retrofit on a Reefer-vessel

Hi there!
I would like to hear, if any of you have any experience with retrofit of large-scale systems. I'm currently doing a study for my Bachelor degree in Marine Engineering and would like some input.

The system is using R22 and the project is to choose an alternative refrigerant for the ship. It is a large system, which contains approx. 5000 kg. of R22 and have 5 screw compressors (2 SAB 163 HF & 3 SAB 128 HF) and 46 evaporators of the DX-type.
The system needs to be able to work from -29 degr. C when transporting frozen goods to + 13 degr. C when transporting bananas, so I'm currently thinking about using R407C as a replacement refrigerant but this leads to a huge retrofit procedure where all seals need to be changed because an oil change to POE oil is necessary. But it seems that almost any replacement refrigerant have the same problem.
Regarding the low temperature there might be a problem, due to the content of R134a in many HFC refrigerants. Another problem is that the system is only approved to have a working pressure of maximum 22 bar. at a temperature of 50 degr. C.

So, as you can see, there are many factors which needs to be dealt with :confused:

Hope that I can get some information from you guys:)
Best regards, Karsten