the subcooling and superheat

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the chiller composed by a screw compressor, a water-cooled shell-and-tube condenser, a thermal expansion valve and a dry-expansion shell-and-tube evaporator, from the ARI 550/590-98, the standard inlet and outlet cooling temperature are 85F and 95F, the chilled water ranged from 54F to 44F. then I have some questions as follow:
(1) what should be appropriate sub-cooling for this style of unit?
(2) what should be appropriate approach for the DX shell-and-tube evaporator?
(3) what should be the super-heat values for the evaporator and the system(super-heat of suction line)
in addition, the approach for flooded evaporator is
Approach_flooded=Tout_chilled_water-Tsat, but DX shell-and-tube evaporator always equipped an external balance thermal expansion valve, so how to define the approach of DX evaporators. in my mind, Approach_DX=Tout_chilled_water-Tout_refrigerant, where Tout_refrigerant is the actual refrigerant outlet temperature of the DX evaporator, I don't know is it correct.