Component redundancy: fan arrays
The new strategy for AHUs is to replace large, old style, belt driven centrifugal fans with an array of smaller and simpler EC RadiCal and Plug fans from ebm-papst as shown in the picture below.
Available in spider mount arrangements, the use of an array of plug fans has a range of advantages:
- Space reduction and reduction in size of air handling unit
- Greater energy efficiency and better even airflow through the unit and cooling coil
- Lower maintenance costs
- Greater redundancy
(J Domholt; Using Fan Arrays. www.govenergy.gov; Providence Aug 2009.)
- Space reduction. Due to the lack of belts and drives mounted along a horizontal mounting, typically 30% of the length of the fan chamber can be saved when spider mount arrays are used.
- Better efficiency. EC backward curved centrifugal fans typically save up to 50% power when compared to similar forward curved belt-driven fans. Simpler airflow through the air handling unit corresponds to drops in total pressure and further reduces the power input of the system.
- Lower maintenance costs. Moving to direct drive systems reduces the need for belts and bearings to be changed. The spider fan mount uses completely balanced fans and this in turn reduces the mechanical stress in the system. As can be seen in the image above, it is not unusual that NO anti vibration mounts are needed.
- Greater redundancy. Often single fan units are replaced with an array of products, therefore providing for greater redundancy in the system. The EC plug fan array is speed controlled either through an external system or using in-built intelligence such that the speed of the array can change to compensate if a single failure occurs.
With greater impeller efficiencies than ever before, the new EC centrifugal fans are being continually matched to simple digital control systems to allow the maximum performance to be realised. For instance, the ebm-papst Carel Universal Gateway allows simple communication from most building control systems e.g. BACNET, to ebm-papst MODBUS centrifugal fan array products.
The simple benefit of this type of system provides the right amount of control which in turn ensures that the air-movement product is doing what is expected while also monitoring the power consumption and status of the fans.
“This simple two wire control which does not require complex installation is the easiest way to get complete performance control” said Simon Bradwell. “Many end users are now seeing the cost and performance benefits that can be achieved using this technology, especially where detailed power control and performance monitoring is going to be required.”