4.13 Carbon: Alternative Refrigerants

Author: Emily Robins

ABSTRACT: Although carbon dioxide (CO2) emissions are the primary cause of the greenhouse effect, compounds other than CO2 can act as powerful greenhouse gases as well. This includes refrigerants that leak from air conditioners and refrigeration systems in homes, businesses, and industries. Though the volume of refrigerants released into the atmosphere is far less than the volume of CO2, they are a significant concern due to their immensely powerful global warming potential.



Refrigerants are substances that are used for cooling systems in various equipment such as air conditioners, refrigerators, and freezers. There are five categories of refrigerants; chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs), hydrofluoroolefins (HFOs) and natural refrigerants (Anthon, 2017).

Developed in 1928, CFCs became the first popularized synthetic refrigerant. It is composed of carbon, chlorine, and fluorine. With an atmospheric lifespan of 55-140 years depending on the compound, CFCs not only leak greenhouse gases but destroy the ozone as well (Elkins,1999). By 1996 it became illegal for all developed countries to produce CFCs and by 2010 they were banned worldwide (Anthon, 2017).

HCFCs were produced as a replacement. HCFCs have a structure very similar to CFCs, with carbon, chlorine, and fluorine, but with the addition of hydrogen. It was claimed that HCFCs were a good alternative because they were less ozone-depleting, did not contribute to global warming as much, and had a considerably shorter atmospheric lifespan of about 13 years (Carbajal & Kanter, 2009). Yet they still contained chlorine which is the element that was damaging the ozone. HCFCs began to be phased out in 2004 yet they will not be completely eliminated until 2030 (Anthon, 2017).

HFCs were developed as the best refrigerant alternative because of their shorter atmospheric lifespan and their lack of chlorine, so they pose no threat to the ozone. However, they are a more powerful greenhouse gas than both CFCs and HCFCs. HFCs, have a 20-year global warming potential of 3,830, compared to carbon dioxide at 1 (Carbajal & Kanter, 2009). Still the most commonly used refrigerant today, they began to be phased out as of 2019 (Anthon, 2017).

HFOs are the next emerging type of synthetic refrigerant. Though not widely used at this time, they are beginning to grow. Like HFCs, HFOs are composed of hydrogen, fluorine, and carbon. The only chemical difference between the two are that HFOs have one double bond between carbon molecules (Carbajal & Kanter, 2009). HFOs pose no risk to the ozone and are a minimally potent greenhouse gas. However, there are several other concerns with them. HFOs are flammable so they are often being combined with HFCs to create non-flammable blends, which greatly increase its global warming potential. When certain HFOs break down in the atmosphere it produces a substance called trifluoroacetic acid (TFA), which in high enough concentrations is toxic to aquatic ecosystems. While TFA are a common byproduct when HFCs break down, HFOs produce 4 to 5 times as much. This means that if HFOs become the refrigerants of choice, the concentration of TFA in freshwater bodies around the world could increase dramatically with unknown effects on ecosystems and human health. Lastly, certain HFOs are made using HCFCs despite its impacts on the ozone, and the substances that are released into the atmosphere as a result of this production are still unknown (Carbajal & Kanter, 2009).

Natural refrigerants are comprised of compounds that can be found naturally. They pose no significant threat to the ozone and have a drastically lower global warming potential than synthetic refrigerants. The most common include ammonia, hydrocarbons, and carbon dioxide. Ammonia is currently the most commonly used natural refrigerant (Carbajal & Kanter, 2009). On average, ammonia refrigeration systems cost 10-20% less to install and are 3-10% more energy efficient. They are efficient for low temperature applications, easy to maintain and operate, and have a low operating pressure, although they are toxic and corrosive to copper, brass and bronze. Certain hydrocarbons are very efficient refrigerants (Navarro, Eibisch, & Schneider, 2019). Hydrocarbons include propane, propylene, and isobutane. Although they do have flammable properties, they are best used for smaller commercial equipment (Carbajal & Kanter, 2009). Despite being known as a notorious greenhouse gas, carbon dioxide has very positive characteristics as a refrigerant. It does not deplete the ozone layer and has a global warming potential of 1 compared to thousands for synthetic refrigerants. It has a high temperature fluid for heat recovery, is low maintenance, non-toxic and non-corrosive, as well as its properties allow for use in more compact systems like in vehicles, although it has a low critical temperature so it is not as suited for cooling (Navarro, Eibisch, & Schneider, 2019).

There are a number of potential reasons why more people are not using natural refrigerants, first of all, unlike synthetic refrigerants there is no “drop in” option, meaning that you would need to replace the entire system which is a larger upfront cost (Carbajal & Kanter, 2009). Yet, the largest factor is awareness. HFCs are still the most commonly used refrigerant despite their global warming impacts and now money, resources, and marketing is going towards HFOs as being the best eco-friendly option without people being properly educated on the impacts it causes to the environment and the availability of natural refrigerants (Carbajal & Kanter, 2009). Natural refrigerants are the best available alternative and HFO technology will only delay their development.


Anthon, J. (2017, June 5) PDF. Washington; Bonneville Power Administration. https://www.bpa.gov/-/media/Aep/energy-efficiency/emerging-technologies/ET-Documents/Low-GWP-Refrigerant-Report-FINAL-DRAFT-rev-6-2-2017.pdf

Carbajal, P., & Kanter, D. (2009, December 27). PDF. Amsterdam; Greenpeace International. https://www.greenpeace.org/usa/research/hfcs-a-growing-threat/

Elkins, J. W. (1999). Chlorofluorocarbons (CFCs). The Chapman & Hall Encyclopedia of Environmental Science, 78–80. https://gml.noaa.gov/hats/publictn/elkins/cfcs.html

Navarro, R., Eibisch, S., & Schneider, J. (2019, July 14). Implications of natural refrigerants for Cooling Technologies. energypedia. https://energypedia.info/wiki/Implications_of_natural_refrigerants_for_cooling_technologies


Emily Robins is a third year Creative Industries student at Ryerson University. She specializes in fashion and interior design.

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