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The use of setback/setup in the thermostat temperature schedules causes zone sizing to overestimate the load during the setup time step. For example, as the heating set point temperature changes from 16C to 22C, the load prediction becomes very large. The prediction calculates the capacity needed to bring the zone temperature all the way up to the new temperature set point.

If you are autosizing, you can either use constant temperature set points during sizing on design days, or use an averaging approach to smooth the sizing results using the Timesteps in Averaging Window input in the Sizing:Parameters object:

Timestep,4;

Sizing:Parameters,
  1.3,                     !- Heating Sizing Factor
  1.3,                     !- Cooling Sizing Factor
  8;                        !- Timesteps in Averaging Window

If you are not autosizing, this result may be due to unlimited capacity. For example, in the ZoneHVAC:IdealLoadsAirSystem.

From your graphs, I cannot tell what happens after the setup time step. There may be a spike in capacity (power) during the setup time step, but shortly after that time, certainly near the setback time step, the capacity (power) for each simulation should be very near. Try isolating a single day and view the same graphic over a shorter period of time.

The use of setback/setup in the thermostat temperature schedules causes zone sizing to overestimate the load during the setup time step. For example, as the heating set point temperature changes from 16C to 22C, the load prediction becomes very large. The prediction calculates the capacity needed to bring the zone temperature all the way up to the new temperature set point.

If you are autosizing, you can either use constant temperature set points during sizing on design days, or use an averaging approach to smooth the sizing results using the Timesteps in Averaging Window input in the Sizing:Parameters object:

Timestep,4;

Sizing:Parameters,
  1.3,                     !- Heating Sizing Factor
  1.3,                     !- Cooling Sizing Factor
  8;                        !- Timesteps in Averaging Window

If you are not autosizing, this result may be due to unlimited capacity. For example, in the ZoneHVAC:IdealLoadsAirSystem.

From your graphs, I cannot tell what happens after the setup time step. There may be a spike in capacity (power) during the setup time step, but shortly after that time, certainly near the setback time step, the capacity (power) for each simulation should be very near. Try isolating a single day and view the same graphic over a shorter period of time.

ZoneHVAC:IdealLoadsAirSystem,
  A5 , \field Heating Limit
     \type choice
     \key NoLimit
     \key LimitFlowRate
     \key LimitCapacity
     \key LimitFlowRateAndCapacity
     \default NoLimit
  N6 , \field Maximum Sensible Heating Capacity