One of the basic components selected when installing a walk-in cooler/freezer or any field-assembled refrigeration system is the metering device, typically the thermostatic expansion valve (TXV).
The TXV needs to be selected to match the Btu capacity of the system’s evaporator and compressor. Normally, these valves are rated in tons of refrigeration, so you need to remember that 1 ton of refrigeration equals 12,000 Btuh.