Low Global Warming Potential Refrigerants

You probably have heard that the most popular HFC refrigerants being widely used today are global warming gasses. In fact, some popular HFC refrigerants have higher GWPs than the CFCs and HCFCs they replaced. A refrigerant’s Global warming potential (GWP) compares it to CO², the global warming gas produced by burning hydrocarbons. A GWP of 1 indicates that a gas has the same effect on global warming as CO². The retired popular air conditioning refrigerant, HCFC 22, has a GWP of  1760. HFC 410A that is now widely used in air conditioning applications has a GWP of 1924. It is actually worse! Meanwhile HFC 404A, popular in refrigeration applications, has a GWP of 3943. HFC 134a is popular in domestic refrigerators, commercial refrigeration, and car air conditioning has a GWP of 1300. These high GWP numbers have made HFC refrigerants the target of regulatory efforts to limit their use and replace them with more environmentally friendly refrigerants. Europe has moved aggressively, passing their F-Gas regulations. The ultimate objective of the F-Gas Regulations is to cut the availability of HFCs by 79% between 2015 and 2030. There will also be a servicing ban on HFCs with a GWP >2500 for certain sectors. Here is a link to a quick overview of the F-Gas regulations byMitsubishi.

While the US has not moved nearly as aggressively, there have been attempts by the EPA to regulate refrigerants based on their GWP. Worldwide regulatory restrictions on current HFC refrigerants has spurred development of lower GWP refrigerants. Manufacturers in the HVACR industry have been actively developing lower GWP alternative refrigerants.

HYDROCARBONS

Propane (R290), Isobutane (R600a), and R441A all have very low GWPs of (3, 3,0). They are all non-ozone depleting and non-toxic. Their limitation is their flammability – they are all highly flammable. In the US they are approved only for systems with a charge of 150 grams (5 ounces) or less. In Europe hydrocarbon refrigerants have been used in refrigerators and freezers for years. These refrigerants are now common in residential refrigerator and small commercial refrigeration units in the US. While highly flammable refrigerants are likely to remain a factor in small commercial refrigeration systems, it is unlikely that these refrigerants will be used in larger systems in the US due to our aversion for being sued and the large number of lawyers in the US.

CO² R744

It is interesting that the main global warming culprit, CO², is also a refrigerant with a very low GWP of 1. It does not deplete the ozone, it is non-toxic, non-flammable, and cheap. What’s not to like? Unfortunately, CO² has a critical temperature of 88°F. It cannot condense above 88°F. This means that CO² systems are not “normal” systems. CO² systems must either be transcritical or cascade systems. Transcritical systems operate at very high pressures of 1200 – 1500 psig on the high side. Cascade systems use the evaporator of one system to cool the condenser of another system. Either way, CO² systems are more complicated and expensive than traditional system. One place that CO² has taken root is in large scale commercial refrigeration rack systems. Complexity in large rack refrigeration systems is normal and the extra cost of the transcritcial components is offset by the savings in refrigerant cost. However, in smaller scale systems the cost of a CO² system is prohibitive. For a quick explanation of a transcritical system check out https://www.achrnews.com/articles/94092-co2-as-refrigerant-the-transcritical-cycle

AMMONIA R717

Ammonia refrigeration has been around since the earliest days of refrigeration. Ammonia has always been used in large scale food commercial refrigeration and freezing for food processing because of its efficiency and low cost. Unfortunately, ammonia (R-717) has many application challenges. It is toxic, somewhat flammable, and cannot be used with some metals, such as brass or copper. It will continue to be a mainstay of commercial food processing, but I doubt you will see it expand into other market segments.

LOWER GWP HFCs

There are some HFC refrigerants that have a GWP in the hundreds instead of the thousands. While these refrigerants are probably not long-term solutions, they can provide a way to drastically reduce the GWP footprint of a system without a drastic change in technology or design.

R 32

HFC R-32 has been adopted by many manufacturers in air conditioning systems sold outside of the United States. R-32 is an HFC with a lower GWP of 667. That is still not really low compared to CO2 (GWP 1) or ammonia (GWP 0), but it is considerably lower than R404A, R410A, or R134a. HFC32 has the advantage of being a relatively “normal” refrigerant, making designing systems to use it less challenging than say, CO². However, R-32 is flammable. While not as flammable as propane, it does burn. That precludes its use in most applications in the US, at least right now. The building and safety codes in the US do not allow a flammable refrigerant in systems where the air in the building flows directly over the evaporator. These codes make no distinction between A2L and A3 refrigerants. To them, flammable is flammable.  Manufacturers and code officials in the US are working to determine what new requirements an A2L refrigerant system should have to make it safe for use. The one place you will find R32 in the US is in window air conditioners. The EPA allows use of R32 in limited quantities in window units. Here is a link for more information on R32. 

R466A (Solstice N41)

Honeywell has developed an A1 rated, non-flammable HFC based refrigerant with a GWP of 733. Like R-32, R-466A provides a refrigerant with a much lower GWP than HFC refrigerants currently in use, but not really low. Its big advantage over R32 is that it is non-flammable. R466A achieves this by using a mix of 49% R32, 11.5% R125, and 39.5% R1311. R32 and R125 are the two components found in R410A. R1311 has been previously used as a fire suppressant. This blend performs similarly to R410A, making adoption relatively easy.  Here is a link to more information on R466A. 

HFOs

Hydrofluoroolefins (HFOs) are a special type of HFC. They have at least one carbon double bond, making them less chemically stable than a “normal” HFC which has all single bonds. Because they are less chemically stable, they do not persist in the atmosphere for long, and this reduces their global warming potential. For example, HFO1233zd has a GWP of 0. HFO1233zd is a low pressure refrigerant for chiller applications. It has an A1 safety rating and does not deplete the ozone. HFO1234yf has a GWP less than 1. It has an A2L safety rating – meaning that it is somewhat flammable. HFO1234yf is used in auto air conditioning systems. It has been what most auto manufacturers now use instead of HFC134a. Here is a link to more information on HFOs.

R1234ze

R1233zd

R1234yf 

Lower GWP refrigerants are the future of HVACR. Some old and some new. Understanding how to safely work with these lower GWP refrigerants will be an important part of all technician’s knowledge set going forward.