By the late 19th century belt driven fans which where powered by water wheels had been introduced. These fans worked by attaching wooden or metal blades to the shaft which was driven by a belt to work the machinery.
By 1832 the first ventilation fan had been invented by Alexander Sablukov. His invention was named as centrifugal fan, air pump. The centrifugal fan was deemed a success after it had been used in coal mines and factories in 1832-1834.
The electrical fan was produced by Thomas Edison and Nikola Tesla in the late 19th century early 20th century these fans where developed for public use.
The desk fan was produced by Dr. Schuyler Skaats Wheeler in 1882 this fan was sold by American firm Crocker & Curtis electric motor company. A few years later the ceiling fan was introduced by Philip Diehl these fans where used in commercial establishments and households.
In the 1920’s steel was able to be produced in a range of different shapes which brought fan prices down allowing them to be more affordable.
- Principle Application of Motorised Ventilation Fan
The ventilation fan main use is to produce airflow which will maintain good air quality, ventilation, exhaust, heating and cooling throughout a building. When deciding which fan and motor to use many factors which have to be considered when selecting the fan such as maintaining good air quality and minimise moisture from occupants, also dust and gases emitted within the building have to be considered.
To expand on this the fan will also be required to produce enough airflow throughout the system to control the temperature throughout the building, this is where the importance of the motor to control these aspects comes in.
When selecting which fan and motor to use all the above aspects need to be taken into account. It is the designer’s job to determine which to use via the manufacturer’s performance data. Based on this data it is possible to select a fan model, the specific model size, and the fan speed necessary to achieve the airflow rates and static pressure rise conditions necessary for the overall air pollution control system, as well as which motor is best suited for the necessary requirements.
Main Components of a Motorised Ventilation Fan
- The Motor
The motor which is used to power a ventilation fan can be a D.C motor or a three phase induction motor. These motors take Electrical energy and convert it into Mechanical energy as illustrated in the operation of a D.C motor (figure 1) and described below.
Figure 1. Operation of a D.C Motor
- D.C Motor – Is a low voltage motor which can be 24V, 12V or 5V. They are most typically brushed or brushless motors. By referring to figure 1 and 2 it can be explained that when an electric current is applied to a coil the motor creates a magnetic flux, which in turn produces a torque (measured in RPM; Revs Per Minute) and allows current to flow through the field windings. These windings (or coils) are connected so that alternate north and south poles are produced. The field windings are wound around laminated and riveted pole pieces, or cores. The brushes which are connected to positive and negative terminals will connect with different halves of the commutator ring once the coil has rotated 90º which will reverse the direction of current flow.
Figure 2. Cut away of a typical D.C Motor
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Three-phase induction motor – Is powered by a mains voltage. By referring to figure 3 it can be explained that a rotating magnetic field is produced by connecting a three-phase supply to stator windings. Current in the stator windings set up an air-gap travelling-wave magnetic field of almost constant magnitude and moving at synchronous speed. In turn the field cuts the rotor conductors at slip speed which induces a corresponding e.m.f (electro motive force) and causes current to flow in the short-circuited windings.
As stated in Lenz’s law “An induced current is always in such a direction as to oppose the motion or change causing it", this in essence means that the interaction of these currents with the travelling-wave field produces a torque to turn the rotor in the direction of the field. The magnitude of the current depends upon the slip and on the impedance of the rotor windings.
Figure 3. Cut away of a 3-phase induction motor
- The Blades
On a centrifugal fan there are three different types of blades formation supplied with the fan, these include:
- Forward-Curved: Blades are curved in the same direction in which fan rotates. Forward-curved is most commonly used on high pressure rise systems meaning a smaller fan size that runs at reduced RPM. This in turn reduces the noise and dominant frequencies.
- Backward-Curved: Blades are curved in opposite direction of which fan rotates. These blades are used on a system running at lower pressure than the Forward-curved. To achieve the given duty backward-curved blades have to rotate at twice the speed of forward curved which can result in noise and mechanical problems. Best used on systems with varying volumes as efficiency can be maintained better.
- Radial: Blades are straight out from hub. These blades are more commonly used within the industrial field where particles will be flowing within the blades as the blades are least sensitive to solids building up.
Figure 4. Three types of blade formations
- The Controls
The ventilation fan is commonly controlled by a constant speed drive or a two speed drive. The constant speed drive works by only allowing air to be supplied to the building at the rate it of its initial setup. The two speed drive works by allowing air rate to be changed to suit the requirements of the building. Typical situations that could arise are a change in the number of occupants, leading to rooms being required to heat up or cool down.
Ventilation controls are easy to include in the specifications of a new project. Like the thermostat, these controls are designed, installed and commissioned by the HVAC contractor.
5.0 Applications of the Motorised Ventilation Fan
Typical applications of the motorised ventilation fan are found in systems which include removing dust in the air, drying, climate control (air conditioning), cooling systems and ventilation systems.
The motor itself can either be stand alone or integrated. For integrated applications these would commonly be found in cars, large cooling systems and winnowing machines.
6.0 Safety Devices
All motorised ventilation fans are fused by a circuit-breaker in order to not only comply with British Standards but to prevent damage and fire. The breaker works by detecting a fault condition when there is current that exceeds the maximum current carrying capacity and cuts the power supplied to the motor.
Thermistors are used to prevent the motor from overheating. A thermistor is a type of resistor which works as a temperature detector that opens the contacts which disconnects the power to the circuit if the motor overheats and prevents the spread of fire.
The fan will come with a protective guard to stop users from being able to touch the mechanical parts such as the blades which could lead to serious injury and the motor is encased in a metal shell as illustrated in figures 1 and 2.
7.0 Future Developments
The motorised ventilation fan could be supplied and operated via solar panels which have the advantages of having no toxic fuels and relatively little maintenance, is inexhaustible, and, with adequate financial support, is capable of becoming directly competitive with conventional technologies.
Solar energy is a renewable resource and is converted to electrical energy in two ways. One by using photovoltaic materials which generate an electrical potential when exposed to light or by using a thermal process that uses the energy from the sun to heat a fluid (water) which is then used to provide power, known as (CSP). Also they don’t collect any harmful waste or pollute the environment and after the initial cost to setup is a free source of energy.
A small solar panel setup could easily be used to ventilate a large floor area with a high airflow rate.
Figure 5. Basic operation of photovoltaic solar power
8.0 Conclusion
The ventilation fan is a vital part of any building services design and without the pioneers like Thomas Edison, Nikola Tesla and Alexander Sablukov to name a few we would be ill-equipped to deal with the constant changes in air pressure and temperature as required in buildings today and in the future.
With today’s advances and being able to control the temperature and air quality automatically and/or at the touch of a button makes a building a comfortable place to be. It would be hard to imagine as we normally take the room temperature etc for granted without taking into consideration the technicalities which provide us all with a comfortable environment.
Thanks to modern advances the motors in which we use to power the ventilation fans are far more efficient, cost effective and require little maintenance. Without the use of D.C motors or 3-phase induction motors powering the ventilation fans and being controlled by either a constant speed or two speed drive buildings would be an uncomfortable place to inhabit. They would be overheated, stuffy, dirty and overall they would be very unhygienic places to work.
9.0 Bibliography
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Electrical Circuit Theory and Technology J. O. Bird 1997 (2nd Edition)
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IEE Wiring Regulations 17th Edition BS7671
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Electric Motors and Drives; Fundamentals, Types and Applications by Austin Hughes, 3rd edition (14th Dec 2005)
10.0 Appendix
Please see the attached Data Sheets for manufacturer’s details on their products which include:
- Activair single-phase ventilation fan
- Emerson A.C Motors
- Marathon Electric HVAC, A.C, D.C and variable speed Motors
