HFO Refrigerants Explained: Chemistry and Applications

Introduction

Hydrofluoroolefins (HFOs) represent the fourth generation of fluoride-based refrigerants. These are unsaturated organic compounds composed of hydrogen, fluorine, and carbon. The key differentiator of HFOs from their predecessors, hydrofluorocarbons (HFCs), is the presence of at least one carbon-carbon double bond in their chemical structure. This double bond makes them more reactive in the atmosphere, leading to a significantly shorter atmospheric lifetime and, consequently, a much lower Global Warming Potential (GWP). HFOs are being developed to replace HFCs in many applications, including automotive air conditioning, and residential and commercial refrigeration and air conditioning.

Chemistry of HFO Refrigerants

The defining feature of HFOs is the carbon-carbon double bond. This makes them olefins (also known as alkenes). The presence of this double bond makes them susceptible to attack by hydroxyl (OH) radicals in the atmosphere, leading to their rapid breakdown. This is in stark contrast to HFCs, which are saturated compounds and are much more stable in the atmosphere. The atmospheric lifetime of HFOs is typically a matter of days, compared to years or even decades for HFCs. This is why HFOs have very low GWPs, often less than 1, while HFCs can have GWPs in the thousands.

Common HFO Refrigerants and their Properties

Refrigerant	Chemical Formula	GWP	Atmospheric Lifetime (days)	Flammability	Applications
R-1234yf	C3H2F4	<1	11	A2L (mildly flammable)	Automotive air conditioning, chillers
R-1234ze(E)	C3H2F4	<1	18	A2L (mildly flammable)	Chillers, heat pumps, aerosols
R-1233zd(E)	C3HCl2F3	1	26	A1 (non-flammable)	Centrifugal chillers, foam blowing agent

Applications of HFO Refrigerants in HVAC

HFO refrigerants are finding increasing use across a wide range of HVAC applications, driven by regulations phasing down the use of high-GWP HFCs.

Automotive Air Conditioning

R-1234yf has become the new standard for automotive air conditioning systems, replacing R-134a. Its low GWP and similar performance characteristics to R-134a have made it a suitable drop-in replacement in many cases. For more information on automotive HVAC components, visit our HVAC Systems & Components page.

Commercial Refrigeration

HFOs and HFO blends are being used in a variety of commercial refrigeration applications, including supermarket display cases and reach-in coolers. These refrigerants offer good energy efficiency and a significant reduction in GWP compared to the HFCs they replace. Explore our range of HVAC Equipment for commercial solutions.

Chillers

R-1233zd(E) is being used in new centrifugal and screw chillers for large commercial buildings. Its non-flammable nature and high efficiency make it an attractive option for this application. R-1234ze(E) is also used in some chiller applications. Find related installation supplies on our Installation Supplies page.

Environmental Impact and Safety Considerations

While HFOs offer a significant environmental benefit due to their low GWP, there are some safety and environmental considerations to be aware of.

Flammability

Many HFO refrigerants, such as R-1234yf and R-1234ze(E), are classified as A2L, meaning they are mildly flammable. This requires careful handling and system design to ensure safe operation. Technicians need to be properly trained on the safe handling of A2L refrigerants. For safety equipment, please refer to our PPE section.

Decomposition Products

One of the atmospheric breakdown products of some HFOs is trifluoroacetic acid (TFA). While TFA is a persistent substance, studies have shown that the amount of TFA produced from the breakdown of HFO refrigerants is not expected to have a significant impact on the environment.

FAQ

1. What is the main difference between HFO and HFC refrigerants?

The main difference is the presence of a carbon-carbon double bond in HFOs, which makes them more reactive in the atmosphere and gives them a much lower GWP than HFCs.

2. Are HFO refrigerants flammable?

Some HFO refrigerants are classified as A2L, meaning they are mildly flammable. However, not all HFOs are flammable. For example, R-1233zd(E) is non-flammable (A1).

3. Can HFOs be used as a drop-in replacement for HFCs?

In some cases, HFOs can be used as a near drop-in replacement for HFCs, but this is not always the case. It is important to consult the equipment manufacturer\'s recommendations before retrofitting a system with an HFO refrigerant.

4. What are the safety precautions for handling HFO refrigerants?

Technicians should be properly trained on the safe handling of A2L refrigerants, which includes proper ventilation, use of personal protective equipment, and use of tools and equipment designed for use with flammable refrigerants.

5. What is the environmental impact of HFO refrigerants?

HFOs have a very low GWP, which is a significant environmental benefit. However, there are some concerns about the atmospheric breakdown products of HFOs, such as TFA. Studies have shown that the amount of TFA produced is not expected to have a significant impact on the environment.