The cold storage market in the United States is growing and there are several factors to consider when designing new facilities including the choice of refrigerant. Traditionally, large cold storage projects have used ammonia plants, while smaller projects have used HFC refrigerants such as R404A or similar blends. However, recent EPA regulations have restricted the use of HFC refrigerants pushing cold storage facility designers to consider and explore other more sustainable options.
Large Cold Storage Facilities
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Traditionally, large distribution center cold storage projects have used ammonia plants to serve their refrigeration needs. Ammonia is a very efficient refrigerant and is most used with “flooded” evaporators that increase the amount of refrigeration effect by utilizing the entire evaporator surface area and having a larger enthalpy phase change per pound of ammonia pumped through the system. The efficiency differences cause the piping to be 10-20% smaller since the system uses less mass flow of refrigerant.
The compressor selections for ammonia include large screw compressors. Ammonia plants, sometimes called machine rooms, often serve an entire facility with a small number of low and medium temperature screw compressor and a swing compressor capable of either low or medium temperature. Since it is a natural refrigerant, ammonia does not impact global warming if released to the atmosphere.
While it offers a plethora of benefits, ammonia is not right for all applications. Ammonia is rarely, if ever, utilized in grocery stores since it is considered hazardous by the OSHA Hazard Communication Standard (29 CFR 1910.1200) and is flammable if exposed to high heat.
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Additionally, the vessels in the central plant must be sized to carry the system charge, including the potential for large surge capacities. In some instances, the machine room may be a long distance from some of the spaces it serves, so long piping runs also can result in significant charge and piping costs, because copper is not compatible with ammonia. Conversely, packaged ammonia systems or transcritical CO2 racks can be strategically located throughout buildings so they are close to the spaces they serve.
Extensive training is required for operators and employees in facilities featuring ammonia systems and full-time maintenance personnel are required as part of the ongoing operational costs. Systems that contain 10,000 or more pounds of ammonia are required to comply with OSHA regulations and are required to complete a Process Hazard Analysis (PHA) every five years.
Small Cold Storage Facilities
For smaller cold storage facilities (fulfilment centers smaller than 40,000 square feet), there are fewer options available. One option is to use a low-pressure HFO refrigerant such as R471a. However, R471a has a GWP of 159, which is below the EPA’s limit of 300 for new cold storage facilities. A second option is transcritical CO2 systems, also called booster CO2 systems. Booster CO2 refrigeration systems are a better option for small cold storage facilities that need a refrigerant with a GWP of less than 300. However, transcritical CO2 systems have a higher initial cost than other types of systems and require significant training to operate and maintain.
Refrigeration Restrictions
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The Global Warming Potential (GWP) metric was developed to allow comparisons of the impacts of different refrigerants on global warming. It specifically measures how much energy the emissions of one ton of a gas will absorb over a given period relative to the emissions of one ton of carbon dioxide. Every other gas is compared to CO2, which has a GWP of one. For example, the GWP of R404A is 4,808; this means it has 4,808 times the impact on global warming as compared to CO2. A final EPA ruling from October 2023 added several key restrictions to refrigerants based on GWP that will go into effect January 1, 2026:
- 150GWP limit for cold storage warehouses with 200 lbs. or more refrigerant charge, not including the high-temperature side of cascade systems.
- 300GWP limit for cold storage warehouses with less than 200 lbs. refrigerant charge.
- 300GWP limit for high-temperature side of cascade systems.
- Comparable limits are in place for other facilities including retail food refrigeration systems, industrial process refrigeration, refrigerated transport, chillers, data centers, ice rinks, air conditioning, and heat pumps.
Conclusion
The best refrigeration option for a cold storage facility depends on several factors, including the size of the facility, the type of products being stored, the climate, and the budget. For large cold storage facilities, ammonia plants and packaged ammonia systems are both good options, as well as transcritical CO2 systems. Transcritical CO2 systems are also a good option in small cold storage facilities. It is important to consider all the available options when meeting the specific needs of the facility while also ensuring the facility’s refrigeration systems are compliant with all applicable regulations.
Henderson Knows Sustainable Refrigeration
With more than 50+ years of experience in refrigeration design across retail, grocery stores, cold storage, and distribution centers, we’ve worked on every facility type and size, including two of the largest CO2 cold storage projects in the US. We understand how refrigerants align with corporate sustainability goals, and we constantly monitor the evolving regulatory landscape and are currently working with seven of the 10 biggest retailers and grocers in the world to help with their climate pledge goals. Learn more about our expertise on sustainable refrigeration design by clicking here.
The GWPs listed in this article are the 100-year GWP from the UNEP’s RTOC 2022 report to be consistent with industry standards, however Henderson acknowledges that the 20-year GWP time horizon is a better analog when discussing the immediate climate change impact of refrigerants.
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