The difference between the behaviour of different refrigerants
The two main refrigerants used in transport cooling behave differently with the change of temperature and pressure. This can be presented well with the known example of petrol and diesel engines. While petrol engines have a high torque, diesels work efficiently even at high speed. But these are still engines. Let’s meet the refrigerants!
The R134a refrigerant is used for „normal” cooling, meaning the load compartment does not have to be cooled under 0°C. (This refrigerant is also used in vehicle air conditioners.) If the temperature in the load compartment is lower the pressure of the refrigerant returning to the compressor can sink so low, that the refrigerant cannot function effectively.
If we need a lower temperature – like at the transport of frozen goods- the R404a, or it’s more nature friendly counterpart, the R452a, is the refrigerant we need. This substance has lower pressure needs, so even at lower returning refrigerant pressure the compressor can circulate the refrigerant effectively. The question comes naturally: what happens, when the load compartment temperatures high or the returning refrigerant temperature is low? Can refrigerant pressure get too high? The pressure rises in such cases, but cooling unit producers integrate pressure and flow control valves, that are able to optimize system pressures, even at critical conditions.
The most important factor in transport cooling is efficiency. We can say that you can achieve higher efficiency if you are using the right refrigerant. This also increases the life expectancy of your cooling unit. It is important to note, that the technical details of a unit, the pressure valves, feed valves are set for a given refrigerant. So the changing of the refrigerant to a different type or loading it with a different refrigerant is not suggested, and in most cases not economic. In our engine example this would mean, that you cannot fill the tank of a petrol engine with diesel fuel, because its cheaper.
