Generally, fans are used for establishing airflow wherever natural air is not available. So for this purpose, fans are an important part of an HVAC system. However, the construction of fans varies and has different methods of application. Furthermore, there are three types of fans that are primarily used in HVAC systems. In this article, we will get to understand these three types of fans and what they are used for.
These fans are namely:
- Axial fan
- Forward-curved centrifugal fan
- Backward-inclined fan
Before we go further into this article, have it in the back of your mind that ventilation systems in some states are subjected to the Mechanical Code of that particular state. Also that a building can only be licensed for its intended occupancy if every one of its internal systems complies with the state mechanical code. Some fan manufacturers include motor and controls all in one to help reduce space consumption in the home, and ease maintenance.
Axial fans are the simplest in construction. Their blades are arranged in a propeller form around a rotating shaft. The fans are manufactured for devices where the airflow and static pressure are very low. Amongst the three types of fans described in this article, the axial fans are having the lowest cost. Note that this type of fan is not suitable for appliances with resistance to airflow. Some of the suitable applications that are compatible with axial fans are outdoor air conditioner condensers, cooling towers, combustion engine cooling, and electronic component cooling. These mentioned applications need an inflow of air to release heat. Also, they have little or no resistance to air movement.
These types of fans are manufactured to look like waterwheels or hamster wheels. With the same amount of airflow, a centrifugal fan will create a higher pressure than an axial fan, which will consume more energy. The centrifugal fans also generate more noise than axial fans, so their use is only based on demand by the application. This fan can be controlled directly or by using a fan belt. The fan can be enhanced by using a variable frequency drive. In HVAC systems, one of the main uses of centrifugal fans is for air-handling units. This is used for blowing air into the ductwork. Unlike axial fans in cooling towers, the centrifugal fans are constructed to overcome the static pressure of the air duct system. Using axial fans for the work of a centrifugal fan will result in poor airflow.
Backward inclined fans
These fans are known for their abnormal blade shape. The fan structure makes it look like the blades were installed incorrectly. Backward inclined fans can be categorized into straight-blade fans and curved-blade. It can be driven just like the centrifugal fan. These fans are mostly for industrial use. It has high airflow and variable resistance. It can be used for applications like incineration systems, dust collection, glass tempering, and process cooling. Backward inclined fans are used for energy-recovery ventilation (EVR) in commercial HVAC systems.