An Automated NSW Smart Solutions Guide
Publish Date: 03/12/2026
Redundant VFD Designs for an ACH580
Datacenter, hospital, and biopharma facilities run mission-critical air handling systems where downtime is not an option. Many redundancy designs add enough complexity that they introduce more failure modes than they eliminate. The redundant VFD configuration used on some Huntair (by Nortek) air handlers adds redundancy without the added complexity.
Typical Design
In a standard fan wall installation, a single VFD drives the motors and takes a control signal from the BMS. The BMS runs the control loop, comparing a sensor input against a setpoint and adjusting the VFD output accordingly.
When the VFD faults, the fan wall stops. When the BMS loses communication or the controller faults, the VFD runs at its last commanded speed or falls back to a fixed default. When a sensor fails, the control loop loses its feedback and the BMS can no longer regulate to setpoint. Any of these failures requires manual intervention to restore normal operation. 
The Redundant VFD Design
A primary ACH580 VFD drives the fan wall and fails over automatically to a secondary ACH580 on a fault output. Each drive runs its own internal control loop with duct static pressure or airflow sensors wired directly to the VFDs. The BMS delivers a networked setpoint to both drives rather than running the control loop itself.
A fault on the primary VFD triggers automated switchover to the secondary without any action needed by the BMS. A sensor failure affects one input but does not take down the drive or the control loop. A complete loss of the BMS controller leaves both drives running to their last received setpoint until communication restores. In each case, the air handler keeps running through the event. By configuring the VFD HMIs to display current setpoint against actual value, operators will have immediate visibility into drive state without relying on the BMS.
Benefits
This configuration provides high-availability operation without a significant increase in design or installation complexity. The addition is a second VFD and sensor wiring back to each drive. There is no bypass panel, no custom control logic, and no change to the BMS integration beyond setpoint delivery. A single sensor, a VFD fault, or a full BMS outage does not interrupt the air handler for longer than the automated switchover takes to complete.
Your critical processes require precise, reliable environmental control across temperature, humidity, air pressure, and flow. Our team designs, installs, and maintains control systems tailored to those requirements. Call us to discuss your current environment.