earn the platinum certification, a store must use a very small amount of refrigerant charge (no more than 0.5 pounds of refrigerant per 1,000 BTU per hour) and have an annual refrigerant emissions rate of no more than 5%. Those miniscule numbers would distinguish a store both for environmental friendliness (toward the ozone layer and climate change) and cost savings; by contrast, the average supermarket's refrigeration system leaks about 25% of its refrigerant charge each year, according to the EPA.

The two stores that received the platinum certification are a Star Market in Chestnut Hill, Mass., and a Price Chopper in Colonie, N.Y., which was recertified last month. (The Colonie store originally received a gold certification in June 2009.) It turns out that although the stores have different owners (Supervalu and Golub Corp., respectively), they both use the same refrigeration systems — a secondary loop design for medium-temperature and low-temperature cases. The systems are provided by Hill Phoenix, Conyers, Ga.

Secondary loop systems are noted for reducing the amount of traditional refrigerant used — and the potential for leaks — by confining the refrigerant to the machine room and using a secondary fluid to cool the cases in the store. But the Star Market and Price Chopper systems take that concept further to reduce the refrigerant charge and annual leak percentage to industry-leading levels.

How do they do that? The most dramatic change takes place on the medium temperature side — responsible for cooling dairy, meat and other non-frozen foods; there, the secondary loop system employs a series of contiguous “compact chiller” modules instead of a traditional rack of parallel DX (direct expansion) compressors. The chillers cool the secondary fluid — a water/propylene glycol mix — that flows out to the cases.

What makes each chiller unit unique is that it contains a single “multi-channel heat exchanger,” which combines a heat exchanger for cooling, condensing and liquid sub-cooling in one unit. Hill Phoenix licenses the heat exchanger from a Swedish company for these compact chillers, which are designed for the U.S. market, said Scott Martin, director, sustainable technologies for Hill Phoenix.

Other U.S. chains using compact chillers include Harris Teeter (in two stores) and Roche Bros. (in two stores), along with three independent operators in single stores, said Martin. Compact chillers have been used in European supermarkets for a number of years.

Each compact chiller module “is an independent chiller in and of itself,” explained Martin. This means that each unit has the components for a complete refrigeration cycle — compressor, condenser and evaporator — and is pre-charged by Hill Phoenix, eliminating all refrigeration piping in the control room. When the chillers are grouped together, the effect is similar to lining up a series of home refrigerators. The result is a dramatic reduction in the amount of refrigeration charge.

“Compact chillers represent an almost completely new approach to supermarket refrigeration,” said Keilly Witman, communication specialist, EPA's Office of Atmospheric Programs, and manager of the GreenChill program. “Instead of one huge system with large amounts of refrigerant, you have many smaller units lined up next to each other.”

95% CHARGE REDUCTION

At Price Chopper's year-old, 69,000-square-foot Colonie store, 12 compact chiller modules (two stacks of six) require only 8.5 pounds of R-404A refrigerant in each module, for a total of just 102 pounds, 95% less than a traditional DX system, said Mark Hankle, senior mechanical engineer for Price Chopper, who described the compact chiller system last fall at the Food Marketing Institute Energy & Technical Services Conference in Indian Wells, Calif. (With an energy load of 875,000 BTUs, the GreenChill ratio for the chillers is 0.12 pounds per 1,000 BTUs.)

The most that could leak out of any compact chiller at Price Chopper is a trifling 8.5 pounds, compared with several hundred pounds in a traditional compressor, and a few hundred pounds in a traditional secondary loop system. According to Witman, the stores with compact chillers that are starting to renew their GreenChill certifications (platinum and gold) are not reporting any leaks in the systems at all.

On the low-temperature side — responsible for chilling frozen cases — the Price Chopper Colonie store uses six modules (not compact chillers) in concert with liquid carbon dioxide that circulates through the cases. Each module contained 30 pounds of R-404A refrigerant for a total of 180 pounds; with a load of 363,000 BTUs, the GreenChill ratio is 0.5 pounds per 1,000 BTUs.

Thus the refrigerant charge for the entire Colonie store is just 282 pounds — a far cry from the 4,000-pound charge that can be used in a traditional DX system. “I was trying to get the lowest refrigerant charge in the system that I could,” so that the most that could leak from any section would be under 50 pounds, said Hankle. Being under 50 pounds per section would keep Price Chopper below EPA record-keeping requirements should they ever be applied to HFC refrigerants, noted John Gallaher, director of marketing and business development for Hill Phoenix.

The platinum-certified, 53,500-square-foot Star Market store has also reported markedly low refrigerant levels. According to an audio transcript posted on the GreenChill website of the platinum-award ceremony held at the store in September of last year, Dave Smith, systems sales manager for Hill Phoenix, said the store used a total of 264 pounds of refrigerant. The store's compact chiller system consisted of 14 units, each with 11 pounds of refrigerant, he said. The low-temperature modules each held 20 pounds. The maximum leak potential of the store is just 2%, said Holly Angell, director of the engineering department at Supervalu that designed the systems in the Star Market, according to the transcript. “The very most we could ever leak is 20 pounds and we don't expect that to happen at all,” she said.

The reduction of charge and leak rates at the Price Chopper and Star Market stores was so notable that it prompted the GreenChill program to create the platinum-level certification, said Witman. “They turned out to be so much better than the gold level, it almost seemed a shame to give them just gold.” Besides meeting the stringent charge and leak requirements achieved by those stores, the only other way to earn platinum certification would be to use a refrigerant with less than a 150 global warming potential — essentially a natural refrigerant — which has not been done yet in the U.S.

In addition to using a small amount of refrigerant, the compact chillers, located in an enclosure on the roof of the Colonie store, offer other advantages, said Hankle. For example, their installation “was very smooth,” with Hill Phoenix training the chain's technicians and contractors, he told SN in a recent interview. Maintenance has also been “very favorable to date,” with no major issues. impacting system performance. Price Chopper is able to “slide out” a chiller module that needs repair and send it to Hill Phoenix, while a substitute is used. This maintenance scheme means that “you don't have to waste time waiting for a service technician to arrive and repair the leaks while refrigerant is continuing to leak,” said Witman. (The low-temperature modules can't be removed in this way.)

HIGHER COST

The disadvantage to the compact chiller system is that its up-front cost is 20% to 40% higher than that of a traditional DX system, said Hankle. The system's steeper cost is due to its more advanced heat exchanger as well as the additional pumps for circulating condensing fluid, said Gallaher. Price Chopper is still evaluating whether the savings in installation, maintenance and charge reduction compensate for the up-front cost premium of the chillers; the chain is also still assessing the compact chiller's energy requirements compared with a standard system. Until the overall value of the compact chillers is determined, Price Chopper is not installing them in any other stores, Hankle said.

Including the Colonie store, Price Chopper has five supermarkets with secondary systems of varying kinds, “with more to come,” said Hankle. The other systems were found to use the same amount of energy as standard DX systems but offer a maintenance savings.