Fan Determination (VAV Parallel Flow Based) - Johnson Controls - Metasys - LIT-12011147 - Software Application - Controller Configuration Tool - 13.1

Controller Tool Help

Johnson Controls
Product name
Controller Configuration Tool
Document type
User Guide
Document number
Revision date

This module generates the on or off state for the control of a parallel fan within a VAV application according to a flow based algorithm.

If the unit is in Occupied, Standby or Bypass mode and the flow is less the Parallel Fan Occ Min Flow setting, the state output is on. Additionally, if the heating or cooling command are greater than the Fan On Threshold, the state output is on. When the heating and cooling command are both below the Fan Off Threshold, the state output is off. If the Heating Purge Duration is greater than zero, the Heating Command must be below the Fan Off Threshold for the time specified before the state output is off.

Note: The VAV with Flow based Parallel Fan application has a default value of zero for Fan Control, which could cause a short cycle condition for the fan motor. To avoid a short cycle condition, view the logic for the module Parallel Fan Determination Flow Based. Select the Less Than block and view details. Change the differential to a value that does cause the fan to short cycle.

This module can be used to provide the on command to single speed fans, three speed fans, or proportional fans.

You can view and modify the modules in this group’s logic.