8. Current and Possible Future Applications of HFOs and natural refrigerants

The use of HFOs is increasing, and new types are continually being developed, both pure HFOs and new blends. The WMO noted in their 2022 report that since its last publication in 2018, one new HFO substance (HFO-1132(E)) and 23 unique refrigerant blends had become designated refrigerants. Low-GWP alternatives exist for all refrigeration, air conditioning and heat pump (RACHP) appliances.

The sectors presented this section are chosen with this project's end-of-life scope in mind, and the sector descriptions are largely built on those applied by the Ozone Secretariat’s Technical Options Committees assessment reports.

Numerous aspects impact the choice of refrigerant, including:

Environmental legal obligations
Safety requirements
Energy efficiency
Materials compatibility
Component availability
Refrigerant availability
Technician competence
System Architecture

8.1 Vehicle Air-Conditioning and Transport Refrigeration

Mobile AC for vehicles

Before the introduction of new low-GWP alternatives, HFC-134a was predominantly used in air-conditioning systems in vehicles. After implementing the MAC Directive (see section 7), HFO-1234yf has been widely adopted as the low GWP alternative in new passenger vehicles in Europe.

European Commission (2014)

Another low-GWP alternative for vehicle AC is R-744; R-744 is increasingly used in fully electric passenger cars and buses.

Ozone Secretariat (2018b).

Transport refrigeration

Transport refrigeration entails refrigeration units for trucks, trailers, light commercial vehicles, and marine and air containers that transport temperature-sensitive products such as foods and pharmaceuticals. Some specific requirements for refrigerants to be suitable for transport refrigeration include shock, vibration, corrosion, and broad operating conditions.

Ozone Secretariat (2018b).

Many newer refrigerated trucks and trailers in Europe employ R-452A; an HFC/HFO blend with a GWP of 2140, significantly lower than R-404A (GWP 3922). Projections predict that R-744 and R290 will be the refrigerants of choice for vehicle refrigeration in the future. Small units utilising these refrigerants are already becoming available on the market.

Ozone Secretariat (2022a)

One challenge for these new alternatives is that R-744 is less efficient at moderate or high ambient temperatures.

Ozone Secretariat (2018b)

8.2 Sealed Domestic and Commercial Refrigeration Appliances and Heat Pump Tumble Dryers

All the devices in the categories 'Sealed domestic and commercial refrigeration appliances’ and ‘Heat Pump Tumble Dryers’ are plug-in, stand-alone and have a factory-sealed refrigeration system. Domestic appliances include refrigerators, freezers and heat pump tumble dryers. Commercial appliances include, for example, stand-alone display cases, beverage coolers, vending machines and ice machines found in supermarkets, restaurants, etc. Most domestic refrigerators and freezers utilise HC-600a. For stand-alone commercial appliances, there is an increase in devices using HC-290. In larger retail refrigeration charge systems, R-744 is also used. However, hydrocarbons are expected to be used primarily long-term after the revision of safety standards in 2019 and the additional costs due to greater material use to protect against the higher pressure level.

No current, significant use of HFOs has been identified in these product categories. HFO-1234ze, HFO-1234yf and several blends are suitable refrigerants for these appliances since they have similar properties to HFC-134a, the previous dominant refrigerant in this category. One study has successfully tested R-450A as a drop-in replacement for HFC-134a in domestic heat pump tumble dryers.

Gataric & Lorbek (2021)

Still, they are unlikely to be deployed on a larger scale. For pure HFOs, this is mainly due to conversion costs.

Ozone Secretariat (2022a)

In the EU, it has been prohibited since 2015 to put new domestic refrigerators and freezers on the market that contain HFCs with a GWP of 150 or more. Since January 1^st, 2020, it has been prohibited to put refrigerators and freezers for commercial use on the market if they contain HFCs with a GWP of 2500 or more. January 1^st, 2022, this limit was lowered to 150 GWP.

Regulation (EU) No. 517/2014

8.3 Larger Refrigeration and Air Conditioning Equipment

The category ‘Larger stationary refrigeration and AC’ is characterised by the refrigerant systems being filled, refilled, and recovered on site. Refrigerant charges vary from a few kilos to several tonnes.

Food retail and food service refrigeration

Three types of equipment are used in food retail and food service refrigeration : stand-alone equipment (described above), condensing units, and centralised and distributed systems. Previously, HCFC-22 and, later, HFC-134a and R-404A have been used. There have been technology developments for equipment using low-GWP refrigerants, and low-GWP alternatives are available:

R744 is increasingly used in retail food systems in cascaded systems with another refrigerant (R-450A, R513A, HFO-1234ze, R-717, HC-290, etc.)
Some transcritical systems are using only R744.
Several new HFO/HFC blends based on HFO-1234yf, HFO-1234ze(E) and HFC-32 can be used and are in use in several different equipment types.
HC-290 is in use in smaller capacity systems.

Considerations related to energy efficiency are essential when choosing refrigerants since these installations typically are in permanent use.

Regulation (EU) No. 517/2014

In the EU, stationary refrigeration equipment that contains or whose functioning relies upon HFCs with a GWP of 2500 or more, has been prohibited from being placed on the market since 1 January 2020. Exemptions are equipment intended to cool products to below -50 °C. Multipack centralised refrigeration systems for commercial use with a capacity of at least 40 kW that contains or rely on fluorinated GHGs with a GWP of 150 or more to function have been prohibited from being placed on the market since the 1^st of January 2022, with an exception for fluorinated GHGs used in the primary refrigerant circuit of cascade systems, they may have a GWP of less than 1500.

Regulation (EU) No. 517/2014

Industrial refrigeration

Industrial refrigeration is used in several industries, including food processing, cold storage, leisure applications, and process refrigeration. Most industrial refrigerant systems with a capacity from 300 kW to over 100 MW use R-717 as the refrigerant, but there are also newer industrial transcritical systems with R-744 refrigerant, especially in milder climates. HFO blends are also used in smaller industrial systems but to a lesser extent.

There are numerous different refrigerant combinations used for cold storage systems:

In cold and mild climates, R-744 trans-critical systems are used.
In warmer climates, R-717 is used.
Cascade systems using a combination of R-744 and R-717 are also in use.
HFC/HFO blends
HFC-23 has been widely used in temperature-sensitive storage installations, such as pharmaceuticals. Cascade systems using a combination of HC-170 and either R-717 or HC-290 have been used as replacements for HFC-23 instalments.
Regulation (EU) No. 517/2014

Industrial heat pumps

Industrial high-temperature heat pumps up to 95 °C and heat pumps used for district heating also use R-717. HFOs, namely HFO-1234ze(E), are a suitable refrigerant for industrial heat pumps as an alternative to HFC-134a, and several market-available options exist. For temperatures above 100 °C (steam production), R-718 and HCs are both viable and commercially available.

Building cooling systems

The category ‘Building cooling systems’ refers to AC systems in commercial buildings for heating and cooling, also called large HVAC. Different air- and water-cooled chiller systems using HFC refrigerants are most frequently used. There are several market-available low-GWP alternatives for new chiller equipment. Which refrigerants are suitable for which equipment depends on whether low, medium, or high-pressure refrigerants are needed. HFO-1233zd is a low-pressure refrigerant, whereas HFO-1233zd(E) and HFO-1234yf are medium-pressure refrigerants. HFO-1233zd(E) is expected to be more widely adopted in products that need medium-pressure refrigerants.

Natural refrigerants are also used in chillers, including R-717- R-718 and R-744, but are less common.

It is possible to change refrigerants in existing equipment by replacing them with drop-in blends with the same safety classification and similar energy efficiency, cooling capacity, discharge rates and volumetric flow rates. The HCFO/HFO blend R-470A has similar properties to R-410A and is therefore considered a potentially suitable drop-in for R-410A. Another option is to retrofit the systems. HFOs are considered especially promising in this category due to their lower flammability; flammability is a severe problem when considering building safety codes.

Ozone Secretariat (2022a)

8.4 Domestic Air-Conditioners & Heat Pumps

ACs and heat pumps of 1 kW–1,100 kW comprise most of the market of domestic air-conditioners and heat pumps. They are typically used in domestic housing, offices, etc. Historically, first HFCF-22 and later R-410A have been the refrigerant of choice for this type of equipment, followed by R-32.

Table 3 AC Types and suitable refrigerants

Type		Primary configuration	Capacity range (kW)	Viable low-GWP options
Small self-contained (SSC)	Window	Small self-contained	1–10	HFO-1234yf, HC-290, R-744, HC-1270.
	Movable	Small self-contained	1–10
	Through-the-wall	Small self-contained	1–10
	Packaged terminal	Small self-contained	1–10
Non-ducted single split		Non-ducted split	2–30	HFO-1234yf, HC-1270 (≤20 kW), HC-290 (≤20 kW).
Ducted residential split		Ducted split	4–17.5	HFO-1234yf, HC-1270 (≤20 kW), HC-290 (≤20 kW).
Ducted commercial split		Ducted split	10–1,100	HFO-1234yf, HC-1270 (≤20 kW), HC-290 (≤20 kW).
Multi-split		Non-ducted and ducted split	4–300	HFO-1234yf HC-1270 (≤15 kW), HC-290 (≤20 kW).
Packaged ducted		Ducted self-contained	5–1,100	HFO-1234yf, R-744, HC-1270 (≤20 kW), HC-290 (≤20 kW).

In addition to the low-GWP options listed in the right column, numerous blends are also available and suitable for AC products. There are also AC systems using R-744 in capacities ranging from 3 to 300 kW, mainly available in Northern Europe.

Ozone Secretariat (2022a)

In the EU, movable room AC equipment that contains HFCs with a GWP of 150 or more has been prohibited from being placed on the market since the 1^st of January 2022. From 2025, it will be prohibited to place any single split AC systems containing less than 3 kg of fluorinated GHGs on the market if they contain or rely on fluorinated GHGs with a GWP of 750 or more to function.

Regulation (EU) No. 517/2014

8.5 Foam in Buildings and Construction

Foam-blowing agents are widely used in buildings and construction. Foams used for building and construction have long lifetimes, often 50 years or longer.

European Commission (2022a)

Foams are either blown on-site or fabricated into products at the manufacturer. No single drop-in replacement exists for the HFC and HCFC foam-blowing agents, but different alternatives are available for all appliances. In the EU, placing extruded polystyrene (XPS) foams containing HFCs with a GWP of 150 on the market has been prohibited since January 1^st, 2020. The same prohibition was implemented for other foams January 1^st, 2023.

Regulation (EU) No. 517/2014

Hydrocarbons, including cyclopentane, pentane, isopentane, HFOs/HCFOs and water, are all used as foam-blowing agents. In building and construction, foam-blowing agents are used in the following products:

Ozone Secretariat (2023)

Table 4

Product	Commercially available low-GWP no-ODP alternatives	Comment
Extruded polystyrene (XPS) for insulation	HFOs/HFCOs, HCs and water	Due to flammability concerns, the hydrocarbon isobutane is only used as a co-blowing agent. HFO-1233zd(E) is anticipated to be the primary replacement for HFC-134a because they have similar properties.
PU spray foams	HFO-1233zd(E) and HFO-1336mzz(Z), HCs, Water	Hydrocarbons are not widely used because of flammability concerns.
PU panels	HFOs/HFCOs, HCs and water	Hydrocarbons are currently the primary foam-blowing agent used in PU panels. In the future, HFO/HCFO and hydrocarbon blends might be considered to increase thermal performance.
PU board stock	HFOs/HFCOs, HCs and water	Hydrocarbons are currently the primary foam-blowing agent used in PU board stock. In the future, HFO/HCFO and hydrocarbon blends might be considered to increase thermal performance.
PU in-situ and block foams	HFOs/HFCOs, HCs and water	Hydrocarbons are most often used in PU in-situ and block foams. In the future, HFO/HCFO and hydrocarbon blends might be considered to increase thermal performance.

8.6 Foams in Products

Refrigeration foam insulation

Foams are used as refrigeration foam insulation in domestic appliances such as refrigerators and freezers, commercial refrigeration, and refrigerated transport. HFOs, HCFOs, Hydrocarbons and water are all used as foam-blowing agents. HFO-1233zd(E) and HFO-1336mzz(Z) are both in use. Most emerging technologies in the appliance sector are based on HFOs and HCFOs. Many manufacturers use HFOs or HCFOs as co-blowing agents with pentane.

Ozone Secretariat (2023)

Polyurethane (PU) integral skin and other non-insulating foams

Polyurethane (PU) integral skin and other non-insulating foams are used in several appliances, including automotive parts and furniture. Water and hydrocarbons are generally utilised as foam-blowing agents. Some new emerging technologies are based on HFOs or HCFOs. HFO-1233zd(E) and HFO-1336mzz(Z) are used, but the prices for HFOs and HCFOs are significantly higher than hydrocarbons and water. It is as such common to blend them with hydrocarbons to lower the costs.

Ozone Secretariat (2023)

8.7 Aerosol Propellants

Aerosols have many different applications. Aerosols are often divided into the categories of consumer aerosols, technical aerosols, and medical aerosols. Suitable liquefied gas propellants include HCFCs, HFCs, HFOs, Hydrocarbons and dimethyl ethers. Hydrocarbons and dimethyl ethers are predominantly used in the consumer market. HFCs, namely HFC-134a, are still used in medical applications and for applications where non-flammable propellants are needed. HFOs are more expensive than hydrocarbons and HFCs, but are in use.

Ozone Secretariat (2022b)

HFO-1234ze(E) is used in consumer aerosols, and research is being conducted on the safety of HFO-1234ze(E) as an alternative for use in Metered Dose Inhalers (MDIs).

European Commission (2022a)

Since January 1^st, 2018, technical aerosols containing HFCs with a GWP higher than 150 were no longer allowed to enter the European market. Aerosols needed to meet national safety standards or for medical applications are exempt from the prohibition.

Regulation (EU) No. 517/2014

8.8 Fire Suppression

HFOs are not yet in use for fire suppression. However, studies show that HFO-1336mzz(E) has application potential.

Zhang et al (2020)