CO2 vs Ammonia

CO2 scaling up

As for CO2, many companies see significant market opportunities for this natural refrigerant to be used more widely in industrial applications, thanks both to the generally lower cost of CO2 systems compared to their comparable ammonia counterparts, and their ability to provide significant amounts of heat reclaim.

Carbon dioxide (CO2 is one of the natural refrigerants which can be used as working Fluid in

various refrigeration applications along with the ammonia and hydrocarbons due to its eco-

friendliness, higher volumetric capacity, good heat transfer properties, etc. The present article

consists of two parts: A detailed comparative study of CO2-based transcritical refrigeration systems with conventional refrigerants-based systems in terms of both thermodynamic and heat transfer performances, and review of both theoretical and experimental researches on transcritical CO2 vapor compression cycle for various refrigeration applications including commercial product status.


The new hot topic is a return to carbon dioxide as a refrigerant. The previous two major problems of high pressure and high compressor temperature are found in fact to be advantageous. The very high cycle pressure results in a high fluid density throughout the cycle, allowing miniturization of the systems for the same heat pumping power requirements. Furthermore the high outlet temperature will allow instant defrosting of automobile windshields (we don't have to wait until the car engine warms up) and can be used for combined space heating and hot water heating in home usage.




Facilities using ammonia should have emergency response plans in place, with clear directions for how to stop or control the flow of ammonia.The plan should include thorough diagrams of all the parts of the refrigeration system including valves. You should also have a supply of breathing apparatus and protective clothing available for each team member in case of an emergency,

While ammonia is not considered a poison and has no reported long-term, adverse effects on human health, it can irritate the eyes, lungs and skin, according to OSHA.


Even in small concentrations, those in direct contact with the gas may experience irritated eyes or skin, coughing, congestion, difficulty breathing, and freeze-dried skin (similar to frost bite).

Workers who are exposed to the chemical should understand decontamination procedures relevant to ammonia, including flushing any affected areas with water and removing contaminated clothing.

Top 13 advantages of CO2 (R744)
















Environmentally benign

Low triple point

Low critical point

High pressure (which can increase system efficiency)

High refrigeration volumetric capacity

High heat transfer characteristics


Readily available

CO2 is a natural, safe and inexpensive refrigerant (12 times more economical than traditional HFC).

Its effect on the climate is 1,500 to 4,000 times less than that of synthetic refrigerants

The reduce the size of components and piping and enable the design of more compact systems

Top 9 disadvantages of Ammonia










The major disadvantage of ammonia as a refrigerant is its toxicity

Due to ammonia’s hygroscopic nature, it migrates to moist areas of the body, including the eyes, nose, throat and moist skin and may cause severe burn injuries

Skin and respiratory-related diseases are aggravated by exposure(6) and even possible fatality at higher concentrations

Liquid ammonia will cause frostbite since its temperature at atmospheric pressure is -28o F(7).

The Occupational Safety and Health Administration’s (OSHA) Permissible Exposure Level (PEL) is an 8-hour time weighted average of 50 parts per million (ppm).

The National Institute of Occupational Safety and Health has established Immediately Dangerous to Life Levels at 300 ppm for the purpose of respirator selection(1).

Concentrations of 5000 ppm can be lethal.

The American Industrial Hygiene Association (AIHA) has developed Emergency Response Planning Guidelines (ERPGs) for toxic substances to assist in planning for catastrophic releases to the community.

Ammonia vapors are a fire and explosion hazard at concentrations between 16% and 25%. Mixtures involving ammonia contaminated with lubricating oil from the system, however, may have a much broader explosive range.

 A review of carbon dioxide as a refrigerant in refrigeration technology

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