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Advanced Refrigeration Technology

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Most of the 34,000 supermarkets in the United States use what is generally referred to as a "direct expansion (DX) refrigeration system" to chill their products. These systems typically use large charges of refrigerant, and they can have high leak rates, often leaking in excess of twenty percent of their charge per year. Nearly all supermarkets in the U.S. today use ozone-depleting hydrochlorofluorocarbon (HCFC) refrigerant, usually R-22, or a blend consisting entirely or primarily of hydrofluorocarbons (HFCs). HCFCs and the HFCs are also greenhouse gases. There are several options in refrigeration technology for supermarkets to reduce refrigerant charges and refrigerant emissions. Below is a general description of a traditional DX system and two of the most common advanced refrigeration technologies followed by technical information on Advanced Refrigeration Technologies.

Direct expansion system (traditional system)

Schematic of a Traditional, Direct Expansion SystemSupermarket refrigeration systems have traditionally been direct expansion (DX) systems (used in about 70 percent of the supermarket refrigeration market). These systems typically use refrigerants R-22, R-502 (a blend of R-22 and CFC-115), R-404A (a blend of HFCs), or R-507A (ablend of HFCs).

The average emission rate of DX systems is believed to be between 15 and 30 percent. Most of the emissions are due to leaks in the system, including leaks in the valves and compressors.

In a direct expansion (DX) system, the compressors are mounted together and share suction and discharge refrigeration lines that run throughout the store, feeding refrigerant to the cases and coolers. The compressors are located in a separate machine room, either in the back of the store or on its roof, to reduce noise and prevent customer access, while the condensers are usually air-cooled and hence are placed outside to reject heat. These multiple compressor racks operate at various suction pressures to support display cases operating at different temperatures. The hot gas from the compressors is piped to the condenser and converted to liquid. The liquid refrigerant is then piped to the receiver and distributed to the cases and coolers by the liquid manifold. After cycling through the cases, the refrigerant returns to the suction manifold and the compressors. Supermarkets tend to have one DX system for "low-temperature" refrigeration (e.g., ice cream, frozen foods, etc.) and one or two DX systems for "medium-temperature" refrigeration (e.g., meat, prepared foods, dairy, refrigerated drinks, etc.).

Source: International Energy Agency (IEA). 2003. "IEA Annex 26: Advanced Supermarket Refrigeration/Heat Recovery Systems, Final Report Volume 1-Executive Summary." Compiled by Van D. Baxter, Oak Ridge National Laboratory. April.

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Distributed System

Schematic of a Distributed Loop SystemUnlike traditional direct expansion refrigeration systems, which have a central refrigeration room containing multiple compressor racks, distributed systems use multiple smaller rooftop units that connect to cases and coolers, using considerably less piping. The compressors in a distributed system are located near the display cases they serve, for instance, on the roof above the cases, behind a nearby wall, or even on top of or next to the case in the sales area. Thus, distributed systems typically use a smaller refrigerant charge than DX systems and hence have decreased total emissions.

Source: International Energy Agency (IEA). 2003. "IEA Annex 26: Advanced Supermarket Refrigeration/Heat Recovery Systems, Final Report Volume 1-Executive Summary." Compiled by Van D. Baxter, Oak Ridge National Laboratory. April

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Secondary Loop System

Schematic of a Secondary Loop SystemSecondary loop systems have recently seen increased introduction into retail food equipment, and now make up about 4 percent of the market. These systems generally use R-404A or R-507A, although some earlier systems used R-22. Their average leak rate is between 2 and 15 percent.

Secondary loop systems use a much smaller refrigerant charge than traditional direct expansion refrigeration systems, and hence have significantly decreased total refrigerant emissions. In secondary loop systems, two liquids are used. The first is a cold fluid, often a brine solution, which is pumped throughout the store to remove heat from the display equipment. The second is a refrigerant used to cool the cold fluid that travels around the equipment. Secondary loop systems can operate with two to four separate loops and chiller systems depending on the temperatures needed for the display cases.

Source: Southern California Edison and Foster-Miller, Inc. 2004. "Investigation of Secondary Loop Supermarket Refrigeration Systems." Report prepared for California Energy Commission, Public Interest Energy Research Program. March.

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Technical Information on Advanced Refrigeration Technologies

In addition, advanced refrigerants can help reduce the climate impacts of supermarket refrigeration systems. See Acceptable Substitutes in Retail Food Refrigeration

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