What is the PHE capacity?
The TXV size has to fit that capacity regardless the evaporting temp. When you get this info, you can determine the condensing unit size, Or you can check your 10 ton refrigeration unit capacity at -5C and then work out the TXV size and PHE capacity at your required water flow and leaving temp.

Remember that water freezez at 0C so you might need to add some glycol but that will decrease the unit capacity.