Alternate Refrigerants: The Industry Wide Transition to Low Global Warming Potential (GWP) Solutions.
For thousands of years, scientists have researched, simulated, and theorized about our ever-evolving environment. Additionally, the humankind environmental footprint has been small for most of our time on Earth, and, up until the twentieth century, or shortly after the industrial revolution, no one even considered that humankind could both negatively and positively change the place we call home. However, as new technologies have been introduced to understand the Earth’s reaction to our footprint, only within the last forty years have humans focused to change the Earth’s trajectory regarding ozone depletion, global warming, and climate change.
It first started with the Montreal Protocol, finalized in 1987, to begin the phase-out of the production and consumption of ozone-depleting substances (ODS) as scientists found growing concern with the “hole” in the ozone layer which is believed to be caused mainly by chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs). It is widely believed that reducing CFCs and HCFCs (such as refrigerants R-12 and R-22 respectively) is critical in ozone protection because when these refrigerants are exposed to intense UV light the chlorine separates from the compound and destroys ozone molecules. Per the Environmental Protection Agency (EPA), one chlorine atom can destroy over 100,000 ozone molecules before it’s removed from the stratosphere.
The Montreal Protocol, which was adopted by many countries around the world, established a phase-out of CFCs by 2010 and HCFCs by 2040 globally. Developed countries had stricter timeframes than developing countries.
This table contains the more commonly used hydrocarbon, HFO-blend, and HFO refrigerants in comparison to “legacy” refrigerants within distributed commercial refrigeration applications. As GWP decreases, flammability tends to increases. Source: Tecumseh
After the success of the CFC phase-out and planned HCFC phase-down due to the Montreal Protocol, in 1997 the Kyoto Protocol was established to reduce the emissions of greenhouse gases, such as a global reduction of carbon dioxide (CO2) emissions. Although this is not as widely adopted as the Montreal Protocol, the Kyoto Protocol began the overall reduction of greenhouse gas production and usage which impacts global warming. Global warming potential (GWP) is a relative measure of how much heat a greenhouse gas traps in the atmosphere, and specific refrigerants used in commercial refrigeration may have high or low GWP levels based on their composition.
Unfortunately, the most widely accepted substitutes for CFCs and HCFCs were hydrofluorocarbons (HFCs), which tend to have high GWP. In fact, some HFCs have even higher GWP values than HCFCs with R-404A and R-134a being some of the more commonly used HFC refrigerants in commercial refrigeration. These higher and lower pressure refrigerants, respectively, were, from a refrigeration technical perspective, great substitutes for CFCs and HCFCs; however, if leaked into the atmosphere, they may do significant damage to the environment indirectly.
This chart contains guidelines on refrigerant classification. R-290 (Propane) is A3 classification while traditional HFCs such as R-404A is A1 classification. LFL or lower flammability limit defines the range of flammable concentrations in air which can help reduce the overall risk of fire. Source: EPA
Fast-forward to 2018 and we are now at a point where countries are implementing legislation such as the United States’ EPA’s Significant New Alternatives Policy (SNAP) program from the Clean Air Act, or the European Union’s F-gas Regulation, intended to reduce global warming potential (GWP) refrigerant usage. These are also driven by new global initiatives such as the Paris Agreement that has a plan, like previous global agreements, to phase-out specific substances that are thought to be harmful to the environment.
Within the United States, beginning in 2015, the EPA implemented a rule within the SNAP program to begin the phase-out of HFCs in specific applications. Commercial refrigeration was impacted quite drastically by the new regulations that began as early as 2016 for retrofit equipment.
You may be thinking that this is no big deal, we’ve done this in the past for other substances such as the transition from R-22 to R-404A or R-12 to R-134a, and we’ve been able to do this seamlessly. So why does this keep coming up every year as a major topic of discussion? Just as in compressor or system design, there are always trade-offs, and it comes down to the physical properties of these refrigerants and the resulting performance in an application.
As the GWP of a substance or refrigerant is lowered, other unfavorable characteristics begin to arise. Several refrigerant characteristics plaguing the industry today are temperature glide, flammability and system operating window. These characteristics can drastically impact system design, servicing, and overall performance which can end up being costly to the manufacturer and end-user. I will briefly touch on these constraints, but there are many other considerations to be reviewed.
Temperature glide – this is the temperature difference between the saturated vapor temperature and the saturated liquid temperature at a constant pressure. Zeotropic refrigerants such as hydrofluro-olefin (HFO) blends exhibit temperature glide which can change sub-cooling and superheat requirements to manage the energy transfer between vapor and liquid state.
Special precautions must be taken to ensure reliable compressor operation, hence, limited operating windows regarding evaporating temperatures, condensing temperatures, and superheat conditions. Source: Tecumseh
Flammability – obviously safety concerns arise if you are using a refrigerant that is considered flammable. Hydrocarbons, such as R-290 and R-600a, both becoming more commonly used in commercial refrigeration as well as residential refrigerators and freezers, are highly flammable and there currently are limited official, un-biased service technician certifications for handling and servicing equipment with these types of refrigerants.
System operating window – certain short-term HFO-blend refrigerants have higher discharge compressor temperatures than HFC refrigerants which can limit the operating conditions of equipment or potentially shorten the life of the compressor. Typically, liquid or vapor injection into the compressor or system is required to mitigate this concern, however, this can be costly and require additional control expertise in operating the equipment.
Commercial refrigeration has a wide variety of banned, under review, and approved substances with phase-out dates that are dependent on application type. Due to recent litigation against the EPA (https://www.gpo.gov/fdsys/pkg/FR-2018-04-27/pdf/2018-08310.pdf), these specific phase-out dates for HFCs in the United States are in limbo and no longer in effect. Source: Tecumseh *Click on the image to view a larger version.
R-407A, R-448A, R-449A Application Boundaries
Overall, many next generation refrigerants can be viable solutions in the right applications. However, there is no longer a “one-size fits all” solution for each application, especially since governmental regulation often dictates what can and cannot be used. Additionally, many times there is a lengthy process to get an approved refrigerant from an industry organization or governmental agency.
In conclusion, there are several steps a commercial refrigeration manufacturer can take in this process and it depends on investment and goals to have a sustainable solution either short-term or long-term.
It is generally agreed that there are three potential options:
Option 1: Make the leap to natural refrigerants that have a potential to be flammable, toxic, or difficult to work with, and which may require a large capital investment to be in alignment with safety and industry wide standards.
Option 2: Live with the short-term next generation of HFO-blend refrigerants that are non-flammable, but expect a significant reduction in performance and an increase in cost. These refrigerants are not considered “drop-in” replacements for HFC refrigerants.
Option 3: Plan the development around a slightly flammable HFO-blend (A2L) that will likely become more widely accepted over the next couple years. These refrigerants may or may not be long term solutions but, depending on research across the industry, they might have a good chance of becoming more permanent than other solutions.
Pros – The “one-and-done” approach with moving to a long-term sustainable refrigerant. Performance can exceed current HFC refrigerants.
Cons – Charge limitation on natural refrigerants (example is 150 grams of R-290 in self-contained refrigeration applications), specifically for the ones that are highly flammable. Most of these refrigerants are tough to design around, can be dangerous to work with, can be expensive to integrate into manufacturing, and may require special modifications to assembly lines.
Pros – Quickly become much “greener.” Most compressor and system manufacturers have already approved these refrigerants in existing offerings with no major change to product design.
Cons – There is no industry-wide agreed upon refrigerant of choice and are dependent on user or manufacturer preference. Most likely expect another refrigerant change within three to five years. Temperature glide can be an issue, and most contractors do not understand how to retrofit or replace with a non-flammable HFO-blend.
Pros – Europe is already adopting A2L refrigerants as a solution for commercial refrigeration applications. Most A2L refrigerants are less than 150 GWP, and that seems to be a threshold for most legislators today.
Cons – Similar cons to Option 2 along with uncertainty regarding system charge limits.
As you can see, there is no one right answer. Due to the unforeseen political landscape across the globe and directional change on what GWP level is considered reasonable, the choice is dependent on where you as a manufacturer or user feel comfortable with the amount of risk that you want to take. Even if governments world-wide state that HFCs can be used, based on the forty years plus of global alignment, two things will not change: the desire for humankind to be more in tune with our environment and the continued push to have a healthy and safe place to live.
This article is provided for general informational purposes only and there is no guaranty as to the accuracy of the information. Readers use the information at their sole risk and are responsible to independently verify the information.