On Nov. 27, 2007, the U.S. Environmental Protection Agency held an unusual event at its headquarters in Washington near the White House: the official launch of the GreenChill Advanced Refrigeration Partnership with the supermarket industry.
What made this event unusual? For many years, the EPA — in particular its Stratospheric Protection Division — has been policing food retailers' refrigeration practices in order to limit the escape of ozone-depleting refrigerants into the atmosphere. This oversight, which includes a 35% annual leak-rate cap on food retailers, has resulted in penalties and other costs that have strained the supermarket industry's relationship with the EPA.
Yet at the GreenChill launch event, several major food retailers — Food Lion, Hannaford Bros., Giant Eagle, Whole Foods Market, Harris Teeter and Publix Super Markets — put aside any anti-EPA feelings to form a partnership with the agency intended to develop more environmentally friendly and cost-effective refrigeration practices and technology. (All of these retailers except for Harris Teeter had previously joined GreenChill earlier in 2007 before its official launch.) The EPA is urging other retailers to follow suit.
Julius Banks, the EPA's acting branch chief, Alternatives and Emissions Reduction Branch, told SN in early November — and repeated at the GreenChill launch — that the willingness of the founding GreenChill retailers to work with the EPA and each other was “something I would not have thought possible when I started attending the FMI Energy Conference five years ago.”
The GreenChill program also includes refrigeration equipment manufacturers Hill Phoenix, Kysor/Warren and Hussmann, as well as refrigerant manufacturers Honeywell, Arkema, Dow Chemical and INEOS Fluor.
Through GreenChill, the EPA aims to work with retailers on reducing leaks from refrigeration equipment of ozone-depleting hydrochlorofluorocarbon (HCFC) refrigerants, notably R-22, as well as newer hydrofluorocarbon (HFC) refrigerants that are not ozone-depleting but still contribute to global warming. GreenChill is also intended to help retailers phase out use of R-22 in favor of HFCs. Production and importation of R-22 for new equipment will cease in 2010, and all R-22 production and importation will terminate in 2020.
But perhaps of greater long-term consequence, the retailers in GreenChill are for the most part investing in advanced refrigeration technology, if only on a test basis (though that is not a program requirement).
Advanced refrigeration technology includes secondary-loop systems and distributed systems that represent a departure from the conventional direct expansion (DX) refrigeration process. These systems are designed to achieve the GreenChill program's overall goals of reducing refrigerant usage and leaks and transitioning to more environmentally friendly chemicals.
Food Lion, Salisbury, N.C., the first food retailer to publicly commit to the GreenChill program, in January 2007, has been testing a medium-temperature secondary-loop system at a store in Dinwiddie, Va., for two years and a low-temperature secondary-loop system at a store in Montpelier, Va., for more than a year. In April, the chain plans to open a store in Portsmouth, Va., where it will test both types of secondary-loop systems.
Cold-Weather System
Meanwhile, Hannaford Bros., Scarborough, Maine — like Food Lion a division of the Delhaize Group — has been quietly testing its own advanced refrigeration system for the past year as part of its participation in the GreenChill program. While following a DX design, Hannaford's system, developed by its own in-house engineering team, is different from anything else in the U.S. market, said Harrison Horning, Hannaford's director of facilities and energy. The system is tailored to meet the needs of stores in a cold-weather climate.
Hannaford's advanced refrigeration system, which uses a non-ozone-depleting refrigerant (R-507a), has been running in two remodeled stores; one unit of the system has been operating for a year in one store, and two units have been running for six months in the other. In addition, Hannaford will deploy the system in 10 other stores (some new, some remodels), including four by the end of 2008. The first new store with the advanced system is expected to open in December; all of the refrigeration in that store will be generated by four units of the advanced system.
In the first two stores, the advanced system has been “reliable and working well,” said Horning. The system is also generating more heat for use in the store than a conventional system. Though Hannaford has used heat reclamation extensively, the advanced system allows the chain to provide “up to 100% of a store's heating needs,” he said. Compared to a conventional system, the advanced system uses more electric energy, but the additional heat reclaimed translates into lower fuel costs and a net energy savings.
Hannaford's advanced system is like a conventional DX system in that both use continuous-loop compression and condensation of standard refrigerant gas to generate heat, and then the expansion of refrigerant liquid to generate cold. Hannaford's system differs, however, in the way it condenses refrigerant gas and in its use of less high-pressure refrigerant piping and of narrower-diameter liquid refrigerant piping, thereby reducing the amount of refrigerant required. It is also designed to reduce the number of leaks that occur.
In a conventional system, heat is generated and reclaimed via the condenser, where refrigerant gas condenses to liquid. That is true in the advanced system, except that its condenser uses a different technology — a “plate heat exchanger” — and the heat is conducted to the store via a water-glycol loop. When heat is not needed, it is rejected from rooftop equipment.
Horning acknowledged that, compared to a conventional system, the advanced system incurs added costs for the plate heat exchanger and pump, as well as the HVAC elements needed to capture the reclaimed heat. “The incremental cost varies by project, and we don't have good numbers yet,” he said.
Shrinking the Charge
Hannaford has not yet measured the refrigerant- and leak-saving attributes that will distinguish this system from others. But the chain expects the advanced system to reduce refrigerant charge (quantity) by 50% compared to a conventional DX system, Horning said. With the high global warming effects of even non-ozone-depleting refrigerants, “the only way to feel good is to shrink the charge — that's where we want to head,” he said.
In its first new store, he added, the chain expects at least a 75% reduction in refrigerant leaks. The advanced system reduces refrigeration leaks partly by being able to more easily identify when leaks have occurred. To accomplish this, Hannaford has designed the system with less piping so that the amount of condensed liquid refrigerant collected in the “receiver” is more stable than in a conventional DX system. When the amount of refrigerant in the receiver drops, a monitor sets off an alarm “indicating a probable leak,” said Horning.
When leaks occur, it is easier to find and fix them, because the system contains much less high-pressure refrigerant piping than a conventional system. That piping — and the condenser — are located near the compressor rack in the machine room. The piping does not snake up to the roof, as in a conventional system. “We go from the compressor to the receiver in about 5 feet of pipe,” said Horning. However, the leak points in the liquid piping that feeds display cases “have not been rectified yet.”
Using less high-pressure piping allows Hannaford to also use less refrigerant, because “the amount of refrigerant required to fill the system is reduced substantially,” said Horning. About 80% of the refrigerant reduction occurs here.
The advanced system uses smaller-diameter piping to move liquid refrigerant to the evaporators in the medium- and low-temperature cases and walk-in coolers in the store, where the evaporation to a gas produces the cooling effect (not unlike perspiration evaporating from skin). The narrower piping again reduces the amount of refrigerant used.
But in order to use narrower piping, the system needs to employ what's called “subcooling,“ which increases the efficiency and cooling capacity of the system. In Hannaford's system, the Copeland scroll compressor used has a built-in subcooling mechanism that provides subcooling whenever the compressor is running.
To further reduce the amount of refrigerant used in the system, Hannaford is studying whether it can incorporate secondary-loop refrigeration technology, Horning said.
Commenting on Hannaford's system, Ron Vogl, technical service engineer at Honeywell, Morristown, N.J., said keeping refrigeration in the compressor room and away from the roof, with less high-pressure piping and reducing charge, is a “good approach.” He also commended the effort to maximize heat reclamation in a northern climate.
But Vogl noted that optimizing a supermarket refrigeration system will cost “more money up front.”
