Late last year, a northern New Jersey hospital was experiencing issues with an old centrifugal fan with an external 30-hp motor inside a 30,000 CFM air handler that served patient floors. Among the fan’s problems were noise, vibration, inrush current at startup, and it was a huge energy hog. Fan replacement was being seriously considered.
A few months after tentatively reaching out to MSC about replacing the fan, there was a catastrophic bearing failure. A temporary repair was quickly rendered, and with the fan now limping along, replacement rapidly became a priority. Working with a local custom fan and coil contractor, MSC proposed replacing the old constant-speed centrifugal blower wheel with a new fan array system, and we were promptly awarded the project.
Fan Array Benefits
Retrofitting the system with a fan array offered many benefits to the hospital. As opposed to the original fan’s constant speed, a fan array is comprised of multiple variable-speed, electronically-commutate motors, or ECMs. CFM and static pressure are more easily controlled, and redundancy improves system reliability; if one fan fails, the other fans automatically pick up the slack to allow the system to run at 100%. A single failed fan can easily be replaced by one or two technicians, much unlike single centrifugal fans. Fan arrays are more energy efficient, quieter, and run with less vibration than the single centrifugal blower. With no drive belts to tighten or replace, less maintenance would be required.
In order to pull off the trick of getting the large centrifugal fan out of the air handler and the new fan array in, MSC had to perform our own brand of surgery by cutting a passageway in the air handler’s exterior. This opening was later sealed and made tight at the end of the project. MSC next disconnected, removed, and scrapped the original fan, motor, and hot water coils. The new fan array was installed quickly and easily, with boxed fans stacked in parallel, along with new hot water heating coils. The system was commissioned and tested, fan-by-fan and as a whole, including failure scenarios.
The hospital was entirely satisfied with its new variable-speed fan wall system and is now exploring where they can incorporate fan arrays elsewhere in their facility.