In the last article, we discussed how the EC centrifugal fan, in terms of motor design and fan characteristics, is the optimal fan choice for your AHU retrofit. Here, we will explore how the EC centrifugal fan and AC axial fan compare in the following areas: Installation, maintenance and noise emissions. 

Installation

EC centrifugal fan: Due to the centrifugal fan’s compact size, there is no space concern for a multiple fan design in the plenum wall. This ensures minimal turbulence and efficient movement of air, as indicated in the above illustration. 

AC axial fan: In contrast, for the AC axial fan to perform optimally, it should be mounted horizontally. However, this is unlikely to be possible in most existing AHUs due to the large amount of space that it will occupy. Instead, the fan will be mounted vertically, as shown in the above illustration. This configuration will lead to increased turbulence.  

Operational redundancy

EC centrifugal fan: In a multiple fan design, even if one fan fails, the other fans will be able to speed up to compensate for the airflow loss. This means thermal comfort levels of end-users can be maintained. 

AC axial fan: The pitfall of single-fan systems like the AC axial fan is the lack of operational redundancy. The AHU will cease to operate in the event of any component breakdown.  

Maintenance

EC centrifugal fan: EC centrifugal fans have a long lifetime expectancy for the AHU application (approximately 100k hours) and have low maintenance needs (e.g. visual checking). Newer fans may even include predictive maintenance features.  

AC axial fan: Frequent maintenance (e.g. greasing of bearing, tightening of belts, and lubrication of pulley system) is expected for the AC axial fan. 

Noise

EC centrifugal fan: As centrifugal fans can run at a lower velocity to achieve the same amount of pressure, it will not produce as much noise or generate as much heat loss. Also, there is no need for a silencer.

AC axial fan: Axial fans tend to produce lower air pressure. Therefore, it needs to run at a higher RPM. Some installations run above 50hz or higher. Higher velocity implies more noise and heat are generated. This also means that the AC axial fan will often need a silencer, but this will take up even more space that the AHU may not have. In addition, a higher velocity also implies more turbulence. 

Conclusion

In conclusion, the ideal AHU fan is the EC centrifugal fan as its design, features and resulting benefits make it specially suited to moving air through ductwork efficiently. It is the fan to choose for AHU fan retrofits or fan replacements. To support this conclusion, real-life data from an AHU fan retrofit project was collected by a third party. To learn more about this case study, click on the button below.