22 Jul 2024


How VSDs can make multi-fan HVAC systems resilient

Multi-fan HVAC configurations can help to improve redundancy and reduce reliance on any single fan motor. Oliver Woolley, ABB’s key account manager for HVAC in the UK, explains how VSDs can improve system resilience and reduce wear and tear, while ensuring that a building’s airflow requirements are met.

Part L of the 2010 Building Regulations sets standards for energy performance of new and existing buildings, and in particular that air-handling systems should not consume more electrical power per unit air volume at lower flow rates than they do at 100% design flow rate.

While this clearly precludes the use of dampers to control air flow, controlling multiple fans from the same VSD means this VSD must be able potentially to run all of the fans at full power at the same time, necessitating a much larger and more powerful drive. Moreover, a single drive arrangement could also possibly leave the whole system out of action should the drive fail or a fault occur.

Using a smaller VSD to control each fan motor improves redundancy and ensures each fan is operating at optimal efficiency. Furthermore, using VSDs with built-in peer-to-peer functions to implement load-sharing avoids the need for PLC control to manage demand, balance run time between each individual fan, and keep all fans running optimally.

In a peer-to-peer configuration, one drive acts as a master, and the remaining drives act as follower drives. Should the master drive fail, master status can be transferred automatically to a follower drive according to a pre-defined priority.

In normal operation, if the active fans cannot meet the required demand, the master drive will automatically start additional fans in the configuration, one by one. Similarly, if demand reduces, the master drive will automatically stop active fans to keep the load balanced between the remaining fans, while also ensuring they are running at optimal efficiency.


If you have any questions about configuring multi-fan HVAC systems or using VSDs in HVAC applications more generally, you contact Oliver Woolley at oliver.woolley@gb.abb.com.