Outdoor Air Mixer[LINK]
The OutdoorAir:Mixer is the fundamental component of the outside air system. There should always be one OutdoorAir:Mixer in an AirLoopHVAC:OutdoorAirSystem. The outside air mixer splits the primary air system (AirLoopHVAC) return air into relief and recirculated air streams. Then it mixes the outside air stream with the recirculated air stream to obtain the mixed air stream. The outdoor air mixer has 2 inlet flow nodes: the return air node and the outside air node. It has 2 outlet flow nodes: the relief air node and the mixed air node.
Given the air mass flow rates and conditions (humidity ratio, specific enthalpy) at the return air node, relief air node, and outside air node, the simulation uses mass and energy balance to calculate the air mass flow rate, humidity ratio, and specific enthalpy at the mixed air node. The mixed air temperature is calculated from the mixed air humidity ratio and specific enthalpy using the EnergyPlus psychrometric routine PsyTdbFnHW.