Walk in cooler, freezer or cold room (Detailed HVAC)

On the Activity tab, set the cooling setpoint and setback temperatures to the required freezer zone air temperature.
Add a PTHP zone unit to the HVAC zone group. These units can cool down spaces below 0ºC.
Then set the unit's (Fan + DX Coil) characteristics in a way that it won't consume any energy.

Fan unit:

PTHP's DX Cooling coil:

Note that "All 0" curves have all their coefficients set to 0. This means that the curve output is always 0.

The final results show that freezer temperature is quite well maintained (there are some peaks, probably caused by sizing) and the PTAC does not consume any energy:

Following these steps allows you to cool zones down to very low temperatures.