Adding central Mechanical ventilation in Energyplus to an existing building with baseboard heaters

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Dear Colleagues and Professional, in my assignment I have an existing school building with already installed heating system using heatboards with hot water loops, my question is how can I add a centralized mechanical ventilation (No cooling) to the existing systems ? I have tried adding Airloop but I had the error of duplicating zone equipments ! Does anyone can recommend me a solution or has an example .idf file ?