Series fan powered VAV boxes remain on when unoccupied on a CCP III system

Issue:

Series fan powered VAV boxes remain on when unoccupied on a CCP III system

Resolution:

To allow fans on series fan powered VAV boxes to stop when UCM is unoccupied, Set the "Enforce Minimums While Unoccupied" to Disabled. This setting is found under 'CCP Group Editor' in CCP PC software under Setup in the main menu. This allows all VAVs in the selected group to go closed when unoccupied and fans to shutoff.

If the CCP is unoccupied when the 'enforce to minimums while unoccupied' is set to Disabled, the serial fans my continue to run even though the damper shows 0% position. Cycle CCP to occupied, then back to unoccupied to cause VAV boxes to shut off serial fans.

Regarding the "Bypass Duct Press Sens Fail" diagnostic, when the CCP goes unoccupied, the CCP initiates calibration. During this sequence, the static pressure sensor needs to find zero air flow at the communicating bypass damper assembly. If fans are running in VAV boxes, air flow could be induced across the sensor and a diagnostic can be generated.

When VAV UCM control mode is unoccupied, unoccupied cooling and heating temperature set points are used for temperature control. The UCM uses series fan and heat necessary to maintain the current unoccupied set points. On electric heating and hot water heating units, the fan and heat are energized at the unoccupied heating set point. The minimum cooling flow set point is reset to zero unless minimums are being enforced by CCP setting "Enforce minimums while unoccupied" enable/disable selection is ENABLED, found under Group editor for each group.

If you have a fan that runs continuously, you must select disabled for this setting; "Enforce minimums while unoccupied", otherwise you will get "Bypass duct press sens fail" alarms.

This means the VAV UCM maintains minimum occupied damper position even when unoccupied. Since air valve dampers are open, the series fan continues to run. A series fan is energized anytime the air valve damper position is greater than 0%.

 

Notes:

 

Changes:

 

Other Question/Problem/Cause Statements:

• Series fan powered boxes when in unoccupied mode never shut off on a CCP III
• Why don't CCP III Series fan powered box fan will shut off when unoccupied?
• "Bypass Duct Press Sens Fail" diagnostics in Alarm log on Tracker coming from CCP III
• Series fan powered VAV boxes remain on when unoccupied on a CCP III system

Facts:

• VariTrac III Central Control Panel (CCP)

Original wave: wave1005