2023. 5. 31.
A2L and A3 refrigerants: flammable substances with future potential
Among other things, increasingly stringent environmental regulations, most notably EU F-Gas Regulation 517/2014 in Europe, make low-GWP refrigerants all the more important. Because many of these substances belong to the A2L and A3 safety classes, they’re flammable and require a special hazard assessment. How do flammable refrigerants differ in terms of sustainability? What do you need to take into account when installing and servicing systems with these substances and what could efficient components look like? BITZER offers a large portfolio of approved components and an extensive selection of training courses to assist its customers in the use of flammable refrigerants.
Flammable substances have long been used in household appliances and commercial refrigeration. In addition to ammonia, sulphur dioxide and carbon dioxide, use of non-toxic, but highly flammable, hydrocarbons increased around the end of the 19th century due to their good thermodynamic properties. For example, propane (R290) is suitable for use in commercial refrigeration. It has a boiling point of -42°C and can evaporate at temperatures of -40°C and higher. Compression with this substance can accommodate large fluctuations in temperature without any issues.
Hydrocarbons – highly flammable refrigerant with exemplary performance
When the first synthetic refrigerant was developed, the aim was to match the good thermodynamic properties of hydrocarbons, whilst reducing flammability, and thus improve safety and simplify installation. Hydrogen was largely replaced with the halogens chlorine and fluorine and to a lesser degree with bromine, resulting in the first safety refrigerant. Launched in the 1930s, fully halogenated CFC soon drove out many of the other substances used in commercial refrigeration and household appliances.
Because chlorine and bromine contribute significantly to the depletion of the ozone layer, today’s synthetic refrigerants are primarily fluorinated hydrocarbons. Whilst most of those are partially fluorinated, some are based on monounsaturated hydrocarbons such as propylene, which shortens the atmospheric lifetime and reduces global warming potential. In addition, pure hydrocarbons are still used as refrigerants in a variety of applications such as process cooling in the petrochemicals sector, in commercial refrigeration equipment and in liquid chillers.
An overview of flammable refrigerants
In accordance with the ISO 817 standard, refrigerants are now broken down into Categories A and B. Non-toxic substances belong in Category A, toxic refrigerants in Category B. The degree of flammability is broken down into four groups (1 = non-flammable, 2L = flammable with slow spread of flames, 2 = flammable, 3 = highly flammable).
The most important substances in safety group A3 that offer potential as a refrigerant are hydrocarbons such as propane (R290), propylene (R1270), isobutane (R600a), butane (R600) and ethane (R170), which, as explained, have a long history in the refrigeration and air conditioning industry and served as an example in the development of many synthetic refrigerants. Group A3 refrigerants are extremely flammable and can ignite at concentrations of two to ten per cent in the air. In a medium concentration, the mere spark of a light switch, a steel tool dropped onto the floor or a statically charged pullover could result in ignition and lead to serious deflagration or explosion. The combustion residues tend to be carbon dioxide and water and are therefore the least dangerous, once everything has had a chance to cool.
The most common refrigerants in the A2L class are hydrofluorocarbons (HFCs), hydrofluoroolefins (HFOs) and blends of the two. Low fluorination reduces the level of flammability, whilst offering low or moderate global warming potential. Examples include R1234yf, R32 and R455A. Compared to A3 refrigerants, A2L refrigerants are heavier and capable of ignition at higher concentrations. Flames and serious electrical faults, for example, can provide the necessary ignition energy. In addition to carbon dioxide and water, combustion can also result in high levels of toxic and corrosive residues such as hydrogen fluoride – hydrofluoric acid dissolved in water – and carbonyl fluoride, meaning more intensive precautionary measures need to be taken after combustion.
In a given space, A2L refrigerants can often accommodate much higher charges and therefore higher cooling capacities with the same safety guidelines and without increasing the level of risk. This is advantageous particularly when it comes to compact air conditioning systems and heat pumps. But as long as each refrigeration system is optimally adjusted for the refrigerant in use, there’s no discernible difference between A2L and A3 refrigerants in terms of system efficiency.
| Refrigerant | R290 | R1270 | R600a | R1234yf | R454C | R455A | R32 | R404A | R410A | R134a |
|---|---|---|---|---|---|---|---|---|---|---|
| Safety Class | A3 | A3 | A3 | A2L | A2L | A2L | A2L | A1 | A1 | A1 |
| Molecular mass [g/mol] | 44,1 | 42,1 | 58,1 | 114 | 90,8 | 87,5 | 52 | 97,6 | 72,6 | 102 |
| Normal boiling point (dew point) [˚C] | -42,1 | -47,6 | -11,6 | -29,5 | -45,6 (-37,8) | -52 (-39,2) | -51,7 | -46,2 | -51,4 | -26,1 |
| Liquid density 40˚C [kg/dm³] | 0,47 | 0,48 | 0,53 | 1,03 | 0,98 | 0,97 | 0,96 | 0,97 | 0,98 | 1,15 |
| Vapor pressure (abs) -10˚C [bar] | 3,45 | 4,3 | 1,08 | 2,2 | 3,2 | 3,4 | 5,8 | 4,34 | 5,72 | 2,01 |
| Vapor pressure (abs) +40˚C [bar] | 13,7 | 16,5 | 5,3 | 10,2 | 14,6 | 15,6 | 24,8 | 18,2 | 24,1 | 10,2 |
| Critical temperature [˚] | 96,7 | 91,1 | 134,7 | 95 | 86 | 86 | 78 | 72 | 71,3 | 101,1 |
| Lower explosion limit [vol ] | 1,7 | 2 | 1,8 | 6,2 | 7 | 11,8 | 13,8 | - | - | - |
| Upper explosion limit [vol %] | 10,9 | 11,1 | 8,5 | 12,3 | 15 | 12,9 | 29,9 | - | - | - |
| ODP | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| GWP AR4 | 3 | 3 | 3 | 4 | 148 | 148 | 675 | 3922 | 2088 | 1430 |
| GWP AR 6 | <<1 | <<1 | <<1 | <<1 | 166 | 166 | 771 | 4728 | 2256 | 1530 |
A2L refrigerant and potential PFAS bans in the EU
The current debate surrounding a potential ban on per- and polyfluoroalkyl substances (PFASs) could have an impact on the long-term availability of many A2L refrigerants. According to the definition of the proposed ban, the PFAS substance group covers many HFCs, including HFOs, which due to their low greenhouse effect and low flammability were a preferred solution for fulfilling the requirements of the EU F-Gas Regulation. Authorities in Germany, the Netherlands, Denmark, Sweden and Norway have recommended listing PFASs as substances of concern in EU Regulation 1907/2006 (REACH) on chemicals, which would make it much more difficult to use PFASs or prohibit them entirely. It’s too soon to accurately predict the results of the debate. However, a potential ban on all alternative refrigerant blends with low GWP would make highly flammable and eco-friendly hydrocarbons in safety group A3 all the more important in the refrigeration and air conditioning industry in the future.
Safety aspects when using flammable refrigerant
Regardless of the flammable refrigerant selected, an expanded risk assessment for work environment needs to be conducted before these substances can be used. Specially trained, well-informed staff are a basic requirement and will need to have knowledge of current legislation, regulations and standards as well as the skills necessary to work with flammable refrigerants. Operators should test for the corresponding knowledge necessary for working on the system. Regular training courses for specialists in this area are recommended – for example, at the SCHAUFLER Academy.
When it comes to installing the refrigeration system, work is carried out in accordance with the established rules, even if the refrigerant is flammable. Most important is raising awareness of potential flammability and the risk of explosion when using the refrigerant. Safety becomes more of an issue when maintaining and servicing the system, provided the system is already charged and may need to be opened, in which case maximum safety precautions need to be taken to minimise the risk of accident. Under no circumstances should an explosive atmosphere be allowed to form. More stringent requirements need to be observed particularly when it comes to A3 refrigerants. Due to the extreme oil solubility of hydrocarbons, there is also the risk that the oil may outgas dangerous amounts of refrigerant even after the extraction process.
The following aspects are just some of the issues that need to be considered when maintaining and servicing the system (list incomplete):
- Good space ventilation – for example, with a fan brought along
- Ensuring there are no ignition sources nearby
- Personal protective equipment such as a portable gas detector and anti-static gloves
- Approved ‘non-sparking’ tools
- Gas sensors and shut-off equipment
- Suitable fire extinguishing equipment
Efficient components for systems with flammable refrigerants
BITZER teaches its customers how to use flammable refrigerants with manuals and practical training courses at the SCHAUFLER Academy. In addition, the refrigeration, air conditioning and heat pump specialist’s portfolio features a wide range of products approved for use with flammable refrigerants, including those in the A3 class. These products include oil separators, liquid receivers, condensers, evaporators, reciprocating compressors of different construction sizes, compact screw compressors for the high temperature range and process cooling, and semi-hermetic screw compressors for compound systems in commercial refrigeration.
The optional VARISTEP mechanical capacity control is available for compressors to increase the system’s part load efficiency. Alternatively, the equipment with VARIPACK frequency inverters ensures precise adjustment in line with cooling demand. Many of the BITZER reciprocating compressors approved for flammable refrigerants can be equipped with the OLM-IQ electronic oil level switch, which helps stabilise the oil level in the compressor and prevent a drop in oil. The IQ MODULE allows you to connect products to the BITZER Digital Network (BDN), which is based on the compressor expertise of BITZER and creates a service infrastructure for increased operation efficiency and high availability of components.
