The system monitors calls for unoccupied heating or cooling when you select a representative zone at the VZC. When the representative zone temperature drops below the unoccupied heating setpoint, or rises above the unoccupied cooling setpoint, it triggers the unoccupied call for heating or cooling. The unoccupied heating or cooling mode ends when the call is satisfied for a 30-second time period.
RTU
The RTU turns on all heating stages after a call for unoccupied heating. If the system controls a heating valve instead of heating stages, the heating valve opens to 100%. During the unoccupied heating operation, the supply fan adjusts the duct static pressure to meet the current setpoint for the duct static pressure. The economizer is closed.
While in unoccupied mode, the economizer is closed by default. However, during a call for cooling, the economizer provides cooling if free cooling is available. If free cooling is not available, the system requests cooling from the RTU. This adjusts the SAT to its setpoint.
The supply fan remains off when the system is unoccupied. Cooling and heating also remain off when no call for unoccupied cooling or heating is issued. The economizer closes.
VAV box
When the zone temperature of the representative zone drops below its unoccupied heating setpoint, the zone controller requests unoccupied heating and adjusts it to the Cooling Max Flow setpoint. Zones that do not require unoccupied heating move to their Unoccupied Cooling Min Flow. For example, zones with temperatures above the unoccupied heating setpoints and local supplemental or box heat stage, adjust the zone temperature to meet the unoccupied heating setpoint. Supplemental heat is used before box heat if both heating strategies are present.
The zone controller requests unoccupied cooling and adjusts to its cooling maximum flow when the zone temperature of the representative zone rises above its unoccupied cooling setpoint. Zones that do not require unoccupied cooling move to the unoccupied cooling minimum flow. For example, zones with temperatures below the unoccupied cooling setpoint. Non-representative zones that call for cooling or heating, do not start the RTU. When heat is needed, the local fan operates when the local heat command rises above 5%.