Which Fans Are Used in HVAC Systems?

The right fan can make a big difference between the operation of heating and cooling systems. There are many different models, but it pays to research before buying one. The wrong type of fan could lead to underperformance and high operating costs due to the lack of efficiency or even more significant problems, such as excessive noise levels from an ineffective motor. There are several types of fans available, and the most commonly used fans found in HVAC systems are:

Axial fans
Forward-curved centrifugal fans
Backward-inclined fans

This article will explain each fan type and its uses, advantages, and disadvantages. In addition, some of these fans come with integrated units like motors and controls to reduce space requirements and simplify maintenance procedures.

Axial Fan

Axial fans suit applications perfectly when they are equipped for jobs that require less static pressure and low airflow. Axial fans have the simplest design, with their blades being attached to the rotating shaft in a propeller shape. Moreover, axial fans are a great choice when airflow is not an issue. They typically have lower noise levels and more reliable performance than other types of comparable products, making them perfect for any application. That being said, it would be best to consider axial fans not suited for high-pressure applications.

Axial fans are the best option for any application that needs airflow, but does not require too much resistance against air movement. These low-cost devices can be used in cooling towers and condenser slots on outdoor ACs or electronic components. While the aforementioned devices require airflow to release their heat, they may fail to do so due to little or no resistance against air movement; hence, low-cost axial fans are required.

Centrifugal Fan

Centrifugal fans are often compared to water wheels or hamster wheels because of their appearance. They consume more power than axial fans, but produce higher pressure rates, making them effective at moving large quantities of air quickly within a confined space. Although typically noisier than axial fans, centrifugal fans can be driven directly or with a belt, and can use variable frequency drives for optimized performance in varying environments.

The use of an axial fan and other incompatible components where a centrifugal fan should reside would result in poor airflow. The air flowing through a system must be able to overcome static pressure, which can be difficult for some fans to handle. As such, centrifugal fans are employed to overcome static pressure inside air duct systems and provide excellent cooling efficiency for HVAC equipment.

Backward Inclined Fans

The backward inclined fan has an unusual blade shape, typically giving the impression that it is installed incorrectly. Backward inclined fans can be classified into curved and straight blade fans, and operated similarly to centrifugal fans. Backward Inclined fans are commonly used in industrial applications requiring high airflow and specific variable resistances, such as in dust collection, cooling, and incineration systems. In addition, commercial HVAC systems sometimes use backward inclined blades for ERV ventilation.

Controlling the Speed of Fans

Fans can change their speed during intermittent operation when total airflow is not required. However, this approach does not work for applications that require controlled and consistent airflow. As most fans cannot change their speed on their own, an external device is needed, such as an electronic remote control or other mechanical machinery. For instance, belt-driven fans are typically equipped with pulleys of increasing diameter to provide several speeds. The same effect can also be accomplished through the use of a gearbox.

Variable frequency drives (VFD) allow the speed of your fan to be modulated with ease. They do this through a controlled change in voltage and current which results in smooth transitions between different rpm values. In addition, variable frequency drives (VFD) and brushless DC motors can modify their supplied voltage to achieve speed modulation.

Multiple-speed motors are an excellent option for open discharge applications with axial fans. Speed control is directly related to airflow as there is no resistance in the airway. However, ducted installations require additional attention because of potential static pressure variations that may need addressing. As such, precise airflow can only be achieved through VFDs.

Conclusion

Overall, the performance of a ventilation system is ultimately determined by the number and size of fans installed. To find the solution fit for your operations, it is recommended to consult with professional HVAC engineers to best optimize your ventilation system for maximum power and load distribution throughout a system. To obtain the parts you need, Industrials Unlimited is an all-inclusive marketplace for top-quality new, used, and obsolete industrial fasteners, in addition to industrial automation tools, and more. With our constantly-growing parts database of over 2 billion ready for purchase items, we are an all-inclusive, streamlined purchasing platform ready to assist you.