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Since you are modeling a central VAV system, I assume that you are using a SetpointManager:MixedAir object to account for mixing of outdoor air and heat added to the supply air from the central fan. We have found that if you want to use EMS to override setpoints, it's best to do the following:

1. assign a SetpointManager:Scheduled object to control the last supply node after the VAV system and reference a schedule of a constant temperature value (say 55F)
2. assign a SetpointManager:MixedAir object to account for OA mixing and central fan heat addition upstream from the last supply node
3. use an EMS actuator to override the value of the schedule referenced by the SPM:Scheduled object

The combination of SPM:Scheduled and EMS will essentially replace the SPM:Warmest and SPM:OutdoorAirReset objects. The reasoning for overriding the schedule value is because during each timestep, EnergyPlus determines schedule values before setpoint and availability control.

If Chandan's approach doesn't work, the EMS components will be much more involved to reset SAT and update supply flow properly. One possible strategy for defining the "worst case" scenario in a zone is the case when the zone air temperature exceeds cooling thermostat setpoint by 1F. For that case, you could force the VAV SAT to the low value of 55F. To do this, you will need to:

1. Create sensors to measure zone air temperature, cooling setpoint temperature, and predicted sensible cooling load
2. Create sensor to measure OA DB
3. Create actuators to override SAT schedule value and supply fan flow rate
4. Create program and subroutine to:
   • compare OA DB to the high (65F) and low (55) values
   • compare zone air temperature to cooling setpoint temperature to determine "worst case" scenario that triggers reset
   • override SAT schedule actuator according to combination of those two comparisons
   • override fan flow rate actuator according to SAT and predicted sensible cooling load

To override setpoint operation, be sure to choose a Program Calling Point before "AfterPredictorAfterHVACManagers" in order for the actuator to override behavior in the current timestep instead of the following timestep. Also, be mindful that EMS sensors use output variable values from the previous timestep.