This early refrigerant has again attracted great interest. High latent heat and heat transfer factor, in combination with high-pressure and density of operating conditions, provides the ability to produce large amounts of cooling with very low volume compressors and small-diameter pipelines. Its main drawback is its low critical temperature. The effectiveness of the vapour compression cycle is very bad if condensing temperature approaches the critical temperature. This is also a lack of HFC refrigerants, but carbon dioxide is much worse.
It is used in low stage of the cascade systems using the vapour compression cycle. In the transcritical cycle is very effective, where the heating requirement calls for water heating in a wide range of temperatures, as in the case where the hot water for services is formed from the cold water supply. In these cases, gas counter-flow cooler is a good solution. Much work has also been done on the use of carbon dioxide for vehicles Кондиционер.
Another aspect of transcritical R744 cycle is the ability to revert to conventional vapour compression cycle in conditions of low ambient temperature.
A good average seasonal efficiency can be achieved in those places where the heat can be rejected at a temperature below 30C throughout the year, where the work in supercritical mode only at high outside temperatures. High pressures and high pressure differences allow the use of smaller tube. Condensing temperature may be significantly reduced at low temperatures and is quite sufficient pressure differential drive refrigerant around the circuit. The use of the economizer can significantly improve the sub-critical cycle performance.
Refrigerants