The fail-safe function ensures continuity of AHU operation if malfunction of pressure transmitters or supply temperature sensor occurs.

In the fail-safe mode, control of the fan and sequence is overridden with the manual output. The mode can only be active during scheduled run period and in absence of critical alarms (e.g. Freezing protection, Fire alarm). The AHU returns to normal operation once connection to the faulty sensor is restored.


In case of malfunction of the supply air temperature sensor (AL146) the fail-safe mode can override output of Heating or Cooling sequences. It also overrides all the sequences of the higher priority to the max output.

e.g. fail-safe is configured to set the 3rd Heating sequence to 50% in case of sensor malfunction. This means that the heating sequences will be set accordingly:

1st heating sequence "Heating 1" = 100%

2nd heating sequence "Heating 2" = 100%

3rd heating sequence "Heating 3" = 50%


The fail-safe mode is indicated by the alarm AL241 Fail-safe airflow/temperature control.


Manual output of the supply air fan can be triggered by:

AL153        Sensor error pressure supply air        (if Pressure is set as fan control type)

AL155        Sensor error flow supply air        (if Flow is set as fan control type)


Manual output of the extract air fan can be triggered by:

AL154        Sensor error pressure extract air        (if Pressure is set as fan control type)

AL156        Sensor error flow extract air        (if Flow is set as fan control type)


Manual output of the sequence can be triggered by:

AL146        Sensor error supply air temperature


Configuration example of fail-safe mode







Variable

Available options & Selection

Note






Activate Fail-safe mode





Configuration > Functions > Function activation





Fail-safe mode

| No | Yes |

-






Enable fail-safe for the alarms





Configuration > Alarms > Manual operation and warnings > 146 Sensor error supply air temperature





Action

… | Fail-safe mode |

-









Configuration > Alarms > Manual operation and warnings > 153 Sensor error pressure supply air





Action

… | Fail-safe mode |

Can also be set for AL155









Configuration > Alarms > Manual operation and warnings > 154 Sensor error pressure extract air





Action

… | Fail-safe mode |

Can also be set for AL156










Configure manual outputs in Fail-safe mode





Configuration > Functions > Fail-safe mode





153 - Sensor error pressure supply air


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Set fail-safe manual output of the SAF





Supply air fan output in fail-safe mode





154 - Sensor error flow extract air


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Set fail-safe manual output of the EAF





Extract air fan output in fail-safe mode





146 - Sensor error supply air temperature


| Off | Heating 1 | … | Heating 10 |

Select and set Fail-safe manual output of the sequence.

Heating 1 - 1st heating sequence

Heating 2 - 2nd heating sequence





Supply air temperature control in fail-safe mode - Heating





Output in fail-safe mode

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Chapter info                              

Last reviewed: 09/12/2021

Access version: 4.6-1-00 (3068)