Advantages of Variable Speed

Advantages of Variable Speed: 

Variable-speed blower motors are designed to provide greater comfort through reduced initial air velocities and noise. When the unit first turns on, the blower operates at low speed, which not only provides less noise than a single-speed blower, but also allows the compressor and coil to ramp up before the unit begins moving large volumes of air through the system.

Most motors are designed to operate at a constant speed and provide a constant output. While in many cases this may be more than adequate, it is not in all. Two-speed induction motors can improve efficiency for refrigerators, air conditioners, and blowers.

Although in theory this can be done with any induction motor application, a greater value is obtained with appliances that run frequently. With a two-speed mode of operation, long time periods that would normally use full power can be replaced by long periods of substantially less power with short periods when full power may be needed.

Currently, residential central air conditioners, blowers (furnaces), and clothes washers take advantage of this technology since small changes in speed can drastically cut down on power usage (power consumption is approximately proportional to the cube root of shaft speed, e.g., a shaft reduction of 10% corresponds to at 27% reduction of power).

Propeller Fans

Propeller Fan:

A propeller is a type of fan that transmits power by converting rotational motion into thrust. A pressure difference is produced between the forward and rear surfaces of the airfoil-shaped blade, and a fluid (such as air or water) is accelerated behind the blade. 

The propeller fan sometimes called as PANEL FAN, is the most commonly used of all fans. It can be found in Industrial, Commercial, Institutional and Residential applications. It can exhaust hot and contaminated air or corrosive gases from factories, welding shops, foundries, furnace rooms, laboratories, laundries, stores or residential attics or windows.

Sometimes several propeller fans are installed in the walls of a building operating in parallel and exhausting the air.

Propeller dynamics, like those of aircraft wings, can be modelled by either or both Bernoulli's principle and Newton's third law. A marine propeller of this type is sometimes colloquially known as a screw propeller or screw, however there is a different class of propellers known as cycloidal propellers - they are characterized by the higher propulsive efficiency averaging 0.72 compared to the screw propellers average of 0.6 and the ability to throw thrust in any direction at any time. Their disadvantages are higher mechanical complexity and higher cost

Types of Fans used in Construction.

Generally there are 6 types of fans used in Mechanical Construction.

1. Axial Flow Fans:

There are four types of axial-flow fans. Listed in the increasing order of static pressure.

They are:

a. Propeller fans(PFs).

b. Tubeaxial fans(TAFs).

c. Vane axial fans(VAFs).

d. Two Stage Axial Flow fans.

2. Centrifugal Fans:

There are six types of centrifugal fan wheels in common use. Listed in the order of decreasing efficiency, They are:

a. Centrifugal fans with AirFoil(AF)blades

b. Centrifugal fan with Backward Curved(BC) blades.

c. Centrifugal fan with Backward Inclined(BI) blades.

d. Centrifugal fan with Radial Tip(RT) blades.

e. Centrifugal fan with Forward Curved(FC) blades.

f. Centrifugal fan with Radial blades(RBs).

3. Axial Centrifugal Fans.4. Roof Ventilators.5. Cross Flow Blowers.6. Vortex Regenerative Blowers.