High duct static pressure shutdown protections shall be provided on any variable air flow system or any system with automatic dampers where the following are true:
a. The fan maximum static pressure than can be developed at full speed exceeds the pressure rating of the ductwork, plenum or duct accessories. This consideration shall assume pressure control loops are inactive and the fan is at maximum speed and/or normally interlocked dampers have failed in a closed position.
b. The system is subject to surging
c. The system has other special pressure protection requirements
High pressure shutdown protections shall be hardwired to shutdown required fans as required to protect the system. Other devices, such as dampers, valves, speed control signals, may be positioned via the Bilding Automation Systsem (BAS) system signals upon detection of this type of shutdown.
The BAS control system shall have a dedicated high pressure shutdown input to detect the status of the high pressure shutdown controls. When the BAS system detects a high pressure shutdown alarms shall be generated and the BAS shall position valve, damper and fan signals to match the hardwired shutdown positions.
The high pressure shutdown protection shall not override freeze protection controls
The high pressure shutdown shall require a manual reset by the operator.
On fans with isolating dampers in line, where the deadheaded pressure of the fan may exceed the isolation damper pressure rating, fans shall be interlocked with the position of the damper. The interlock shall prove the isolating dampers are open prior to allowing the fan to start. The use of a time delay to delay fan start up after the damper is commanded to open shall not be used.
Guidance: In some cases it may be necessary to provide this type of interlock on larger fan systems, even though the dead head pressure does not exceed the isolation damper pressure rating