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It is, the emergency heating or cooling that is triggered for a zone if the zone breaches the building limits. However, the resultant conditioning is always based on the mode at which the system level equipment is functioning in, that is 'in the direction' of mode at which the AHU functioning . E.g. if the AHU is in heating mode, then if any one of the zones breaches the building minimum temperature, it will cause emergency heating only to turn on, but if the zone breaches the building maximum temperature then the emergency cooling condition AHU is in heating mode. This ensures that false sensor readings do not cause the system to turn on.
If the temperature in a space continues to drop in the example above, it would ultimately go below zone temperature dead leeway and the zone would be marked dead. This would cause the emergency heating to turn off.
The switching over of the mode at which the AHU is operating is based on the profile the AHU is running on (VAV/DAB). A VAV always favor cooling mode even if one of the zones needs cooling.
|Building Breach and Zone dead Temperature Illustration
|Temperature Breach Emergency Conditioning Illustration
The temperature breach for emergency conditioning is usually pre defined value when a CCU is configured, CCU is the system level device that controls and monitors the building level equipment.
The predefined value of temperature limits for the building breach conditioning is viewed in building section in the Installer options screen as below.
And the temperature limits for the building breach condition can be edited from the master control for the temperatures from the CCU as below.
For more information refer to CCU Master Control