Floor heat control

I service a building where all of the apartments have the floor heating wired in this manner (see image). The thermostats are permanently on for all 3 rooms with the load of each going through the NC contactor and then through a cbus relay channel. The coil of the contactor is controlled by a further cbus relay channel.
I'm struggling to understand why this arrangement is necessary and was hoping that someone might have an answer?
The individual load for each heating is less than ten amps and i cant find anything that triggers ch4 to open the contactor. I thought that it might be to provide an "all off" control-its not but if it was its unnecessary.

 

The contactor not necessary unless the contactor is use for load shedding when AC is on Cooling ?? that could have be done in CBus if there is a touchscreen or something with logic.

 

Yes there is a TS.
So is this basically if the AC is on the contactor will open which obviously makes sense❓
There is also an an AUX input unit on the project- I’m going to guess that’s where cbus is getting a signal from AC that it’s on.