![Air flow in a cone shape](https://kumkoniak.com/72.jpg)
The other factors that will affect the fan’s efficiency are the width of the impeller wheel, the clearance space between the inlet cone and the rotating impeller, and the area used the discharge the air from the fan (the so-called ‘blast area’). There are a number of shapes of blades that can make up the impeller, with the main types being forward curved and backward curved – the shape of the blade will determine its performance, potential efficiency and the shape of the characteristic fan curve.
![air flow in a cone shape air flow in a cone shape](https://www.scienceabc.com/wp-content/uploads/2015/12/Winglets-cover-e1449576934528.jpg)
To move more air, the fan can be designed with a ‘double width double inlet’ impeller, allowing air to enter on both sides of the casing.įigure 2: Centrifugal fan in scroll casing, with a backward inclined impeller (Source: CIBSE TM42:2006) The majority of traditional centrifugal fans are enclosed in a scroll type housing (as in Figure 2) that acts to direct the moving air and efficiently convert the kinetic energy to static pressure. These fans are capable of generating both high pressures and high volume flowrates. With centrifugal fans, the air enters the impeller along its axis, then it is discharged radially from the impeller with the centrifugal motion. Manufacturers should also identify preferred ‘safe’ working ranges in their literature. This includes the areas of instability that are due to hunting, where the fan can flip between two possible flowrates at the same pressure or as a consequence of the fan stalling (see Stalling of air flow box). These are exaggerated, idealised curves, and real fans may well differ from these however, they are likely to exhibit similar attributes. Real fans can differ widely from these simplified curvesĬharacteristic fan curves are shown in Figure 1. In addition to these, the ‘plug’ fan (that is actually a variant of the centrifugal fan) has seen rising popularity in recent years.įigure 1: Generic fan curves. Some of the more frequently encountered types of fan used in HVAC are listed in Table 1, together with indicative peak efficiencies that have been collected1 from data published by a range of US and European manufacturers.
![air flow in a cone shape air flow in a cone shape](https://ae01.alicdn.com/kf/HTB143EAaovrK1RjSspcq6zzSXXaf/Universal-76mm-Automobile-Cone-Shaped-High-Flow-Cold-Air-Intake-Mesh-Filter-For-Engine-Car-Accessories.jpg)
Table 1: US and European published peak fan efficiency data for fans >600mm in diameter This article will attempt to include areas that may not typically be in many of the other general sources.
![air flow in a cone shape air flow in a cone shape](https://www.grc.nasa.gov/WWW/K-12/airplane/Images/wdgflow.jpg)
This CPD unit will consider selected aspects of these fans, and to complement the article there is much good-quality detailed material freely available (see list at the end of this article). These two types are themselves split into a number of subtypes that have been developed to provide particular volume flow/pressure characteristics, as well as other operational attributes (including size, noise, vibration, cleanability, maintainability and robustness). The two common fan types used in building services for ducted systems are generically referred to as centrifugal and axial fans – the name deriving from the defining direction of air flow through the fan.
![Air flow in a cone shape](https://kumkoniak.com/72.jpg)