Different about Return Air Temperature of Same Zone

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Hi everyone,

I had modeled a simple zone with ElectricEquipment:ITE:AirCooled, and HVAC like below.

Firstly, I set the fraction of OutdoorAir:Mixer at 0% which means not allow outdoor air, and set the DX Cooling Coil temperature setpoint 24 C. I checked that the temperature that I supplied for the zone was 24 C and the return air temperature was 35 C.

Secondly, I used EMS to control the fraction of OutdoorAir:Mixer, and the DX Cooling Coil temperature setpoint was still 24 C. I checked that the temperature that I supplied for the zone was 24 C but the return air temperature was 45 C.

I wonder why I had this different temperature of return air? I used the same model and ElectricEquipment:ITE:AirCooled, I just used outdoor air and supply the same temperature for my zone. And why the DX Cooling Coil Electricity is the same when I used one case had only the outdoor air and one case had mixed air (return air and outdoor air), I think different input temperature for Cooling Coil cause different electrical consumption?

Here my HVAC System consists of OutdoorAir:Mixer, Coil:Cooling:DX:SingleSpeed, Fan:VariableVolume and AirTerminal:SingleDuct:ConstantVolume:NoReheat:

Thank all your supports.