Recirculation is a function for distributing the air in the room using the supply air fan. The function can be used even when there is no heating or cooling demand.

When using recirculation control, the extract air fan stops (but can also be set to run) and a recirculation damper opens which allows the extract air to circulate back through the unit.


Recirculation is activated either via a digital input signal or by connecting it to the "Extra time channel 4" schedule:

  • If a timer output for Low/Normal/High speed is activated during recirculation via Extra time channel 4, Low/Normal/High speed gets priority.
  • If a timer output for Low/Normal/High speed is activated during recirculation activated by a digital input, recirculation gets priority.


Recirculation damper actuator can be connected either to a digital output or a modbus actuator.


Recirculation control can be configured as either air circulation (temperature control inactive) or air circulation with temperature control (only heating, only cooling or both heating and cooling).


Recirculation control has its own setpoint. However, the other settings are the same as for normal operation. e.g. if normal operation has been configured as room control, room control will also be used during recirculation.


The recirculation setpoint can be configured as constant or offset. Constant means that the recirculation setpoint will be used. Offset is based on an offset from the supply air setpoint.


To lower the temperature, it is possible to configure free cooling to be used during recirculation.


A max. room temperature can be configured for recirculation control. If the room temperature rises above the set value, recirculation will be stopped. When the

room temperature has fallen 1 K below the set max limit, recirculation will start again if the start conditions are still present.


It’s possible to configure the output value for each sequence when recirculation is active. The output can be configured to 0%, 100% Or Auto.

e.g. It is common that operation of the exchanger is not required during recirculation. In that case it can be suspended by settings Sequence output during recirculation to 0%.


During recirculation, the fan runs on "Normal" fan level. The level can be adjusted by the fan offset value.

e.g. The default setpoint for "Normal" fan level is 50% (manually control type). The speed can be reduced by entering a negative offset value: 50% (Normal setpoint) -10% (Offset) = 40% fan level during recirculation.


Configuration of the Recirculation





Variable

Available options & Selection

Note





Activate function




Configuration > Functions > Function activation >




Recirculation

| No | Yes |






Configure function




Configuration > Functions > Recirculation




Enable supply air temperature control when recirculation running

| No temperature control |

| Heating + Cooling |

| Heating | Cooling |

Enabling /disabling of heating/cooling sequences during recirculation




Enable the night cooling function when recirculation

| No | Yes |

Free cooling function




Use extra time channel 4 to start recirculation

| No | Yes |

Enable scheduled recirculation







Run extract air fan during recirculation

| No | Yes |




Fixed setpoint or setpoint offset when recirculation run

| Fixed setpoint | Setpoint offset |

Choice of temperature control method






Recirculation settings for sequences


Configuration > Functions > Function activation > Heating/Cooling sequence setup > SEQ-X



Sequence output when recirculation/support

| 0% | 100% | Auto |

0% - minimal output

100% - maximal output

Auto - regulated by the supply controller




Allocating IOs


Configuration > I/O allocation settings > Digital outputs


Digital inputs > Start/(Stop) recirculation

Any available I/O



Digital outputs > Recirculation air damper

Control signal to hardwired actuator.

The DO can stay un-allocated for modbus type actuator.

Configuration of modbus actuator



Operational settings


Data & Settings > Demand control > Recirculation


Setpoint recirculation

[18.0] oC

Setpoint for configured temperature control mode or Offset for the supply temperature setpoint


Setpoint offset recirculation

[0] oC



Change to outdoor air when room air >

[25] oC




Outdoor air damper opened

No | Yes

Indication of the outdoor air damper



Data & Settings > Fan control > Fan setpoints



Offset supply air fan when recirculation

[0]

Adjustment of normal fan level during recirculation



Offset extract air fan when recirculation

[0]




Scheduled operation



Time settings > Schedule > Extra time channel 4




Monday … Sunday, Holiday

Start [00:00] … Stop [00:00]

Only if scheduled run has been activated





Graphical representation




Flowchart > Recirculation damper





Indication: Open / Closed





Related topics:

Air quality control