I am looking at an Energy Plus model with a VAV system with AirTerminal:SingleDuct:VAV:Reheat terminal units. I am seeing that the reheat coil is operating sometimes when the output variable Zone Predicted Sensible Load to Setpoint Heat Transfer Ratehas the value zero. I looked at the zone temperature and at these times the reheat coil does need to operate to maintain the heating setpoint. Why is the predicted load zero, while zone heating from the reheat coil is needed to maintain the zone heating setpoint? And, how does the reheat coil determine what wattage to output in this case?

This is happening in my test file where I have been messing with the system controls, but I also looked at one of the example files for a VAV reheat system, and I see the same thing happening there always at the end of the day. Here are some graphs of the results over a couple of (winter) days:

First, the Heating Coil Heating Rate for the terminal unit heating coil and the Zone Predicted Sensible Load to Setpoint Heat Transfer Rate. You can see the heating coil is sometimes operating when the predicted sensible load to setpoint is zero.

Next, a graph of the zone temperature, heating and cooling setpoints for the same time window. You can see that the heating coil is just maintaining the heating setpoint when it operates at zero predicted zone load.

Thanks in advance for any ideas.

Some context: the actual designed system I am trying to model is a single zone variable volume, variable temperature system with no terminal reheat. I would like to control my system so that all heating and cooling occurs at the AHU heating and cooling coils, and eventually I want to remove the terminal reheat assuming I can get the model to work without it.