Temperature behavior at the Dual Setpoint Thermostat model

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Hello!

I am exploring the 2 Zone Data Center model included in the EnergyPlus installation. You can see the model description here at NREL github-repository.:

The model has a thermostat with two setpoints. It is described as follows:

ZoneControl:Thermostat,
    West Zone Thermostat,    !- Name
    West Zone,               !- Zone or ZoneList Name
    Zone Control Type Sched, !- Control Type Schedule Name
    ThermostatSetpoint:DualSetpoint,  !- Control 1 Object Type
    Temperature Setpoints;   !- Control 1 Name
ZoneControl:Thermostat,
    East Zone Thermostat,    !- Name
    East Zone,               !- Zone or ZoneList Name
    Zone Control Type Sched, !- Control Type Schedule Name
    ThermostatSetpoint:DualSetpoint,  !- Control 1 Object Type
    Temperature Setpoints;   !- Control 1 Name
ThermostatSetpoint:DualSetpoint,
    Temperature Setpoints,   !- Name
    Heating Setpoints,       !- Heating Setpoint Temperature Schedule Name
    Cooling Setpoints;       !- Cooling Setpoint Temperature Schedule Name
Schedule:Compact,
    Zone Control Type Sched, !- Name
    Control Type,            !- Schedule Type Limits Name
    Through: 12/31,          !- Field 1
    For: AllDays,            !- Field 2
    Until: 24:00,4;          !- Field 3
Schedule:Compact,
    Heating Setpoints,       !- Name
    Temperature,             !- Schedule Type Limits Name
    Through: 12/31,          !- Field 1
    For: AllDays,            !- Field 2
    Until:  7:00,20.0,       !- Field 3
    Until: 17:00,20.0,       !- Field 5
    Until: 24:00,20.0;       !- Field 7
Schedule:Compact,
    Cooling Setpoints,       !- Name
    Temperature,             !- Schedule Type Limits Name
    Through: 12/31,          !- Field 1
    For: AllDays,            !- Field 2
    Until:  7:00,23.0,       !- Field 3
    Until: 17:00,23.0,       !- Field 5
    Until: 24:00,23.0;       !- Field 7

My suggestion was HVAC equipment should try to return the zone temperature to the given range, and should be below 23 degrees, but it always remains above these values.

If I change, e.g., the heating setpoint value, the difference will only be that the temperature curve decreases or rises accordingly setpoint direction change (up or down), but everything will also be above the upper limit (heating setpoint).

On the plot, you will see the same zone temperatures. This is because I changed the air flow calculation method in the second (EastZone) to AirFlowFromSystem which the same as WestZone:

  ElectricEquipment:ITE:AirCooled,
    EastDataCenter_Equip,    !- Name
    East Zone,               !- Zone Name
    FlowFromSystem,          !- Air Flow Calculation Method
    !#FIX! FlowControlWithApproachTemperatures,  !- Air Flow Calculation Method

I read the documentation saying (Input Output Reference, pp. 1.35.1.2.5 Zone Thermostat Heating Setpoint Temperature), but I couldn’t understand how to explain this behavior. Can someone help me?