Refrigerants are substances that are used to transfer heat in cooling systems, such as air conditioners, refrigerators, freezers, and heat pumps. Refrigerants can be classified according to their chemical structure, ozone depletion potential (ODP), global warming potential (GWP), and flammability. Flammability is a measure of how easily a refrigerant can ignite and burn when mixed with air.
One of the newest classes of refrigerants is hydrofluoroolefins (HFOs), which are unsaturated organic compounds composed of hydrogen, fluorine, and carbon. HFOs have zero ODP and very low GWP, making them more environmentally friendly than traditional hydrofluorocarbons (HFCs) and chlorofluorocarbons (CFCs). But are HFOs flammable? And if so, why are they less flammable than other refrigerants?
HFO refrigerants are mildly flammable or non-flammable, depending on the type and concentration of HFO. HFOs are less flammable than other refrigerants because they have a double bond between two carbon atoms, which makes them more reactive and less stable. This means that HFOs break down faster in the atmosphere and do not accumulate in high concentrations. HFOs also have lower heat of combustion and lower burning velocity than other refrigerants, which means they release less energy and burn slower when ignited.
In this post, we will explain more about the flammability of HFO refrigerants, their advantages and disadvantages, and how they compare to other refrigerants. We will also answer some frequently asked questions about HFO refrigerants. By the end of this post, you will have a better understanding of why HFO refrigerants are less flammable and whether they are suitable for your cooling needs.
What is the flammability of HFO refrigerants?
The flammability of HFO refrigerants is determined by several factors, such as their chemical structure, molecular weight, boiling point, vapor pressure, heat of combustion, burning velocity, lower flammability limit (LFL), and upper flammability limit (UFL). These factors affect how easily a refrigerant can form a combustible mixture with air, how much energy it releases when it burns, and how fast it burns.
The flammability of refrigerants is classified according to the ASHRAE Standard 34-2019 , which assigns a safety classification based on toxicity and flammability. The toxicity classification is either A (lower toxicity) or B (higher toxicity), while the flammability classification is either 1 (no flame propagation), 2L (lower flammability), 2 (flammable), or 3 (higher flammability).
Most HFO refrigerants have an A2L safety classification, meaning they have lower toxicity but lower flammability. This means that they can ignite and burn under certain conditions, but they have a low risk of fire or explosion. Some examples of A2L HFO refrigerants are R-1234yf, R-1234ze(E), R-1233zd(E), R-1336mzz(Z), R-445A, R-447A, R-448A, R-449A, R-450A, R-452B, R-454A, R-454B, R-454C, R-455A, R-457A, and R-513A.
Some HFO refrigerants have an A1 safety classification, meaning they have lower toxicity and no flame propagation. This means that they are non-flammable under any conditions. Some examples of A1 HFO refrigerants are R-1234ze(Z) and R-514A.
Some HFO refrigerants have a B2L safety classification, meaning they have higher toxicity but lower flammability. This means that they can ignite and burn under certain conditions, but they have a low risk of fire or explosion. However, they may pose health hazards if inhaled or exposed to skin or eyes. Some examples of B2L HFO refrigerants are R-1233zd(Z) and R-1336mzz(E).
What are the advantages and disadvantages of HFO refrigerants?
HFO refrigerants have some advantages and disadvantages that you should consider before using them in your cooling system. Here are some of them:
Advantages
- Environmentally friendly – HFO refrigerants have zero ODP and very low GWP, which means they do not harm the ozone layer or contribute to global warming. They also have short atmospheric lifetimes due to their high reactivity with hydroxyl radicals and chlorine radicals. This means that they do not persist in the environment for long periods of time.
- Energy efficient – HFO refrigerants have similar or better thermodynamic properties than HFCs and CFCs, which means they can provide the same or better cooling performance with less energy consumption. They also have lower pressure drop and lower viscosity than HFCs and CFCs, which means they can reduce the load on the compressor and the piping system.
- Compatible – HFO refrigerants are compatible with most of the existing equipment, materials, and lubricants that are used with HFCs and CFCs. They can also be blended with other refrigerants to create new mixtures with different properties and applications.
Disadvantages
- Flammable – HFO refrigerants are mildly flammable or non-flammable, depending on the type and concentration of HFO. This means that they can pose a fire or explosion risk if they leak or are exposed to ignition sources, such as sparks, flames, or hot surfaces. They also require special handling, storage, and safety measures to prevent accidents and injuries.
- Expensive – HFO refrigerants are more expensive than HFCs and CFCs, due to their limited availability and high production costs. They may also incur additional costs for installation, maintenance, and training, due to their flammability and safety requirements.
- Regulated – HFO refrigerants are subject to various regulations and standards that govern their use, transport, disposal, and reporting. These regulations and standards may vary by country, region, or industry, and may change over time. Users of HFO refrigerants need to comply with these regulations and standards to avoid legal penalties or liabilities.
How do HFO refrigerants compare to other refrigerants?
HFO refrigerants are one of the alternatives to HFCs and CFCs, which are being phased out due to their high ODP and GWP. However, there are other alternatives that have different properties, advantages, and disadvantages. Here are some examples of how HFO refrigerants compare to other refrigerants:
- Hydrocarbons (HCs) – Hydrocarbons are natural refrigerants that consist of hydrogen and carbon atoms, such as propane (R-290), isobutane (R-600a), propylene (R-1270), and ethane (R-170). They have zero ODP and very low GWP, making them environmentally friendly. They also have excellent thermodynamic properties, making them energy efficient. However, they are highly flammable and explosive, making them unsafe for many applications. They also require special equipment, materials, and lubricants that are compatible with hydrocarbons.
- Carbon dioxide (CO2) – Carbon dioxide is a natural refrigerant that consists of one carbon atom and two oxygen atoms (R-744). It has zero ODP and very low GWP, making it environmentally friendly. It also has good thermodynamic properties at low temperatures, making it suitable for low-temperature applications such as supermarket freezers. However, it has high operating pressures and poor thermodynamic properties at high temperatures, making it unsuitable for high-temperature applications such as air conditioning. It also requires special equipment, materials, and lubricants that can withstand high pressures.
- Ammonia (NH3) – Ammonia is a natural refrigerant that consists of one nitrogen atom and three hydrogen atoms (R-717). It has zero ODP and very low GWP, making it environmentally friendly. It also has excellent thermodynamic properties, making it energy efficient. However, it is toxic and flammable, making it hazardous for human health and safety. It also requires special equipment, materials, and lubricants that are compatible with ammonia.
- Hydrofluoroethers (HFEs) – Hydrofluoroethers are synthetic refrigerants that consist of hydrogen, fluorine, carbon, and oxygen atoms. They have zero ODP and low to moderate GWP, making them less harmful than HFCs and CFCs. They also have good thermodynamic properties at high temperatures, making them suitable for high-temperature applications such as air conditioning. However, they are expensive and scarce, due to their limited production and availability. They also require special equipment, materials, and lubricants that are compatible with hydrofluoroethers.
FAQs
Here are some frequently asked questions about HFO refrigerants:
- Are HFO refrigerants safe? – HFO refrigerants are safe if they are used properly and according to the manufacturer’s instructions and safety guidelines. They have lower toxicity than HFCs and CFCs, but they may still cause irritation or harm if inhaled or exposed to skin or eyes. They are mildly flammable or non-flammable depending on the type of HFO but they may still ignite or burn if they leak or are exposed to ignition sources such as sparks flames or hot surfaces. Users of HFO refrigerants need to follow proper handling storage disposal training reporting personal protective equipment fire protection ventilation leak detection emergency response procedures to prevent accidents injuries
