R-404A superheat

[michaelm]

B”H
I just gaining the experience of working with R-404A. It was a customer choice. I was told that with 404A I should keep min superheat of 6 - 10C. And even with 10C superheat still some drops can enter the compressor. I could not understand this. Suction tem-re is -12C it is a chiller. Would like to hear from you if is so? I appreciate very any help.
Regards.

[jpsmith1cm]

If the superheat is computed properly, then it won't be a problem.

[mad fridgie]

I personally have not had a problem with R404a, but I have heard of many who have. It is my understanding that the TXV sizing (including the orifice) is somewhat more critical that the older refrigerants, and the pressure drop across the valve is also more critical (constant liquid pressure required) They have been finding there is quite a bit of hunting happening (suction pressure up and down) As the valve opens (seemingly quite fast) the superheat reduces quickly, at this stage liquid droplets could carry over to the compressor. To reduce the chance of this carry over they increase the valve superheat setting.
This in itself will not stop the hunting, but stops carry over, you will find the suction pressure will drop slightly, as evap is not performing at 100% of design.

[michaelm]

Thank you so much both of you for the reply.