I am trying to simulate the ON and OFF cycles of the HVAC so that i can ascertain its heating and cooling time (time without the HVAC) over a 24 hour simulation. For this simulation i have considered a 10 degrees dead band temperature, 30 degrees setpoint temperature, 0 degrees outdoor dry bulb temperature, 45 degrees supply air temperature from the VAV terminal system. Also, only heating has been considered, hence i turned off the cooling coils in the model. My problem is that when i look at the output of the zonal air/mean temperatures(please see west zone), the results do no not seem to corroborate expected results based on practical experiments in a real building scenario.
For one, the HVAC heats up the zone(west zone ) very quickly and the temperature of the zone decreases sharply at OFF time (without the HVAC). For a building without cracks and openings( fully closed building), though it is expected that the building will heat up quickly but i am not very sure why the zone air/mean temperatures decrease sharply too. Please can anyone give me a logical reason why i have this type of result?
Second, observe at ON Time(HVAC), the zonal temperature quickly rises and stabilizes(Please see attached plot). Is there a form of PID Control going on? I am not sure why this happens. In reality, it is expected that the zonal temperature would gradually increase until it reaches the setpoint temperature. Is there a clear explanation for the sharp increase?(Please atached photo) Thanks as always. 
I have attached the IDF file and weather file herein: https://drive.google.com/file/d/1e1BsqdpdOndIfyR9bOQHv1mLXqk03smf/view?usp=share_link
Please any help would be greatly appreciated.
