Why the mass flow rate on a system node is zero

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Hello everyone, i am currently testing and modifiying the Energyplus example file. The model i am using is 'DesiccantCVRh.idf' in the example folder. The original model works well and i made some modification on the secondary air flow of the HeatExchanger. The original model uses the relief air as the inlet of the Secondary air flow, but i want to use the outside air as the inlet air to cool down the primary air flow. To do so, i disconnect the relief air and inlet side of the secondary air flow of heat exchanger. Instead, i created an Outside Air Inlet Node4 and Fan and link these two new objects to the inlet side of the secondary air flow of Heat exchanger. After running the simulation, i found the the air temperature of primary air flow at the inlet and outlet of Heat exchanger is equal and the air mass flow rate at the Outside Air Node4 (inlet node of the secondary air flow) was zero. The modified system is shown below where the main air loop branch include the Outdoor air system, supply fan and cooling coil. I checked the error report and found the relevant warning information about the outside air node4, just showing below: It says the connection of the outside air node is not correct. In my model, i just creasted a outdoor node list and put this outside air node on the list and i have nothing operation of this node on other place. So can anyone give me some idea on this issue, many thanks!