FCU Modes

The FCU mode is a parameter defining how the FCU controller is operating. This parameter can have the following states:

OFF: in this mode, the FCU controller software is off, only the anti-frost procreation can start the FCU controller;
Auto: in this mode, the FCU controller switches between cooling or heating function based on the measurement temperature and effective setpoint temperature;
Heating Only: in this mode, the FCU controller can perform only heating function (dedicated for 2-pipe mode or if the cooling medium is not available: winter mode);
Cooling Only: in this mode, the FCU controller can perform only cooling function (dedicated for 2-pipe mode or if the heating medium is not available: summer mode);
Fan Only: in this mode, the FCU controller can perform only ventilation, heating and cooling functions are disabled.

For the remote mode control, the default application has the FCU_Mode network variable.

Name	BACnet ID	Modbus Address	Value	Function
FCU Mode	0	104	0	Off
			1	Auto
			2	Heating Only
			3	Cooling Only
			4	Fan Only

FCU mode network variable values description

OFF Mode

In this mode, the fan is switched off, all heating and cooling devices are disabled. This mode can be set from BMS (by writing 0 value to the FCU_Mode network variable). This mode is called if the Open Window signal is detected. In this mode, the anti-frost function is active.

Auto Mode

In this mode fan outputs, heating/cooling valves actuators and HTG/CLG relays are active and work with application algorithm. The cooling or heating algorithm is chosen based on current temperature and effective temperature setpoint with switching dead band defined in Switching_Cooling_Heating_Diff network variable. Switching between heating/cooling can be done only in Occupancy Mode. In Unoccupied or Standby mode FCU controller remembers and stays in previous function. If the controller comes back to the Occupancy mode, algorithm will calculate in which function it should work.

Switching between heating/cooling chart

Heating Only Mode

In the Heating Only mode, the application is running only with the heating algorithm. The fan outputs, heating valve actuator outputs, and HTG relay are enabled, while the cooling valve actuator outputs and CLG relay are disabled. This mode is dedicated for the 2-pipe system during winter mode or the 4-pipe system if the cooling medium is not available.

Cooling Only Mode

In the Cooling Only mode, the application runs only with the cooling algorithm. The fan outputs, cooling valve actuator outputs, and CLG relay are enabled, while the heating valve actuator outputs and HTG relay are disabled. This mode is dedicated for the 2-pipe system during summer mode or the 4-pipe if the heating medium is not available.

Fan Only Mode

In the Fan Only mode, only fan outputs are enabled, while heating and cooling valves actuators outputs and HTG/CLG relays are disabled. The fan is operated with the application algorithm.