The fan is a key component in your HVAC system, so it’s important to understand how different models operate. Across the spectrum, there are variations in efficiency, cost, and audibility, and ultimately, the wrong fan for the job could lead to poor efficacy and higher overheads. Below, we discuss what you need to know about the three principle HVAC fan types: axial, forward-curved centrifugal, and backward-inclined.
Axial fans have the most simple design, with propeller-shaped blades and spinning shaft. These HVAC systems are intended for spaces where the airflow and static pressure is fairly low, and thus, aren’t suitable for applications where there is high resistance, or high static pressure. Common applications include outdoor air conditioning condensers, combustion engine cooling, and electronic component cooling (for example, the fan on a desktop PC is an axial fan). Although these fans are the lowest cost of the three, this is because they’re not suitable for high-pressure environments. For instance, in all the mentioned applications, there is little or no resistance to airflow.
Forward-curved centrifugal fan
This type of HVAC fan looks similar to a hamster wheel or waterwheel, with internal spokes and horizontal bars around the circumference. Assuming the air pressure is comparable, a centrifugal fan will create a higher pressure environment. This consumes additional power and creates more noise, so generally speaking, these fans are only recommended if the space really demands it.
As a component in an HVAC system, the main applications for centrifugal fans are pumping air into air duct systems. Unlike the open-discharge axial fans found in contexts like cooling towers, these fans need to be powerful enough to manage the high static pressure in ductwork. Operation requires a direct drive or a belt, and can also be boosted with a variable frequency drive in particularly demanding applications.
This type of fan is identifiable by the unusual shape of the blades, which to the untrained eye, can look incorrectly installed. These fans also have two further subgroups: curved-blade and straight-blade, and are driven in a similar fashion to centrifugal fans.
The most common applications of these fans are industrial settings with high airflow and changeable resistance. Examples include incineration plants, glass tempering, dust extraction, and process cooling. In commercial systems, these fans are generally used in energy-recovery ventilation.
Consult a professional
The exact model of the HVAC system will depend on the application and the budget. Although centrifugal and backward-inclined fans may be more effective, you have to ask if this is necessary, or indeed, if it meets your exact needs. For instance, if your priority is air quality as opposed to circulation, you may be better off looking into purifiers over HVAC systems.
Amongst the key groups of HVAC fans, there are further shapes and sizes that will help you narrow down your options. At the end of the day, you’ll achieve the best results by consulting a building services professional; they’ll be able to analyse the variables, options, and cost limitations to recommend a solution that suits your needs.