Fan Control

Fan control in the VAV application is carried out based on the type of fan installed in the system and occupancy status:

• series fan: works only as ventilator regardless of the heating/cooling demand, in occupied or standby statuses (standby only if the StandbySeriesFan variable is activated),

• parallel fan: works on heating demand in the HVAC mode set to Auto or Heat, regardless of the occupancy status.

Each type of fan can controlled in digital and analog mode set in the FanControlMode variable:

• digital (TO4): on/off,

• analog (AO3): min./max. speed (binary mode available in occupied, bypass and, optionally, standby statuses) or linearly according to the heating/cooling demand and within limit speeds set in the MinFanSpeed (by default, 20%) and MaxFanSpeed (by default, 100%) components.

Depending on the HVAC Mode settings (AirflowSetpointCalculator component):

• Auto:

  • parallel fan: working on heating demand,

  • series fan: working if occupied/bypass or standby (if allowed);

• Heat:

  • parallel fan: working on heating demand,

  • series fan: working only on heating demand if occupied/bypass or standby (if allowed);

• Cool:

  • parallel fan: inactive,

  • series fan: working only on cooling demand if occupied/bypass or standby (if allowed);

• MorningWarmUp:

  • parallel fan: if the WarmUpParallelFan variable is set to true, the parallel fan is active in this mode,

  • series fan: ventilator set to the maximum speed;

• PreCool:

  • parallel fan: inactive,

  • series fan: ventilator set to the maximum speed;

• NightPurge:

  • parallel fan: inactive,

  • series fan: ventilator set to the maximum speed;

• Off: both types of fan disabled;

• Fire:

  • parallel fan: inactive,

  • series fan: set to the maximum speed.

For safety reasons, the fan is started with a delay set in the FanDelayOff variable (by default, 30 s), which purpose is to cool down the reheater (for systems with a water reheater, the delay may be cancelled and set to 0 s).

The fan can work in four modes defined in the FanCommand variable:

• Auto: fan works according to the demand and type of the fan,

• MaxSpeed: fan works with the maximum speed set in the Max Fan Speed slot,

• MinSpeed: fan works with the minimum speed set in the Mix Fan Speed slot,

• Stop: fan stops working.