HVAC Operation controlling Water Mass Flow Rate

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Hello All,

I am trying to develop a control system where the idea is to create a PID for Water Mass Flow Rate using BCVTB for the Heated Floor HVAC system. I used the Heated Floor Template from Designbuilder and created 4 rooms where 2 of them are controlled via the HVAC (Bathroom and Kitchen).

Now using the external interface, I have only supplying 0.01 kg/s mass flow rate to the HVAC system in Kitchen. Based on the system in the Designbuilder I have exported the IDF and collected the data from the IDF. Attached is a snippet of data collected from the IDF as CSV.

Question is:

• Why the mass flow is not always constant in the simulation? What defines the water mass flow logic in the heated floor in HVAC?
• I have set the Thermostat setpoint as 22 and Setback as 18. But the Zone Thermostat Heating Setpoint Temperature keeps on varying, mostly going above the setpoints. Why so much variation?
• I see that even where there is no occupancy, the HVAC system is ON (from the flow value). Why is that?

Here is the link to the documents (https://drive.google.com/drive/folder...)

P.S - IDF file is edited manually later after exporting from Designbuilder.