Hunting Rule

Type: hunting — Built-in check; no custom expression.

What the rules engine does

The hunting rule flags which is defined by ASHRAE Guideline 36 Fault Rule Four is excessive operating state changes — when the AHU cycles too rapidly between heating, economizer, and mechanical cooling modes. This is often caused by PID tuning issues (hunting). The engine builds an operating-state vector from economizer damper, supply fan VFD, heating valve, and cooling valve. It counts how many state changes occur in a rolling window. When the sum exceeds delta_os_max, a fault is flagged.

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excessive_ahu_state_changes (hunting)

Excessive AHU operating state changes (PID hunting).

name: excessive_ahu_state_changes
description: Excessive AHU operating state changes detected (hunting behavior)
type: hunting
flag: fc4_flag
equipment_type: [AHU, VAV_AHU]

inputs:
  Damper_Position_Command:
    brick: Damper_Position_Command
    column: economizer_sig
  Supply_Fan_Speed_Command:
    brick: Supply_Fan_Speed_Command
    column: supply_vfd_speed
  Heating_Valve_Command:
    brick: Valve_Command
    column: heating_sig
  Cooling_Valve_Command:
    brick: Valve_Command
    column: cooling_sig

params:
  delta_os_max: 10
  ahu_min_oa_dpr: 0.1
  window: 60

---

Next: OA Fraction Rule