How to implement centralized ventilation system without heating or cooling in energyplus idf editor?

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Since HVACTemplate:Zone:Unitary has some fields named "Baseboard Heating...", I think that it can do the same as HVACTemplate:Zone:BaseboardHeat and more, and I guess that you can safely delete the HVACTemplate:Zone:BaseboardHeat objects after having reported their configurations to your HVACTemplate:Zone:Unitary objects... can someone with experience please confirm?

There is no reasons to get a Severe Error if the same name is applied to different Object Type. The error must be elsewhere.

You should go through the IDF, objects name, but I do not find any attached file

This is going to be the long way to get there, but it seems like it would benefit you..

If it were me, I'd download and install CBECC-Com which is a free software interface for doing code compliance in California. However, it runs on the EnergyPlus engine and installs with sample files, including two with DOAS systems (dedicated outdoor air system ==> aka centralized ventilation systems). Open one of the sample models such as Documents\CBECC-Com 2019.1.3 SP1 Projects\OtherTests2019\RetlSml-DOAS+FPFC19.cibd19, run it, and then find the IDF file for the proposed file in the project directory.. This will give you an idea of how a system would actually be set up, and you can modify from there.