Note: This method requires additional scheduling objects to be created in your HVAC system.
Figure 5 - Commanding Schedule Object Directly
In this scenario, according to the BACnet specification, if you set the schedule object's OUT OF SERVICE flag to TRUE, then the present value property of the schedule object will no longer be calculated internal and can be commanded directly by an external source. To revert to the default schedule, set the schedule object's OUT OF SERVICE flag to FALSE.
Since most scheduling objects are created for fixed building schedules, these schedules will typically start/stop the entire system including the individual room VAV boxes. Choosing this method requires the creation of room-level scheduling objects since the ultimate goal is to perform dynamic room-level scheduling.
You could expand the user-friendliness of the switchover by adding a global switch binary object and have it set the OUT OF SERVICE flag directly to all of the schedule objects as an interlock so that the operator only has to switch one point to enable or disable the automatic scheduling.