A fan is a widely used device in HVAC systems that creates airflow and provides the necessary air pressure. Fans are generally divided into two categories: axial fans and centrifugal fans, each of which comes in various types. The selection of the fan type depends on the application, required air volume, needed static pressure, and the dimensions of the installation space. To achieve optimal results, it's essential to use the right fan in the right environment. In the following, we’ll provide a brief and comprehensive overview of all types of fans used in HVAC systems.
Axial Fan in HVAC Systems
Axial fans have blades that rotate around a fixed axis, drawing air parallel to the axis and expelling it in the opposite direction. Mainly, axial fans can move twice the amount of air compared to centrifugal fans with similar motor power. But they usually cannot generate enough static pressure to overcome resistance in narrow ducts. Based on the frame type and blade design, axial fans are categorized into propeller, tube (ducted), and vane axial types, which we’ll explain below, and then discuss the advantages of axial fans.
Axial Propeller Fan
The most common and basic type of axial fan is the propeller fan. It consists of up to 6 long, narrow, twisted blades made of metal alloy or plastic. The blades are connected to a hub and rotate inside a housing. In smaller sizes, the blades are directly coupled to the motor, while larger sizes use belt and pulley systems.
Propeller axial fans are ideal for non-ducted systems or those with minimal ductwork, and they handle high airflow with static pressures up to 125 Pascals. Common uses include wall-mounted exhaust fans, ceiling axial fans, cooling towers, and air coolers.
One downside of this type of fan is its relatively high noise level.
Tube Axial Fan
Tube axial fans, also known as duct axial fans, are similar to propeller fans but come in a cylindrical housing. They have better efficiency due to their aerodynamic blade design and casing structure. These fans are widely used in high-traffic areas, underground parking lots, and tunnels.
Vane Axial Fan
Vane axial fans have the highest efficiency among axial fans. In addition to the cylindrical casing, they feature more blades, which help overcome static pressure more effectively.
This type of fan can also replace centrifugal fans in ducted systems, especially in space-limited installations.
Advantages of Axial Fans
Axial fans have some advantages over centrifugal fans. The boldest advantages of axial fans are:
• Higher speed
• Lower energy consumption
• Greater airflow capacity
• More compact and lightweight
• Lower cost
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Centrifugal Fan in HVAC Systems
Centrifugal fans, as the name suggests, operate by using centrifugal force to move and circulate air. These fans, also known as blowers, are cylindrical and consist of several blades mounted on an impeller. Air enters the impeller and moves to the blades, gaining kinetic energy, and is then discharged at a 90-degree angle under high pressure.
Although centrifugal fans move less air volume than axial fans, they deliver a more stable flow with higher pressure. As a result, they consume more power than axial fans with similar capacity. Due to the enclosed mechanical parts, centrifugal fans are more durable and less prone to damage.
These fans are ideal for situations requiring high-pressure airflow, making them widely used in HVAC systems, especially when ductwork is involved. They are also perfect for air filtration systems due to their ability to overcome resistance caused by air filters.
Centrifugal fans come in various types based on blade curvature and applications. In HVAC, the most common models are forward-curved and backward-curved fans, which we will explain below.
Forward-Curved Centrifugal Fan
This type features blades curved forward, allowing it to move large volumes of air. However, the design may cause dust or debris in the air to accumulate on the blades, possibly disrupting performance. Forward-curved fans operate quietly and with minimal vibration, making them suitable for clean air applications, ventilation, and exhaust systems.
Backward-Curved Centrifugal Fan
In this model, the fan blades curve backward. It is mostly used in HVAC systems to efficiently deliver hot or cold air into rooms while maintaining minimal noise and vibration.
Differences between Forward and Backward Fans:
1. The main difference lies in the blade design: forward blades curve inward, while backward blades curve outward.
2. Forward fans have more blades, allowing them to move more air volume.
3. Forward fans need a lower speed to produce airflow compared to backward fans.
4. Forward fans generally produce a stronger air throw.
5. Backward fans operate more quietly than forward models.
Advantages of Centrifugal Fans
Here are the most prominent advantages of centrifugal fans over axial fans:
• High-pressure airflow
• Lower noise levels
• Greater durability, ideal for corrosive or erosive environments
• Suitable for ducted systems
• Easier maintenance
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Conclusion
In this article, we aimed to introduce the different types of fans used in HVAC systems and hope the provided information was helpful. To explore and compare various fan models and capacities, or to check updated prices, visit the DamaTajhiz website — the first and most reputable specialized HVAC supplier in Iran since 2004, holding 3 valid trade licenses. You can also contact our expert consultants during business hours for advice.
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