Introduction
Fans are used for many different purposes. The typical ones are:
- Ventilation of rooms in order to maintain a desired indoor air quality
- Exhaustion from industrial processes (e.g. spray painting, welding, melting of metal)
- Drying (e.g. grain drying or spray drying)
- Cooling (e.g. chillers and cooling towers)
- Transport of combustion air (e.g. power plants, waste incineration plants and cement plants)
Basically fans can be divided into the following four types:
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Axial fan
In air handling units for ventilation and/or air condition as well as in many industrial and commercial applications axial fans can be used. Some examples are mining, tunnel ventilation, car park ventilation, applications in explosion hazardous areas and high temperature fans to extract heat and smoke in case of a fire. Normally axial fans are suited for relatively large volumes and relatively low pressures. However, special designed axial fans can provide both high airflows and high pressures. Typically, the efficiency of an axial fan can be very high (Max. 75 - 85 %). |
Photo: Kindly provided by Novenco Building & Industry A/S (ZerAx® axialfan type AZL) |
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Centrifugal fan
Centrifugal fans can be divided into the following three types:
Centrifugal fans with forward curved impeller blades are typically used in air handling units but also in industrial and commercial applications. They should be avoided if possible because of the low efficiency (55 – 65 %). |
Photo: ebmpabst (www.ebmpabst.com) |
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Centrifugal fans with backward curved impeller blades without housing are typically used in air handling units. They have a relatively high efficiency (65 – 75 %). | Photo: Ziehl Abegg (Ziehl-Abegg.dk) |
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Centrifugal fans with backward curved impeller blades with housing are typically used in air handling units, but can also be used for the transport of dust and particulates. The centrifugal fans are preferred before axial fans where high airflow rates and high static pressures are required. They have a very high efficiency (75 – 85 %). |
Photos: ebmpabst (www.ebmpabst.com) |
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Mixed flow fan
In a mixed flow fan the air flows in both axial and radial direction relative to the shaft. Mixed flow fans develops higher pressures than axial fans, but lower than centrifugal fans. Mixed flow fans are typically used in air handling units but also in industrial and commercial applications They have a very high efficiency (Max. 75 – 85 %). | Photo: SOLER & PALAU (www.solerpalau.com) |
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Cross flow fan
In a cross flow fan the air flows in an inward direction and then in an outward radial direction. Stove jacket cooling, thermal storage heaters, wood-burning stoves, overhead projectors, tanning beds, climate control systems and heating units. They have a very low efficiency (20 – 30 %). |
Photo: Ziehl Abegg (Ziehl-Abegg.dk) |
* All pictures used here are for illustration purposes only as sample products typical for individual product category, not necessarily the only representative sample.
Due to high electrical consumption, it is of the highest importance that large fans operate as close to their optimal energy efficiency point as possible. Their design conception must also ensure that a high efficiency rate can be reached to start with. In the European Union the recent Ecodesign Directive sets minimum levels of efficiency for the large fans entering the market.
Total electricity consumption of fans driven by motors with an electric input power between 125 W and 500 kW was in 2012 estimated to 344 TWh per year, rising to 560 TWh in 2020 if current Union market trends persist.
The cost-efficient improvement potential through design was estimated to about 34 TWh per year in 2020, with a projected loss of (aggregate of the 10 ‐ 20% expected loss through non-compliance) of 3,4 ‐ 6,8 TWh.
