Carbon dioxide and CO2 are very often the focus of discussions about the hole in the ozone layer as well as for other reasons. But maybe not everyone knows that CO2 is also an excellent gas that can substitute traditional gases employed as refrigerants, such as the classic freon which is correctly considered as a cause of the hole in the ozone layer.

Recently, the sector of refrigeration has been intensely involved in the research of alternative gases in order to limit the greenhouse effect. An example is ammonia, that however has important negative side effects in terms of toxicity and flammability. The most recent born is then the CO2.

There are in fact more and more cooling, refrigeration and conditioning plants on the market that are using CO2 in their thermal cycle, carbon dioxide. CO2 is a natural gas, with therefore a huge green aspect. But there are clearly also some complexities and implications, related to the fact that CO2 has state transitions are very high pressure levels, meaning 100, 120, 130 and up to 140 bars. And traditionally conceived refrigeration plants using freon work in the condensation phase at maximum pressure levels of 40-45 bars.

It means that the overall components and equipments usually employed in refrigeration plants must undergo an important technological upgrade in order to cope with CO2 working conditions applications. There are in fact already functioning plants using CO2 on the market, and therefore the suitable equipments already exist too, although maybe not covering the full range of power capacities. There is for example a quite wide range of compressors available for CO2 applications, even if not in all the sizes and power capacities.

Difficulties are instead related to connections, fittings and pipings, that must be able to cope with these high pressure working levels. But as well, working with high pressure levels also involves having high specific volumes, allowing for a reduction of the diameters of pipings.

Finally, another main aspect is related to thermal transfer, that requires to study special heat exchangers, in function of condensers and evaporators, able to work with the high pressure levels involved in CO2 applications. These exchangers can be brazed plate exchangers, employed as evaporators or condensers, or a thermal transfer array when using air heat exchangers. Anyway, these are ad hoc engineered equipments in order to work with CO2 at high pressure. A full range of CO2 heat exchangers is already available on the market, offering quite interesting power capacities, but clearly actually we’re still in a strong phase of study and engineering development.

 

Stay updated on the latest applications of thermal energy management by subscribing our monthly Tempco Newsletter – Solid Temperature.