Eco-Friendly Refrigerants

Eco-Friendly Refrigerants

What is Refrigerant?

Refrigerants are used to cool specific spaces. Generally, they are in liquid or gaseous form. There are different types of refrigerants intended to take heat from a specific area and deliver it to other places that need it. Refrigerant used in various equipment such as air conditioners and chillers. They typically use the thermodynamic phenomenon of phase change to convert gases to liquids and vice versa. Although these refrigerants are very useful, they are believed to be a major contributor to global warming. However, as technology progressed, environmentally friendly refrigerants were introduced.

Fig.1 Refrigerants

Selection of Refrigerant:

The thermodynamic efficiency of a refrigeration system depends primarily on its operating temperature. However, important practical aspects such as system design, size, acquisition and operating costs, safety, reliability and serviceability are highly dependent on the type of refrigerant chosen for a particular application. 

Due to various environmental issues such as ozone depletion and global warming and the variety of refrigerants used, the selection of a suitable refrigerant has become one of the most important issues in recent times.

Fig.2 Selection Criteria

Environmental and safety properties:

The environmental friendliness of refrigerants is an important factor in determining the usefulness of a particular refrigerant. Important environmental and safety characteristics include: 

Ozone Depletion Potential (ODP): The ODP of refrigerants should be zero, according to the Montreal protocol. Because ODP is primarily determined by the presence of chlorine or bromine in the molecules, refrigerants containing either chlorine or bromine are prohibited under the new regulations.
Global Warming Potential (GWP): Refrigerants directly contribute to global warming when they are released into the atmosphere. indirect contribution based on energy use, including that of the compressors (CO2 produced by power stations).To reduce the issue of global warming, refrigerants should have a low GWP rating.
The Total Equivalent Warming Index (TEWI): which considers refrigerants direct and indirect effects on global warming. Low TEWI refrigerants are obviously favored from the perspective of reducing global warming.
Toxicity: Refrigeration system refrigerants should ideally be non-toxic. Toxicity is a relative term that only has meaning when the level of concentration and duration of exposure required to cause harmful effects are specified.
Flammability: The refrigerants should be non-flammable and non-explosive if possible. To avoid accidents with flammable refrigerants, special precautions should be taken.
Chemical stability: Refrigerants must be chemically stable while inside the refrigeration system.

Ease of Leak Detection: In the event of leakage of refrigerant from the system, it should be easy to detect leaks.

The major categories of refrigerants are:

Chlorofluorocarbons (CFCs):

CFCs are chlorine, fluorine, and carbon atom compounds that are used to make aerosol sprays, blowing agents for foams and packing materials, solvents, and refrigerants. They are regarded non-eco-friendly refrigerant gases because to their high ODP (Ozone Depletion Potential) and GWP (Global Warming Potential).

Examples include R11, R12, R113, R114, and R115.

Fig.3 R-12 (CFC) 

Hydrochlorofluorocarbons (HCFCs):

HCFCs are chemical compounds made up of hydrogen, chlorine, fluorine, and carbon atoms. HCFC refrigerants have a medium to high GWP and are commonly utilized in refrigeration and air conditioning systems. Once again, these are not ecologically friendly refrigerant gases that have been phased out or are being phased out in most nations.

For instance, R22, R141b, R123.

Fig.4 R-141B (HCFC)

Hydrofluorocarbons (HFCs):

HFCs, a fluorocarbon mixture, have no ODP and a moderate to high GWP, making them a greener option to CFCs and HCFCs. HFCs are used in foam making, refrigeration, and other operations to replace CFCs. HFCs may contribute to global warming, but they have no direct effect on the ozone layer.

Examples are R32, R134a, and R152a.

Fig.5 R-134a (HFC)

Hydrofluoro-olefins (HFOs):

HFOs are made up of the same three atoms as HFCs, but they are unsaturated organic compounds, hence the suffix "olefin. "They have a double bond between two carbon atoms with their parent hydrocarbon. Because of the double bond, the molecules are less stable and degrade swiftly in the atmosphere—in days rather than years or decades for HFCs. Because they have no ODP and a relatively low GWP, HFO refrigerants are claimed to be the most environmentally benign refrigerants currently available.R449A, R454C, R513A, R1234yf, R1234ze, R1233zd, R1336mzz are HFO refrigerants found in commercial and industrial air conditioning and refrigeration systems, water chillers, vehicles, portable air conditioners, and heat pumps.

Fig.5 R1234yf, R1234ze (HFO)

Inorganic refrigerants:

Carbon Dioxide: There is no ODP or GWP. Non-flammable and non-toxic. Low-cost and widely available. Its high operating pressure allows for system size and weight reduction potential.

Ammonia: ODP and GWP are both zero. Excellent thermodynamic properties: low molecular mass, high latent heat, high vapor density, and excellent heat transfer properties. High critical temperature (132 degrees Celsius): highly efficient cycles at high condensing temperatures. Its odor causes leaks to be detected and repaired before they reach dangerous concentrations. Price is Reasonably Low.

Water: ODP and GWP are both zero. In an absorption system, water is used as a refrigerant. New developing technology has made room for it to be used in compression cycles as well. However, higher than normal working pressure in the system can play a role in the limited use of water as a refrigerant.

Table.1 Refrigerant Properties.

Table.2 ODP and GWP of different Refrigerants.  

Graph.1 Overall review of GWP of Refrigerants 

Montreal Protocol:

The Montreal Protocol is a historic international agreement aimed at preserving the stratospheric ozone layer.

The Montreal Protocol, officially the Protocol on Substances that Deplete the Ozone Layer, is a treaty signed on September 16, 1987, in Montreal by 25 states; it presently has 168 signatories.

The protocol-imposed restrictions on the manufacturing of chlorofluorocarbons (CFCs), which are organic molecules containing carbon, chlorine, and fluorine atoms. CFCs are highly efficient refrigerants developed in response to the urgent need to eliminate harmful and combustible compounds.

The protocol calculates the ozone-depleting potential, or ODP, of any substance in relation to an equal quantity of CCl3F, or CFC-11, which is assigned a value of 1.0.

Table.3A Refrigerants phase out period

Table.3B Reduction in consumption for Developed and Developing Countries

Application of New Eco-friendly Refrigerants:

Benefits of Eco-friendly refrigerants:

Recycling or disposal after use in refrigeration systems is relatively easier than CFCs, HCFCs and HFCs.

In general, these gases are more energy efficient than F-gas. The chemical industry has not patented these refrigerants, which are less expensive than HFCs.

These gases are not hazardous to the environment and can be handled with care. 

These gases are produced as by-products of other processes. If you can set up a good distribution structure, it will be easier to make them available out of the box.

Conclusion:

The environmental friendliness of a refrigerant can be measured by its ODP (Ozone Depletion Potential) and GWP (Global Warming Potential).

CFCs, HCFCs, and HFCs are chemically synthesized and do not occur as natural compounds. Moderate to high ODPs and GWPs are being phased out under the Montreal Protocol (1987) because they are extremely harmful to the environment.

HFO is a synthetically produced unsaturated HFC with no ODP and low GWP, making it the greenest refrigerant gas with the least negative environmental impact.

Natural refrigerant he has zero ODP and very low GWP, making it an ideal replacement for CFC, HFC and HCFC. They are naturally occurring substances such as CO2, ammonia, water and air. They may be hydrocarbons. propane, isobutene, propene or propylene.

References:

1.HCFC phase out schedule and baselines, Montreal Protocol, United Nation Environment Programme (UNEP).

2.Linn Mikaela Persson, Åsa Persson, Måns Nilsson, Multilateral Environmental Agreements on the Ground – Lessons from Supporting Implementation of the Montreal Protocol, ResearchGate Jan 2007.

3.Vijayan Gurumurthy Iyer, Nikos E Mastorakis, Experimental Investigations on Eco-Friendly Refrigeration and Air Conditioning Systems, ResearchGate, Jan 2006.

4.https://www.allrefrigerants.com/blog/advantages-of-eco-friendly-refrigerant-gases.

5.Dr. Shivaprakash Bhagwatrao Barve, Eco-Friendly Refrigerants, ResearchGate, Oct 2013.

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Authors:

1. Jaydeep Patil
2. Rohit Patil
3. Gokarna Lele
4. Abhishek Kumbhar
5. Rohit Bele
6. Kedar Basutkar