Keedian operations · Standard procedure

AHU fan drive in bypass or faulted — modulation and reset authority lost.

The supply-fan variable-frequency drive is running in bypass or has faulted — the fan runs at full speed regardless of what the static-pressure reset is asking for. Both an energy finding (the reset can no longer save fan energy) and a control-authority finding (the fan can no longer follow the floor's demand): a drive fault, a manual bypass left in place after service, or a tripped protection.

01 Detail

Trigger, action plan, and escalation criteria.

optimization_metric hvac medium essential tier AI: hybrid

Related metric: ahu_fan_vfd_performance
Trigger: vfd_state ∈ {bypass, faulted}
Value drivers: Energy savings Asset lifespan Avoided truck rolls
Preconditions: The VFD's state points (modulating, bypass, fault) confirmed valid at onboarding so a bypass or fault is read reliably; the drive's normal modulating range recorded; the static-pressure reset the drive should be following confirmed so the lost authority is quantifiable.
Human role: Scales by tier — at Essential the customer sees the drive state and clears or services it themselves; at Managed, Keedian Ops surfaces the bypass/fault, distinguishes a clearable reset from a hardware fault, and dispatches; at Optimized, Keedian restores modulation within authority where the condition is a clearable state rather than a hardware failure, with an audit trail. A failed drive is referred for a scoped service.
Action plan: (1) Distinguish the state before scoping — a drive in bypass is often a switch left after service that a technician can clear, while a hard fault is a drive that needs attention; read the fault code where the drive exposes it. (2) Confirm the condition is current and not a momentary event during a power blip or a scheduled test. (3) Quantify the exposure: with the drive at full speed the static reset is inert, so estimate the fan-energy left on the table and check whether the floor is now over- or under-pressurized as a result. (4) Tiered response: at Essential surface the drive state; at Managed triage clearable-vs-hardware and dispatch; at Optimized restore modulation within authority where the state is clearable, with an audit trail, and refer a failed drive for a scoped service.
Escalation: (1) A drive faulted with the fan stopped on an occupied floor → the floor is losing air; direct action. (2) Drives found sitting in bypass across several AHUs → a portfolio energy-recovery and re-commissioning item for the MBR. (3) A drive that faults repeatedly after being cleared → a hardware fault developing; scope the drive before it fails outright.
Prevention: (1) Confirm the VFD state points and the reset the drive should follow at onboarding so bypass and fault are read reliably and the lost authority is quantifiable. (2) Alert on bypass and fault immediately, separately from efficiency degradation, so a lost drive is caught the moment it happens. (3) Keep a per-drive state log so a drive that keeps dropping to bypass or fault is surfaced as a hardware candidate rather than repeatedly cleared.