Frequently Asked Questions about R744

Please go over the categories below to find the answers to your questions.

Question What is R744?
R744 is the HVAC&R industry reference for carbon dioxide (CO2) used as a refrigerant. It is a naturally occurring substance that can be applied as a working fluid in different refrigeration, cooling and heating applications due to its excellent heat transfer properties and its high volumetric cooling capacity.
Question Are R744 and CO2 the same thing?

Yes. According to industry nomenclature, each refrigerant starts with the letter R (for refrigerant) and a number, based on the "family" to which the substance belongs. R744 / R-744 is the industry name for CO<sub>2</sub> used as a refrigerant: "7" indicates that it’s a natural fluid while "44" refers to the fluid's molecular weight (g/mol). The term R744 is applied when referring to the refrigerant itself, and CO<sub>2</sub> and/or CO<sub>2</sub> technology is used when referring to an application or use.

Question What are the main characteristics of R744? 

R744 is:

  • Non-toxic
  • Non-flammable
  • Non-ozone-depleting
  • Environmentally friendly, with a Global Warming Potential = 1

A more detailed explanation of each of these features follows below.

Question Why is R744 environmentally friendly?

Applying R744 in vapor-compression applications reduces significantly the amount of greenhouse gas (GHG) emissions released into the atmosphere, which is the cause of climate change. In addition, R744 systems have the potential to be more efficient than traditional systems in all climate conditions, and therefore indirect emissions of GHG resulting from energy consumption are also reduced. 

For example, given that, on average, mobile air conditioning (MAC) is activated about 60% of the time a car is in use over its lifetime, the choice of the low global warming refrigerant R744 is a key element for improving the environmental performance of a car. For other applications, such as heat pump water heating or commercial refrigeration, the potential for emission reduction with R744 is also significant.

Question Does R744 have any impact on the ozone layer?
No, R744 does not contribute in any way to the depletion of the ozone layer.
Question Is R744 flammable?
No, R744 is not flammable and presents no risks in case of interaction with other substances or chemical blends. CO2 is applied in many fire extinguishers.
Question Is R744 toxic?

R744 is not toxic at moderate concentrations. Given the small system charge used for cooling and heating applications, R744 thus presents minimal health risks. In the U.S., for example, this is reflected by the classification of R744 by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) in its ASHRAE 34 standard, which lists R744 in Safety Class A1 - a low toxic, nonflammable refrigerant. 
When inhaled at high concentrations, however, carbon dioxide presents a risk of asphyxiation, since it displaces oxygen. In such a case it would produce a sour taste in the mouth and a stinging sensation in the nose and throat combined with dizziness.

Question Where does the CO₂ used in refrigeration come from?
The CO2 refrigerant used in refrigeration and heat pumps is an industrial waste product. Some industrial companies have developed systems to extract CO2 from their plants to process it and sell it as a refrigerant.
Question For which applications is R744 suitable?

R744 can be used in many refrigeration and cooling applications such as supermarket and industrial refrigeration, ice rinks, data centers, and mobile air conditioning (MAC) in vehicles and buses, as well as heat pump applications like space and hot-water heating. CO<sub>2</sub> technology is extremely efficient in heating water, explaining the success of the Japanese "EcoCute" heat pump water heater, which can also be combined efficiently with space heating.

Question What are the main benefits of R744 in commercial and industrial refrigeration?

R744-based commercial and industrial refrigeration and freezing features:

  • Reduced emissions of greenhouse gases
  • Space saving in piping arrangements (self-contained system)
  • Reduced costs of piping arrangements and insulation
  • Energy efficiency
Question What is the state of development in this field?

Research into improving the operation and efficiency of R744 systems continues around the world.

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