The function is used to prevent frost formation on the heat exchanger and/or reduces the load on the after heater while plate heat exchanger is in defrost mode with the by-pass open.

The preheater will activate in the selected running mode. The running modes are: constantly on, follow separate schedule, run while the unit is running or activate during defrosting cycle.

The preheater function requires a sensor to measure the temperature of the preheated air. The measurement is then compared to the setpoint and the difference is transformed to a PID regulated output signal.

Configuration example for the electric preheater to activate during defrosting cycle


Available options & Selection


Activate preheater function

Configuration > Functions > Function activation


| Yes | No |

Preheater configuration

Configuration > Functions > Preheater

Preheater function

| Preheating | Filter drying |


Type of preheater

| Water | Electric |

Preheater temperature sensor

... | Preheater temperature |

Start/Stop function

| Always running | Unit running |

| When defrosting |

| Extra time channel |

Preheater enabled in defrosting mode

Type of feedback

| None | Alarm | Run Indication |

The alarm "AL-186 Malfunction preheater" is triggered if the feedback related DI is tripped

Digital start output

| No | Yes |

| Yes with flow interlock |

"Yes with flow interlock" - The electric heater can only be activated if the supply air fan is running (min flow for indication is reached)

Preheater output when recirculation/support

| 0% | 100% | Auto |

Preheater output min limit

[0] %

Preheater output max limit

[100] %

Preheater output when the unit is stopped

[0] %

Configure inputs

Configuration > I/O allocation settings >

Analog inputs > Preheater temperature

Any available I/O

Temperature of the preheated air

Digital inputs > Feedback preheater

Preheater control

Digital outputs > Preheater start

Analog outputs > Preheater

PID Settings

Configuration > PID controllers > Preheater


[33] oC

PID settings


[100] s


[0] s

Start with output

[0] %

PID regulator starting point for the faster reach of the setpoint value

Operational settings

Data & Settings > Temperature control > Preheater

Setpoint preheating

[-15] oC

The desired minimal temperature after preheater

Graphical representation


 87% - preheater output

-15.7 oC - temperature of the preheated air