The situation in the question that you referenced does not apply to your building as you do not have two airloops feeding into your zone. The ventilation system in your case should be modeled modelled as an air loop and the radiator should be modeled modelled as a zone equipment.

The component Coil:Heating:Water Coil:Heating:Water is quite different from a radiator (as in real-life) and is not applicable to model radiators.

I suggest that you look at the example file named "VAVSingleDuctReheatBaseboard" about setting the system required to model your scenario (it is quite similar but not exactly). As you can see in the model, the component ZoneHVAC:Baseboard:Convective:Water can be used to model radiators. This in-turn is added to a plant loop (see BranchList). The Air Loop Main Branch (look under the Branch Class) in the example file would need to be adjusted based on the ventilation system of your building.