I would like to add a return fan to an AHU but not quite sure where I should put it in. I put an additional fan in the Supply Equipment side of the air loop, just before the AirLoopHVAC:OutdoorAirSystem. But when I check the idf file, the fan is still in the supply branch and in this branch, there are two fans. Is it correct? What about relief fan?
A return fan should be placed on the node before the AirLoopHVAC:OutdoorAirSystem, as you described. This fan will show up as the first component listed in the branch that describes the air loop's "Primary Air System", which is the 'supply side' of the air loop:
A relief fan will be placed on the relief air node of the outdoor air system. In the IDF, the fan will be listed as a component in the AirLoopHVAC:OutdoorAirSystem:EquipmentList object, not on the air loop's supply branch:
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