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The food retail, foodservice and industrial cooling industries are in the midst of a momentous transition in refrigeration system architectures. Regulations are driving the need to implement sustainable systems with options growing exponentially. Emerson’s natural refrigerant expert, Andre Patenaude, provides advice on the best alternatives to future proof your system.

To get to what many call the “end game” of achieving compliance and meeting corporate sustainability objectives, more businesses are looking at systems based on natural refrigerants to help them achieve these goals.

The term “natural refrigerant” refers to substances that naturally occur in the environment. Unlike the synthetic refrigerants that have commonly been used in refrigeration applications — including hydrofluorocarbons (HFCs) and chlorofluorocarbons (CFCs) — 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.

While new synthetic refrigerants are being developed that offer lower GWP and no threat to the ozone layer, many of these are either largely untested or yet to be deemed as acceptable substitutes by global environmental regulations, such as those set forth by the US 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).  This is why its important to know your naturals.

Ammonia was among the first refrigerants used in refrigeration applications. While its superior thermodynamic properties made it a logical first choice for early refrigeration systems, its toxicity requires the careful adherence to safe application procedures to ensure operator and customer well-being.

With the advent of CFC refrigerants in the mid- twentieth century, the refrigeration industry moved away from R-717 in favor of lower risk synthetic alternatives that offered comparable performance characteristics. Even so, ammonia’s suitability in low-temperature applications has made it a mainstay in industrial, process cooling, cold storage and ice rink applications.

Another natural to consider is hydrocarbons. Propane is a hydrocarbon that was also identified in the early days of refrigeration as an effective refrigerant.

Its high-capacity, energy-efficient performance and very low GWP are offset by its classification as an A3 (highly flammable) substance. But as synthetic refrigerants became available for many refrigeration applications, R-290 was largely abandoned in lieu of its CFC-based counterparts. Since the 2000s, R-290 has been regaining global popularity as a lower- GWP, effective alternative to HFCs like R-404A and HFC-134a — especially in a wide range of low-charge, reach-in display .

CO2 is non-toxic and has proved to be a very effective 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 recent years.

When reviewing the brief application history of these refrigerants and their synthetic counterparts, it’s apparent that the search for the perfect refrigerant is an ongoing quest. It’s important to keep this in mind when evaluating natural refrigerants. Yes, efforts are needed to mitigate their associated risks and ensure their safe use, but natural refrigerants represent true sustainable alternatives without sacrificing performance.

Today, the use of natural refrigerants is on the rise. Companies are taking a fresh look at them to achieve their sustainability objectives, whether that’s complying with environmental regulations or aligning with their customers’ green sensibilities. As technology continues to improve, equipment manufacturers are working closely with these forward-thinking companies to develop innovative solutions.

This has resulted in several creative natural refrigeration applications like ammonia being used in supermarket systems and CO2 playing a larger role in industrial process cooling.

For example, the Piggly Wiggly supermarket is using a NH3/CO2 cascade system manufactured by Heatcraft Worldwide Refrigeration. The all-natural refrigerant system uses an ultra-low charge of ammonia (53 pounds) located on the facility’s roof.

The ammonia condenses the CO2 and is circulated to the store’s low- temperature cases via direct expansion; the medium-temperature circuit is cooled by a CO2 liquid pump overfeed.  In its first six full months of operation, this store consumed 28.5 per cent less energy.

In cold storage applications, where ammonia has been the preferred refrigerant for decades, companies are also seeking to lower ammonia charges. As older ammonia systems near replacement, many operators are evaluating the best option to expand their facility’s low-temperature capabilities.

They’re accomplishing this by adopting NH3/CO2 cascade systems that not only utilize very low charges of ammonia, but also keep the R-717 circuit out of occupied spaces. There’s also a regulatory driver behind this trend.

To ensure the safety of systems that require more than 10,000 pounds of ammonia2, the Occupational Safety and Health Association (OSHA) created the Process Safety Management of Highly Hazardous Chemicals (29 CFR 1910.119)3 standard. In recent years, these systems have been subject to rigorous inspections enforced by OSHA’s National Emphasis Program4 (NEP) on process safety management regulated industries.

For owners and operators of these large ammonia systems, this means the added responsibility — and expense — of continuous record keeping in preparation for NEP inspections.

When major retailers like Target announce their intentions to use only propane in their self-contained units, it’s an indication that the perceptions about the mainstream viability of R-290 are shifting. The smaller charge limits make R-290 a logical fit for Target’s smaller, stand-alone refrigerated display cases and coolers.

All of this is part of the retailer’s pledge to become a sustainability leader in the food retail space. In making this shift, Target has also asked contractors who might be working on the propane-based equipment to seek the necessary training. Over the next six months, Target plans on opening a few stores that will use only stand-alone propane systems.

CCN's Special Series

This article is the first in a series to be published by CCN dealing with natural refrigerants. The series will cover costs, energy efficiency, safety, maintenance and compliance.

Whether you’re selecting 1,000 tonnes of refrigeration, or specifying a few walk-in coolers for a restaurant or convenient store, the number of system sizes and options can be daunting to evaluate.

To help your organization wade through the confusion and make these difficult decisions, this series will look at the potential of natural refrigerants in modern refrigeration equipment.

Next month, the series will examine R-290 in small, stand-alone systems and other emerging architectures.

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