How to calculate AFN combined natural and mechanical ventilation in Energy Plus

energyplus
severe-error
airflow-network
zone-exhaust
natural-ventilation
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Hi, I want to check the airflow when exhausting air at a constant airflow rate from a particular room and taking in raw outdoor air through a window in another room.(the room is negative pressure ventilation) I made IDF and run simulate but failed with following error messages.

* Severe * The number of entered AirflowNetwork:Distribution:Component:Fan objects is 1