Air Horsepower |
The work done by the fan or the power output of the fan. See the Performance Relationships section for more details. |
Application Range |
The range of operating volumes and pressures, determined by the manufacturer, at which a fan will operate satisfactorily. |
Blast Area |
The fan outlet area minus the projected area of the cutoff. |
Blocked Tight Static Pressure |
The operating condition in which the fan outlet is completely closed resulting in no air flow. |
Brake Horsepower |
The actual horsepower a fan requires or the power input of the fan. |
Drive Losses |
The power used to overcome belt, pulley, and bearing friction. |
Fan Static Pressure |
The total pressure minus the fan velocity pressure, also the static pressure at the fan outlet minus the total pressure at the fan inlet. |
Fan Total Pressure |
The difference between the total pressure at the fan outlet and the total pressure at the fan inlet. |
Fan Velocity Pressure |
The pressure corresponding to the fan outlet velocity. |
Free Delivery |
The operating condition of maximum fan delivery at which static pressure across the fan is zero. |
Mechanical Efficiency |
The ratio of power output to power input, also referred to as total efficiency. |
Outlet Area |
The inside area of the fan outlet. |
Point of Operation |
The cfm-pressure requirements for a given application. |
Standard Air |
Air at a temperature of 70oF dry bulb and a barometric pressure of 29.92 in. of mercury and a barometric pressure of 0.075 lbs/cu. ft. |
Static Efficiency |
The efficiency based on static air horsepower. See the Performance Relationships section for more details. |
Tip Speed |
The circumference of the fan wheel times the RPM of the fan, expressed in ft/min, also referred to as peripheral velocity. |
Axial Fans |
Axial fans can be categorized into three major varieties, distinguished by the applications for which they are designed rather than by blade configurations. The principle types of axial fans are propeller, tubeaxial and vaneaxial fans.
Because the discharge opening is inline with its entrance, and axial flow fan offers the advantage of simplified duct arrangement. This become important when space considerations must be taken into account. |
Centrigual Fans |
Centrifugal fans can be categorized into three major varieties, distinguished by the blade curvature. This curvature of the blades determines the performance characteristics of the fan. The following figure shows the three types of centrifugal fan wheels commonly used, with a vector expression of air leaving the blades.
Whether a forward curved or backward curved blade fan is to be used is determined by fan size as well as the particular application. Size for size backward curved blade fan will generally require less horsepower than a forward curved blade fan for a given application. Despite the higher speed required for a backward curved blade fan they are as quiet or quieter than a forward curved fan, when properly selected. These factors generally make backward curved blade fans a logical selection for large application (generally greater than 24 inch diameter wheels). Due to the high speed of backward curved fans the belt speed may be excessive in the smaller applications. In these applications, the lower speed characteristics generally make the forward curved blade fan more desirable. In addition, the lower speed is quite adaptable to packaged central station units having more than one fan on a common shaft, due to the required shaft sizing. |
Fan Efficiency Analysis Tools (FEAT)
Are fans or blowers installed that are not sized correctly for the task?
Are fans or blowers being throttled in order to control the flow rate?
Is bypass control being utilized to vary the flow out of the fan or blower?
Does the facility have a cooling tower(s)?
Does the facility utilize high or low pressure blowers to convey material?
Does the facility have more than one baghouse and multiple distribution lines feeding into these baghouses?