As the name implies, it's the return air node.

An AirLoopHVAC:OutdoorAirSystem has four nodes:

• Return Air Node
• Relief Air Node
• (Outside) Inlet Air Node (it gets air from a virtual "OutdoorAir:Node" that represents environmental conditions)Node
• Mixed Air Node

All the air in the return path of the AirLoopHVAC gets to the Return Air Node, at which points a fraction can go to the Relief Air Node (to the outside) and the rest goes to the mixed air node. The mixed air node gets air from the return air node and the outside inlet node.

Source:

• https://github.com/jmarrec/EnergyPlus/blob/develop/src/EnergyPlus/MixedAir.hh#L218
• https://github.com/jmarrec/EnergyPlus/blob/develop/src/EnergyPlus/MixedAir.cc#L3237

As the name implies, it's the return air node.node...

An AirLoopHVAC:OutdoorAirSystem has four nodes:

• nodes: * Return Air Node
• Node * Relief Air Node
• Node * (Outside) Inlet Air Node
• Node * Mixed Air Node

All the air in the return path of the AirLoopHVAC gets to the Return Air Node, at which points a fraction can go to the Relief Air Node (to the outside) and the rest goes to the mixed air node. The mixed air node gets air from the return air node and the outside inlet node.

Source:

• https://github.com/jmarrec/EnergyPlus/blob/develop/src/EnergyPlus/MixedAir.hh#L218
• https://github.com/jmarrec/EnergyPlus/blob/develop/src/EnergyPlus/MixedAir.cc#L3237