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Characteristics of R744 |
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Applications |
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| What is R744? |
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R744 is the chemical reference for carbon dioxide (CO2) used as refrigerant. It is a naturally occurring substance that can be applied as a working fluid in different heating and cooling applications, due to its excellent heat transfer properties and its high volumetric cooling capacity. |
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| Are R744 and CO2 the same thing? |
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Yes. According to industry standards, each refrigerant receives a nomenclature starting with the letter R (for Refrigerant) and a number, which follows an order depending on the "family" the substance belongs to. R744 / R-744 is hence the standard nomenclature for CO2 used as a refrigerant: "7" indicates the natural fluid while "44" refers to the fluid's weight. The term R744 is applied when referred to the refrigerant itself, and CO2, and/ or CO2 Technology is used when referring to an application or use. |
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| What are the main characteristics of R744? |
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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. |
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| Why is R744 environmentally friendly? |
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Applying R744 in vapour compression applications reduces significantly the amount of greenhouse gas (GHG) emissions released to the atmosphere, which are at the origin of climate change. Besides, R744 systems are more efficient than current systems in most climate conditions, and therefore indirect emissions of GHG resulting from energy consumption are also reduced.
As an example: Given that, on average, Mobile Air Conditioning (MAC) is activated in 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 emissions reductions by using R744 is also significant.
For more details see the section Environment under Mobile Air Conditioning. |
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| Does R744 have any impact on the Ozone layer? |
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No, R744 does not contribute in any sense to the depletion of the ozone layer. |
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| Is R744 flammable? |
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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. |
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| Is R744 toxic? |
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R744 is not toxic at moderate concentrations. Given the small system charge used for heating and cooling applications, R744 thus presents minimal health risks. In the US, for example, this is reflected by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) with the common standard ASHRAE 34, which lists R744 as Safety Class A1 - a low toxic, non-flammable refrigerant.
When inhaled at high concentrations, however, carbon dioxide can lead to a risk of asphyxiation, since it displaces oxygen. In such case it would produce a sour taste in the mouth and a stinging sensation in the nose and throat combined with dizziness. |
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| Where does the CO2 used in refrigeration come from? |
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The refrigerant used in MAC or 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 refrigerant. |
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| Is R744 a totally new refrigerant? |
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Not exactly. CO2 was already used as a refrigerant in the mid-nineteenth century and its use steadily increased, reaching a peak in the 1920s. After that, the natural refrigerant was displaced by chlorofluorocarbons (CFCs) that operated at much lower pressures. Due to the impact on the environment of CFCs, and later HFCs, CO2 was re-evaluated as an alternative refrigerant in the late 1980s. A new way to contain the high pressure was discovered by Professor Gustav Lorentzen and his group of researchers from Norway, giving way to the application of transcritical R744 to different heating and cooling systems. |
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| What are the main benefits of R744 in Hot Water Heat Pumps? |
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Today, directly-fired hot water heaters are common, mostly fired either with gas or oil. A R744-based heat pump is more environmentally friendly, features high energy efficiency and provides safer operation. In addition, it is more cost-efficient as it provides storage for hot water needed during the day that can be heated at night when electricity is available at a lower price (night tariff).
Compared to the water heat pumps operated with HFCs, R744 heat pumps will provide higher water temperatures and thereby eliminate risks of bacteria. R744 will also has the clear advantage of a lower global warming impact. |
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| What is the state of development in this field? |
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The first "EcoCute" units were commercialised in Japan in 2001. Estimations show that by the year 2010, over 5 million units would be in operation in the Japanese market. Other markets (i.e. Europe, rest of Asia) are foreseen to follow soon. |
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| What are the main benefits of R744 in commercial refrigeration? |
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R744-based commercial refrigeration and freezing feature:
Reduced emissions of greenhouse gases
Space savings for piping arrangements (self-contained system)
Reduced costs of piping arrangements and insulation
Energy efficiency |
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| What is the state of development in this field? |
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There are several ongoing projects with R744 at advanced degree of completion. Some refrigeration cabinets working with R744 are already part of supermarkets in Europe (i.e. UK, Switzerland, Belgium), and large-scale production of components could follow soon if the market conditions evolve favourably. |
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