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# Advanced Refrigeration

**Most of the 35,000+ supermarkets in the United States use centralized direct expa nsion (DX)**  **systems to chill their products. Typically, these refrigeration systems ar e charged with 3000 – 4000**  **pounds of refrigerant and can leak in excess of twenty percent of their charge each year . Commonly**  **used refrigerants include ozone-depleting hydrochlorofluorocarbon (HCFC) refrigerant s, often**  **HCFC-22, and blends consisting entirely or primarily of hydrofluorocarbons (HFCs), b oth of which**  **are potent greenhouse gases. Fortunately, in recent years there have been several advancements in**  **refrigeration technology that can help food retailers reduce both refrigerant char ges and refrigerant**  **emissions. Below is a general description of a centralized DX system as well as an overvie**  **w of the different advanced refrigeration options.**  On this page:

**• Centralized DX System** 
**• Distributed System**  **• Secondary Loop System**  **• Cascade System** 
**• Low GWP Refrigerants**  

### Centralized Direct Expansion System **At least 70 percent of stores in the United States use centralized DX system s to cool their display**  **cases and walk-ins. In a DX system, the compressors are mounted together and share suct ion and**  **discharge refrigeration lines that run throughout the store, feeding refrigerant to the ca ses and**  **coolers. The compressors are located in a separate machine room, either in the b ack of the store or**  **on its roof, to reduce noise and prevent customer access, while the condensers are usual ly air**  **cooled and hence are placed outside to reject heat. Page**  **1 of**  **5 Advanced Refrigeration | GreenChill | US EPA** 

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**- refrigeration** The 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 distribute d to the cases and coolers by the liquid manifold. After cycling through the cases, the refrigerant retur ns 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.). Schematic of a Centralized DX System

Source: International Energy Agency (IEA). 2003. "IEA Annex 26: Advanced Supermarket Refrigeration/Heat Recovery Systems, Final Report Volume 1-Executive Summ ary." 

### Distributed System Unlike centralized direct expansion refrigeration systems , distributed systems use multiple smaller units that are located close to the display cases that they serve. For instance, compressors in a distributed system may be located on the roof above the cases, behind a nearby wall, or even on top of or next to the case in the sales area. The close proximity of the compressors to thecases and coolers allows the system to use considerably less piping and additionally use a sma ller refrigerant charge than traditional DX systems. This reduction in charge often results in a decrease in total refrigerant emissions. Schematic of a Distributed System Page 2 of 5 Advanced Refrigeration | GreenChill | US EPA

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- refrigerationSource: International Energy Agency (IEA). 2003. "IEA Annex 26: Advanced Supermarket

Refrigeration/Heat Recovery Systems, Final Report Volume 1-Executive Summ ary." 

### Secondary Loop System 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; a primary refrigerant and a secondar y fluid. The secondary fluid is cooled by the primary refrigerant in the machine room and then pumpe d throughout the store to remove heat from the display equipment. Secondary loop systems typ ically ate with two to four chiller systems depending on the temperatures needed for the displ ay cases. Schematic of a Secondary Loop System Page 3 of 5 Advanced Refrigeration | GreenChill | US EPA

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- refrigeration**Source: Southern California Edison and Foster-Miller, Inc. 2004. "Investigation of Secondar y Loop**  **Supermarket Refrigeration Systems." Report prepared for California E nergy Commission, Public**  **Interest Energy Research Program.** 

### Cascade System **Cascade systems consist of two independent refrigeration systems that share a c ommon cascade**  **heat exchanger. Each system of a cascade system uses a different refrigerant that is most suitable**  **for the given temperature range. High temperature system uses high boiling point re frigerants such**  **as R-404A, R-507A, R-134A, propane, butane, and ammonia, whereas low temperature syste ms**  **use low boiling refrigerants such as R-744 (CO 2**  **) and R-508B. The advantages of a cascade system include a reduction in the refrigerant charge and a reduced carbon footprint.**  

### Low-GWP Refrigerants **Similar to advanced refrigeration technologies, low-GWP refrigerants can also r educe the climate**  **impacts of supermarket refrigeration systems. Refrigerants such as car bon dioxide (CO**  **2 ), ammonia,**  **hydrocarbons, and hydrofluoro-olefins (HFOs) have potential to be used in commercial refrigeration systems in the U.S. market. Currently only CO**  **2 is being used as a primary refrigerant**  **in commercial refrigeration system applications in the United States. Ref rigeration systems that use**  **CO 2**  **as a primary refrigerant are commonly referred to as transcritical CO 2**  **systems. Transcritical CO**  **2 refrigeration is a type of refrigeration cycle in which CO**  **2 is the sole refrigerant, evaporating in**  **Page 4**  **of 5**  **Advanced Refrigeration | GreenChill | US EPA**

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**- refrigeration** **the subcritical region and rejecting heat at temperatures above the critical point in a gas cooler** 

**instead of a condenser. For more information on acceptable low-GWP refrigerants, s ee**  **Acceptable Substitutes in Retail Food Refrigeration**  **.**

Last updated on March 16, 2014 **Page 5**  **of 5**  **Advanced Refrigeration | GreenChill | US EPA**

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**- refrigeration**