R744 or CO2 info
Refrigerant R744 is good but not without its problems
Refrigerant R744, i.e. carbon dioxide (CO2), is an environmentally friendly refrigerant. Its ODP is zero and its GWP is as low as 1, which means that it has even less global warming potential than hydrocarbons.
Use and applications
Carbon dioxide has many applications: in gas form, for example, it is used in the food industry for cooling, storage and pH management purposes. Carbon dioxide prevents microbial growth, which means that it is used as a packaging gas for many food products.
Carbon dioxide is often used as a secondary refrigerant alongside ammonia.
As a refrigerant, it does not function exactly the same as hydrocarbons and the operating pressures may also be elevated as a result. For this reason, the efforts to develop improved equipment are ongoing to enable wider use of carbon dioxide. An asset of carbon dioxide plants is that the pipe size is significantly smaller than with other refrigerants.
Various plants that utilise carbon dioxide have been in test operation for many years. C02 is suited to refrigeration plants with either direct evaporation or pump circulation. It is an excellent refrigerant for freezing plants, in which it can provide evaporation temperatures of up to -50°C.
Many carbon dioxide plants are already in use in Europe, and these experiences will be helpful in the development and construction of new plants.
R744 replacement refrigerants
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Want to know more?
Read more in Mikko Muuronen’s engineering thesis on the use of carbon dioxide as a refrigerant (2016).
Carbon dioxide was used as a refrigerant from the mid to late 19th century. When the use of hydrofluorocarbons began in the 1930s, carbon dioxide began to fade out of the picture. Due to the low environmental impact, the use of carbon dioxide as a refrigerant is once again under active development.
An interesting detail is that carbon dioxide has been used alongside halons in the fire extinguishing and smoke detection systems of ship engine rooms, for example. Since its operation within a system is rather slow, minimum release times have been specified for carbon dioxide. Read more about the matter in the Marine Engineering Study materials, for example.