Why Natural Refrigerants are Playing a Larger Role in Commercial Refrigeration

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In an era driven by historic regulatory activity and the necessity to deploy sustainable refrigeration system architectures, more businesses are looking at systems based on natural refrigerants to help them achieve these goals. Unlike the synthetic hydrocarbon (HFC) refrigerants that have commonly been used in refrigeration applications — such as R-404A, R-507A and HFC-134a — ammonia (NH₃ or refrigerant name R-717), propane (refrigerant name R-290) and carbon dioxide (CO₂ or refrigerant name R-744) are three naturally occurring refrigerants that pose very little threat to the environment.

The direct environmental impacts of refrigerants are measured by two key factors: global warming potential (GWP) and ozone depletion potential (ODP) — while their indirect impacts are measured by energy efficiency. While new synthetic refrigerants are being developed that offer lower GWP and no threat to the ozone layer, many of them are either largely untested or have yet to be deemed as acceptable substitutes by global environmental regulations, such as those set forth by the U.S. Environmental Protection Agency (EPA). In contrast, natural refrigerants are not only the benchmark for ultra-low GWP and ODP, they’re also acceptable for use in most refrigeration applications (subject to use conditions).

Let’s start by looking at the historic usage and performance characteristics of these natural refrigerants.

Ammonia
With its superior thermodynamic properties, R-717 was a logical first choice for early refrigeration systems. Classified as a B2L, its toxicity and mild flammability require the careful adherence to safe application procedures. The introduction of lower-risk, synthetic chlorofluorocarbon (CFC) refrigerants in the mid-twentieth century turned the refrigeration industry away from R-717. Even so, ammonia’s suitability in low-temperature applications has made it a mainstay in industrial, process cooling, cold storage and ice rink applications to this day.

Propane
Propane is a hydrocarbon that was also identified in the early days of refrigeration as an extremely effective refrigerant. Offering high-capacity, energy-efficient performance and a very low GWP (3), its A3 classification (flammable) led to concerns about its safety. And as synthetic refrigerants became available, R-290 was overlooked in favor of its CFC and HFC counterparts. However, since the 2000s, R-290 has been regaining global popularity as a lower-GWP, effective alternative to R-404A and HFC-134a — especially in a wide range of low-charge, reach-in displays.

Carbon dioxide
CO₂ is non-flammable and non-toxic and has proved to be a very effective natural alternative to HFCs in both low- and medium-temperature applications. CO₂-based refrigeration systems have been successfully deployed in commercial and industrial applications in Europe for nearly two decades. Because of its low critical point and high operating pressure (around 1,500 psig or 103 bar), CO₂ refrigeration strategies — such as cascade, secondary and transcritical booster — must be designed to account for its unique characteristics. In light of current environmental regulations, the popularity of these systems has increased significantly in North America in recent years.

Read the full Accelerate America article [pg.16].