Evolution of new refrigerants and applications

INTRODUCTION: The purpose of this technical article is to understand the importance of new available refrigerants, and applications. In this paper, the low or ultra-low GWP refrigerants like hydro-fluoro-olefins HFO / HFO blends, HC, and Natural Refrigerants are considered as environmentally friendly next-generation refrigerants.
Early invention – inorganic compounds, today these are still used in many refrigeration, Air conditioning, and heat pump applications as refrigerants such as ammonia (NH3), water (H2O), carbon dioxide (CO2), and sulfur dioxide (SO2). Synthetic refrigerants have been used in refrigeration systems since the creation of CFCs and HCFCs in 1929.
Refrigeration and air conditioning play a vital role in domestic, commercial, and industrial applications. They have a great impact on our day-to-day life. They have also contributed to the world’s major environmental issues like global warming and climate change. The development of the refrigerants used in them, from the days when refrigeration was not known to the present day is very interesting. The development of different refrigerants over time took place based on safety, durability and environmental impact issues. Now, there has been a lot of talk about climate change and global warming.
The first regulation concerning the depletion of the ozone layer was the Montreal Protocol adopted on 16th Sep 1987. The result was that the scientific assessment of ozone depletion in 2014 confirms that the ozone layer is healing, thanks to actions taken by Parties under the Montreal Protocol. It means the Ozone Depletion Potential matter is resolved but the Global Warming potential is highlighted due to increase of global temperature and climate change.
Then, the Kigali Amendment, adopted in 2016, aims to phase down hydrofluorocarbons (HFCs), potent greenhouse gases that contribute to global warming. As of 1st July 2024, 160 countries have ratified the Kigali amendment. Under the Amendment, all countries will gradually phase down HFCs by more than 80 per cent over the next 30 years and replace them with more planet-friendly alternatives.
The scientists and engineers carried out the research and development to establish the next generation refrigerants including the safety that is the most important factor. The recent Scientific Assessment Report estimates that Kigali will reduce future global average warming in 2100 due to HFCs from a baseline of 0.3 °C – 0.5 °C to less than 0.1 °C.
Hydrocarbons are naturally occurring and made only from hydrogen and carbon. Let’s see the current availability of new refrigerants compared to existing HFC refrigerants for low, medium, and high-pressure applications of compressors. We need to choose the new refrigerants based on the environmental effect (GWP), safety, performance (COP), availability, and serviceability.
The three main flammability classifications are class 1 – for refrigerants that do not propagate a flame when tested as per the standard; class 2 – for refrigerants of lower flammability; and class 3 – for highly flammable refrigerants.
The classification of refrigerants are as follows:
The demand of Natural Refrigerants like Ammonia and Carbon dioxide as well as HCs are increasing. A2L refrigerants are slightly flammable than A2 and A3 is highly flammable. B1 & B2 represents toxicity. Mostly, new refrigerants belong to A2L, we should have a serious look at the design and installation of any indoor/outdoor unit, piping, valves, and mechanical room to avoid any accident, as it pertains to the limit of refrigerant charge, sensors, and exhaust according to available standards and local codes.
Ammonia is widely used in the food processing, cold storage, and pharmaceutical industries. However, local permitting authorities may restrict the use of ammonia due to its toxicity and flammability. It has pungent smell. System design for the best system COP may result in high cost, particularly when considering necessary items to ensure safety. Ammonia belongs to B2 category makes it suitable only for indirect chiller systems.
Carbon Dioxide belongs to the AI group, a greenhouse gas, and is very energy efficient but operates at very high pressure. CO2 and its high energy content, which continues to scale at greater temperatures, can be reclaimed, increasing overall system efficiency. From an environmental perspective, CO2 is a very attractive refrigerant with zero ODP and a GWP of 1 Carbon dioxide sees extensive use in large-scale refrigeration systems like marine refrigeration systems.
Hydrocarbons (HC) HC refrigerants have an Ozone depletion potential (ODP) of 0 and a global warming potential (GWP) is 3. Typical hydrocarbon refrigerants for Line refrigerators and freezers are Propane (R-290) or Isobutane (R-600a) but highly flammable belongs to the A3 category. It requires additional safety measures.
However, there’s been a push in recent years to explore other uses for R-290, and ASHRAE has proposed increasing its charge limit to either 300 grams or 500 grams, depending on the application.
ASHRAE Standard 34 shows that Application for Human Comfort stipulates that Group A2, A3, B1, B2, and B3 refrigerants shall not be used in high-probability systems for human comfort. Higher Flammability Refrigerants states that Group A3 refrigerants shall not be used except where approved by the authority having local jurisdiction.
Refrigerants listed as A2L in ASHRAE 34 are listed as Class 2 in the International Mechanical Code.
When we go deep then we see category A2 is divided into A2L and A2 groups. The A2L subgroup, as categorized by ASHRAE Standard 34, are a class of refrigerants that have lower flammability (flame propagation speed is less than 10 cm/s) compared to A2.
HFO refers to the chemical composition of the refrigerant. HydroFluoroOlefin indicates that the refrigerant is comprised of Hydrogen, Fluorine, and Carbon and that there is at least one unsaturated double bond between two carbons (olefin structure). A blend of an HFO with another type of refrigerant is typically combined with a slash HFO blend i.e. next-generation refrigerants compared to existing HFC refrigerants (R-134a, R-407c, and R-410a) i.e., high GWP:
R-1234yf
R1234yf is more environmentally friendly. It has 4 GWP compared to R-134 a 1300 GWP. R1234yf can be used as a long-term environmentally friendly solution in mobile air-conditioning systems. The safety kit is also available to detect the leakage. Technicians need to take the relevant safety measures for the correct transport, storage, and handling of flammable gas.
R-32
The GWP of R32 is 675 while R-410 has 2,088 GWP. EPA based on the Kigali amendment bans CFCs with GWP above 700; this stops new production or importation of R-410a Units by Jan 01, 2025. Besides, the EPA based on the Montreal Protocol stopped production and importation in 1996 for R12 machines and 2010 for R22 machines.
R32 only has one molecule in its formation, its saturated liquid and vapor temperatures are the same. R-32 is a colorless and odorless, mildly flammable gas (A2L). However, there is a slight chance of the smallest fully enclosed premises with total leakage in the evaporator unit.
R-32 is more efficient than R-410a. R-32 is available and requires less quantity than R-410a. R-32 pressure is high compared to R-410a and manufacturers mainly use it in Split Units or VRF. The outdoor unit should be installed in a shaded area especially at high ambient countries. Flush with Nitrogen and proper vacuum requires, and no air should be inside the pipe.
There is a chance of any damage the indoor unit installed in at confined space with a small amount of room volume. But it requires oxygen and constant sources to ignite like hot wire, open flames, etc.
R-32 is heavier than air, it goes down to the floor and may accumulate as well as have lower velocity at ground level then it may favor the formation of the fire but requires a constant high-power source is still required.
R-452B / R-454B
R452B is a mixture of HFC and HFO, with a glide temperature of 1.2 K. Its GWP is 676. Further, R452B has a safety classification of A2L and lower saturation pressure than R410A and R32.
R454B has 466 GWP compared to R-410 has 2,088 GWP. R-454B is mildly flammable gas (A2L) and colorless. Many manufacturers are using R454B refrigerant. It provides easy conversion with minimal changes from the R-410a design. Like R-410A, R-454B is a near azeotrope and so has minimal glide.
Manufacturers use R454B in Residential Light Commercial, Chillers and Heat Pumps. R454B extends cooling and heating capabilities at low ambient temperatures producing higher leaving hot water temperatures. R454B has wider operating maps and compressors, i.e. more reliable. R454B, to comply with future regulations and reduce their carbon footprint.
R-513A
R513A is a medium-pressure, non-flammable. The GWP of R-514A is 573. They have been assigned an A1 safety classification under ASHRAE 34. It may be an alternative to R-410a for new medium and high-temperature systems. It may use in screw and centrifugal chillers.
It is a direct drop-in replacement for R-134a in existing commercial and industrial medium and high-temperature refrigeration equipment that uses positive displacement compressors and direct expansion systems. It is compatible with POE synthetic oils. It is compatible with the equipment, components, lubricant, and joints of an existing R-134a system.
R-514A
ASHRAE 34 class R514A as a B1 category refrigerant, meaning that it is not flammable. It has a low pressure, non-ozone depleting, low global warming potential (GWP) hydrofluoroolefin (HFO) based replacement for R-123. It is suitable for new and retrofit systems, offering an optimal balance of properties, including high energy efficiency and environmental sustainability.
An Azeotrope with zero glides is a low GWP HFO-based refrigerant developed to replace R-123 in low-pressure centrifugal chillers for commercial and industrial applications. The application may be screw and centrifugal chillers.
R-1234ze
R-1234ze is known as a “next-gen” refrigerant & classified as HFO. It has category is A2L and not designed for retrofit projects. While the fact R1234ze has an ultra-low value GWP value is 1 vs 1300 of the R134a, it also results in very efficient chiller operations. This is pure fluid and having zero glide. The lubricant oil is POE Oil. It replaces mainly R134a refrigerant.
The application is air-cooled and water-cooled screw chillers as well as water-cooled centrifugal chillers. Besides, it can be used in medium-temperature commercial refrigeration and heat pumps. This refrigerant has a future choice within a stringent environmental regulation.
R-1233zd
R-1233zd is known as a “next-gen” refrigerant & classified as HFO. It has ultra-low value GWP value is 1. R1233zd is ideal for low-pressure centrifugal chillers which are common in cooling systems for large buildings. Besides, it has no temperature glide.
Refrigerant R1233zd(E) is classified as a fully safe refrigerant (ASHRAE Class A1). The composition of this refrigerant is a single component. R-1233zd is a new and widely accepted refrigerant for high-capacity mainly centrifugal chillers for its attractive properties and mainly to replace R123 refrigerant.
The initial cost of new refrigerants is typically high, but the cost tends to decrease with time due to production process improvements and economies of scale. The total Life Cycle Cost of a system has become increasingly important in recent years as the cost of the system to acquire, install, operational cost, and maintain gained focus.
CONCLUSION: HFCs have high global warming potential (GWP) and trap heat in our atmosphere which contribute to global warming. Thus, they are ultimately bad for the environment. Ultimately, the Kigali amendment timeline must be followed for respective countries. In addition, we need to follow the new design standards (especially A2L & A3), take safety precautions, select high-efficiency equipment, and follow ASHRAE Standards as well as local codes.