Air movement is at the heart of everything we do. Our fan heaters, portable air conditioners, industrial dehumidifiers, ventilation fans, warehouse cooling fans, fan coil units and evaporative coolers all rely on the movement of air to achieve their function. With that in mind it’s easy to see why the humble fan is probably THE key component to us, but what do you know about fans? Did you realise they come in a variety of formats? Or different shapes and sizes depending on the specific application? In this section we take a look at fans, where they came from, what they’re used for and the different types.
A fan is a type of powered machine, something used to create flow within a fluid, usually air. A fan made up of two key components; a rotating arrangement of vanes or blades which act on the air and a motor which rotates the blade assembly. The rotating assembly of blades and hub is usually known as an impeller. The entire fan assembly can be contained within some form of housing or case to either direct the airflow or offer protection against objects coming into contact with the spinning fan blades. The vast majority fans are powered by electric motors, and the electric motor is the most prolifically manufactured item in human history, but there other sources of power may be used.Hydraulic motors, handcranks, internal combustion engines, and even solar power have all been used to power fans to greater or lesser extent.
Mechanically speaking, a fan can be any revolving blade or blades used to stimulate a flow of air. Different applications require specific airflows and therefore different types of fan. Some fans produce high volume air flows with low pressure (although higher than ambient pressure), whereas some others will produce low air flows but at higher pressures, although this is usually the realm of compressors which specialise in delivering high pressures at a comparatively low volumes. A fan blade will often rotate when exposed to an air fluid stream such as wind, and devices have been developed to take advantage of this characteristic; think windmills, anemometers and more recently, wind turbines for renewable energy sources. The blade profiles used on these applications are very often similar to that of a fan.
Typical applications include for electric fans are climate control and personal thermal comfort (e.g. as pert of an industrial electric fan heater, warehouse fan, floor fan), vehicle engine cooling systems (e.g., in front of a radiator), machinery cooling systems (e.g., the little fans inside computers and/or audio power amplifiers), ventilation, fume extraction, winnowing (e.g., quite literally separating the wheat from the chaff), vacuum cleaners, drying (usually in combination with a heat source or refrigeration system such as a commercial dehumidifier).
One of the most persistent misconceptions about fans is that they cool air when in fact they don’t, they simply move it. While fans are often used to cool people, they do so by exaggerating the effects of the process of sublimation of sweat and increased heat convection into the surrounding air due to the airflow from the fans. A fan blade is generally made of either wood, plastic, or a metal such as aluminium.
The history of fans takes us to ancient India and something called the punkah,which was a primitive type of fan used from circa 500 BCE. This handheld device was made from bamboo strips or other similar plant fibre and could be rotated or fanned to move air. During the Raj period, the word came to be used by Anglo-Indians to mean a large swinging flat fan, fixed to the ceiling, and pulled by a punkawallah, a colloquial name for a servant.
For purposes of air conditioning, the Han Dynasty craftsman and engineer Ding Huan (fl. 180 CE) invented a manually operated rotary fan with seven wheels that measured 3 m (10 ft) in diameter; in the 8th century, during the Tang Dynasty (618–907), Chinese engineers started using hydraulic power to rotate the fan wheels for an early form of air conditioning, while the rotary fan became even more common during the Song Dynasty (960–1279).
In the 17th century contemporary scientists such as Otto von Guericke, Robert Hooke and Robert Boyle established the basic principles of vacuum and airflow through various experiments. The English architect Sir Christopher Wren applied these findings to createan early ventilation system for the Houses of Parliament, this system used bellows to circulate air, to stop it becoming stagnant and help with ventilation. Wren’s pioneering system also proved to be the catalyst for much later improvement and innovation. The first recorded use of a rotary ventilation fan used in Europe can be traced back to the 16th century when one was used in a mine, as illustration of which was done by the German scholar Georg Agricola (1494–1555), whose interest in the mining of metals is well documented.
In 1727 the British engineer John Theophilus Desaguliers demonstrated how to successfully use a fan system to draw out stagnant air from coal mines, and soon afterwards he used theses same principles to install ventilation apparatus in Parliament. During this time the growing importance of good ventilation in coal mines had been recognised as an essential way to help reduce the amount of casualties being lost to asphyxiation. The civil engineers John Smeaton and John Buddle also installed ventilation systems in the mines of Northern England,however, because of the use of reciprocating pumps, which were seen as unreliable at the time, their arrangement were not ideal as the machinery kept breaking down.
With the advent of the industrial revolution and the practical use of steam power, fans finally had the mechanical power required to allow proper use for ventilation. In 1837 William Fourness of England installed a steam-driven fan at Leeds. In 1849 the Scottish inventor and engineer William Brunton developed and installed a 6m radius steam driven fanin the GellyGaer Colliery of South Wales. So impressive was this design that one was exhibited at the Great Exhibition of 1851. Again in 1851 another Scotsman, this time a prominent doctor by the name of David Boswell Reid, installed several steam powered fans in the ceiling of St George’s Hospital in Liverpool where he was working at the time. The thinking behind this system was that the pressure produced by the fans would force the incoming air upward and through vents in the ceiling.Other notable improvements in the technology were made by James Nasmyth (yet another Scottish engineer), Frenchman Theophile Guibal and finally J. R. Waddle.
During the years 1882 and 1886 an American called Schuyler Wheeler developed the first electrically powered fan, which was then commercially marketed by the American based Crocker & Curtis electric motor company. Philip Diehl then developed the world’s first electric ceiling fan in 1882.Throughout this intense period of innovation, and prior to the widespread availability of cheap electricity, fans were powered by all manner of fuels. Alcohol, oil, or Parafin were commonly used to fuel fans in the years surrounding the turn of the 20th century. In 1909, the Japanese firm KDK pioneered mass-produced electric ceiling fans, this meant they were relatively easily available for domestic use and easy retro-fitting wherever they were desired. As mass production techniques were developed and refined over the years it meant that by the 1920s, different shapes and styles of fan could be made cheaply using steel, therefore bringing fan prices down even further and allowing even more homeowners to afford them. With the advent of the art deco movement the “swan fan”was designed during the 1930’s so that fans would appeal to even the most fashion conscious home owner and hopefully become a ‘must have’ item. By the time 1940s came around the large Indian company Crompton Greaves became the biggest manufacturer of electric ceiling fans in the world,with India, Asia and the Middle East accounting for the vast majority of sales. Then with the moulding techniques, variety of colour schemes and unrestricted shape possibilities offered by plastic thenby the 1950s, table and stand fans had become bright and eye catching statement pieces essential for the modern home.
Following the development of window and central air conditioning in the 1960s many companies abandoned fan production in the rush to sell the latest cooling technology, especially as it offered much higher margins. However during in the 1970s, people had cottoned became aware of the extra power required to run these early air conditioning systems as the cost of electricity rose so once again started looking to turn-of-the-century styled ceiling fans as an energy efficient, more decorative form of ventilation and cooling.
By the end of the 20th century William Fairbank and Walter K. Boyd had invented the high-volume low-speed (HVLS) ceiling fan, which used long fan blades to move relatively large amounts of air and thereby reduce the energy consumption required to run them compared to traditional ceiling fans.
Types of Fan
Mechanical fans are among the most ubiquitous items in the world, they come in a host of size’s, shapes, colours, and voltages to suit almost any application where airflow is required. They can be used on the floor, table, desk, or as we’ve discussed hung from the ceiling (ceiling fan). In ventilation type applications you’ll find them mounted in window’s, walls, roofs, and even chimneys etc. Even inside high tech electronic equipment such as computers and server racks you’ll quite often find a fan providing a stream of air to help keep the circuits inside cool. More obviously perhaps you’ll also find them in appliances such as hair dryers and portable industrial electric space heaters and mounted/installed wall heaters. They are also used for moving air in air-conditioning systems such as a portable air conditioner, and even car engines where they’re usually be driven by either fly wheels and belts or direct motors. Although fans are generally used for comfort by creating wind chill thereby increasing the heat transfer coefficient it is worth remembering they do not physically lower temperatures directly. When a fan is used to cool electrical equipment, engines or other machines they do cool the equipment directly by forcing hot air into the cooler environment outside of the machine.
There are three main types of fans used for moving air these are; axial, centrifugal (also known as radial) and cross flow (sometimes called tangential). The standard for assessing fan performance is included in the American Society of Mechanical Engineers Performance Testing Code 11 (PTC), which includes test methods and reporting on all fans, including centrifugal, axial, and mixed flows.
Axial Flow Fans
Axial-flow get their name from the fact they use their blades to move air across them, parallel to the shaft about around which the blades turn and perpendicular to the blades themselves. This type of fan is what most people picture when they think of a ‘fan’ which is probably because they’re used in such a wide variety of applications, ranging from the small cooling fans you find in computers and electronics all the way up to the giant ones used to create wind tunnels. Axial flow fans are also commonly used in portable air conditioning and industrial process applications. Standard axial flow fans have generally diameters ranging from about 200–400 mm to 1,800–2,000 mm and work against head pressures up to 800 Pa. Other special types of fan can be used as low pressure compressor stages in aircraft engines. Examples of axial fans are:
- Man cooler fan such Table fan: The basic elements of a typical table fan are the fan blade, base, armature and lead wires, motor, finger guard, motor housing, oscillator mechanism, and oscillator shaft. The oscillator is the thing that turns the fan from side to side. The armature axle shaft comes out on both ends of the motor, one end of the shaft is attached to the blade and the other is attached to the oscillator gearbox. The motor case joins to the gearbox to contain the rotor and stator. The oscillator shaft combines to the weighted base and the gearbox. A motor housing covers the oscillator mechanism. The blade guard joins to the motor case for safety.
- Domestic Extractor Fan: Wall or ceiling mounted, the domestic extractor fan is employed to remove moisture and stale air from domestic dwellings. Bathroom extractor fans typically utilize a four-inch (100 mm) impeller, whilst kitchen extractor fans typically use a six-inch (150 mm) impeller as the room itself is often bigger. Axial fans with five-inch (125 mm) impellers are also used in larger bathrooms though are much less common. Domestic axial extractor fans are not suitable for duct runs over 3 m or 4 m, depending on the number of bends in the run, as the increased air pressure in longer pipework inhibits the performance of the fan.
- Electro-mechanical fans such as warehouse fans: Among collectors, are rated according to their condition, size, age, and number of blades. Four-blade designs are the most common. Five-blade or six-blade designs are rare. The materials from which the components are made, such as brass, are important factors in fan desirability.
- Ceiling fan: A fan suspended from the ceiling of a room is a ceiling fan. Most ceiling fans rotate at relatively low speeds and do not have blade guards. Ceiling fans can be found in both residential and industrial/commercial settings.
- In automobiles, a mechanical fan provides engine cooling and prevents the engine from overheating by blowing or drawing air through a coolant-filled radiator. The fan may be driven with a belt and pulley off the engine’s crankshaft or an electric motor switched on or off by a thermostatic switch.
- Computer fan for cooling electrical components
- Fans inside audio power amplifiers help to draw heat away from the electrical components.
80 hp supply fan
- Variable-pitch fan: A variable-pitch fan is used where precise control of static pressure within supply ducts is required. The blades are arranged to rotate upon a control-pitch hub. The fan wheel will spin at a constant speed. The blades follow the control pitch hub. As the hub moves toward the rotor, the blades increase their angle of attack and an increase in flow results.
Also often called a “squirrel cage” (because of its general similarity in appearance to exercise wheels for pet hamsters) or “scroll fan”, centrifugal fans moving component (called an impeller) consists of a central shaft about which a set of blades that form a spiral, or ribs, are positioned. Centrifugal fans blow air at right angles to the intake of the fan, and spin the air outwards to the outlet (by deflection and centrifugal force). The impeller rotates, causing air to enter the fan near the shaft and move perpendicularly from the shaft to the opening in the scroll-shaped fan casing. A centrifugal fan produces more pressure for a given air volume, and is used where this is desirable such as in leaf blowers, blowdryers, air mattress inflators, inflatable structures, climate control equipment such as portable air con, large industrial electric fan heaters, and various other industrial purposes. They are typically noisier than comparable axial fans.
The cross-flow or tangential fan, sometimes known as a tubular fan, was patented in 1893 by Paul Mortier, and is used extensively in heating, ventilation, and air conditioning (HVAC). The fan is usually long in relation to the diameter, so the flow remains approximately two-dimensional away from the ends. The cross-flow fan uses an impeller with forward-curved blades, placed in a housing consisting of a rear wall and a vortex wall. Unlike radial machines, the main flow moves transversely across the impeller, passing the blading twice.
The flow within a cross-flow fan may be broken up into three distinct regions: a vortex region near the fan discharge, called an eccentric vortex, the through-flow region, and a paddling region directly opposite. Both the vortex and paddling regions are dissipative, and as a result, only a portion of the impeller imparts usable work on the flow. The cross-flow fan, or transverse fan, is thus a two-stage partial admission machine. The popularity of the crossflow fan in HVAC equipment comes from its compactness, shape, quiet operation, and ability to provide a high pressure coefficient. Effectively a rectangular fan in terms of inlet and outlet geometry, the diameter readily scales to fit the available space, and the length is adjustable to meet flow rate requirements for the particular application.
Common household tower fans are also cross-flow fans. Much of the early work focused on developing the cross-flow fan for both high- and low-flow-rate conditions, and resulted in numerous patents. Key contributions were made by Coester, Ilberg and Sadeh, Porter and Markland, and Eck. One interesting phenomenon particular to the cross-flow fan is that, as the blades rotate, the local air incidence angle changes. The result is that in certain positions the blades act as compressors (pressure increase), while at other azimuthal locations the blades act as turbines (pressure decrease).
Since the flow both enters and exits the impeller radially, the crossflow fan is well suited for aircraft applications. Due to the two-dimensional nature of the flow, the fan readily integrates into a wing for use in both thrust production and boundary-layer control. A configuration that utilizes a crossflow fan is located at the wing leading edge is the fanwing. This design creates lift by deflecting the wake downward due to the rotational direction of the fan, causing large Magnus force, similar to a spinning leading-edge cylinder. Another configuration utilizing a crossflow fan for thrust and flow control is the propulsive wing. In this design, the crossflow fan is placed near the trailing edge of a thick wing, and draws the air off the wing’s suction (top) surface. By doing this, the propulsive wing is nearly stall-free, even at extremely high angles of attack, producing very high lift. The external links section provides links to these concepts.
A cross flow fan, is a centrifugal fan in which the air flows through the fan, rather than through an inlet. The rotor of a cross flow fan is covered to create a pressure differential. Cross flow fans have a smaller opening on one side and a larger opening on the other. The resultant pressure difference allows air to flow straight through the fan, even though the fan blades counter the flow of air on one side of the rotation. Cross flow fans give airflow along the entire width of the fan; however, they are noisier than ordinary centrifugal fans, presumably[because the fan blades fight the flow of air on one side of the rotation unlike typical centrifugal fans. Cross flow fans are often used in portable air conditioners, commercial electric heaters and automobile ventilation systems, and for cooling in medium-sized equipment such as photocopiers.
Uncommon types of fan
Although not really used in climate control here are a few examples of some lesser used types for fan, just for the sake of completion, context and general knowledge.
Bellows are also used to move air, although not generally considered fans. A hand-operated bellows is essentially a bag with a nozzle and handles, which can be filled with air by one movement, and the air expelled by another. Typically it would comprise two rigid flat surfaces hinged at one end, where a nozzle is fitted, and with handles at the other.
The sides of the surfaces are joined by a flexible and air-proof material such as leather; the surfaces and joining material comprise a bag sealed everywhere but at the nozzle. (The joining material typically has a characteristic pleated construction that is so common that similar expanding fabric arrangements not used for moving air, such as on a folding camera, are called bellows.) Separating the handles expands the bag, which fills with air; squeezing them together expels the air. A simple valve (e.g., a flap) may be fitted so that air enters without having to come from the nozzle, which may be close to a fire.
Bellows produce a directed pressurized stream of air; the airflow volume is typically low with moderate pressure. They are an older technology, used mainly to produce a strong and directed airflow unlike non-electric bladed mechanical fans, before the introduction of electricity.
- A single-acting bellows will only produce airflow during the exhaust stroke.
- A double-acting bellows is a pair of bellows capable of blowing out air from one while inhaling air into the other, but airflow still temporarily ceases when the stroke direction is reversed.
- Combining multiple bellows at third-cycle or quarter-cycle arrangements on a crank arm allows for nearly continuous airflow from several bellows at once; each is in a different phase of inhaling and exhausting during the cycle.
The British engineer and inventor James Dyson developed Air Multiplier fans, and the Imperial C2000 series range hood fans, which famously have no visible fan blades or other moving parts except their oscillating and tilting head. The airflow is generated using the Coandă effect; a small quantity of air from a high-pressure-bladed impeller fan, contained in the base rather than exposed, drives a large air mass via a low-pressure area created by the airfoil. The US Patent & Trademark Office initially ruled that Dyson’s patent was not an improvement on the patent already held by Toshiba for their almost identical bladeless desktop fan granted in 1981. Air curtains and air doors also utilize this effect to help retain warm or cool air within an otherwise exposed area that lacks a cover or door. Air curtains are commonly used on open-face dairy, freezer, and vegetable displays to help retain chilled air within the cabinet using a laminar airflow circulated across the display opening. The airflow is typically generated by a mechanical fan of any type described in this article hidden in the base of the display cabinet.
Differences in air temperature will affect the density of air and can be used to induce air circulation through the mere act of heating or cooling an air mass. This effect is so subtle and works at such low air pressures that it does not appear to fit the definition of a fan technology. However, prior to the development of electricity, convective airflow was the primary method of inducing airflow in living spaces. Old fashioned oil and coal furnaces were not electric and operated simply on the principle of convection to move the warm air. Very large volume air ducts were sloped upwards away from the top of the furnace towards floor and wall registers above the furnace. Cool air was returned through similar large ducts leading to the bottom of the furnace. Older houses from before electrification often had open duct grilles leading from the ceiling of a lower level to the floor of an upper level, to allow convective airflow to slowly rise up the building from one floor to the next. Outhouses commonly rely on a simple enclosed air channel in a corner of the structure to exhaust offensive odors. Exposed to sunlight, the channel is warmed and a slow convective air current is vented out the top of the building, while fresh air enters the pit through the seat hole
An electrostatic fluid accelerator propels airflow by inducing motion in airborne charged particles. A high voltage electric field (commonly 25,000 to 50,000 volts) formed between exposed charged anode and cathode surfaces is capable of inducing airflow through a principle referred to as ionic wind. The airflow pressure is typically very low but the air volume can be large. However, a sufficiently high voltage potential can also cause the formation of ozone and nitrogen oxides, which are reactive and irritating to mucous membranes.
Fans generate noise from the rapid flow of air around blades and obstacles causing vortexes, and from the motor. Fan noise has been found to be roughly proportional to the fifth power of fan speed; halving speed reduces noise by about 15 dB.
Fan motor drive methods
Standalone fans are usually powered by an electric motors, often attached directly to the motor’s output, with no gears or belts. The motor is either hidden in the fan’s center hub or extends behind it. For big industrial fans, three-phase asynchronous motors are commonly used, placed near the fan and driving it through a belt and pulleys. Smaller fans are often powered by shaded pole AC motors, or brushed or brushless DC motors. AC-powered fans usually use mains voltage, while DC-powered fans use low voltage, typically 24V, 12V, or 5 V. Cooling fans for computer equipment always use brushless DC motors, which generate much less electromagnetic interference than other types.
In machines with a rotating part, the fan is often connected to it rather than being powered separately. This is commonly seen in motor vehicles with internal combustion engines, large cooling systems, locomotives, and winnowing machines, where the fan is connected to the drive shaft or through a belt and pulleys. Another common configuration is a dual-shaft motor, where one end of the shaft drives a mechanism, while the other has a fan mounted on it to cool the motor itself. Window air conditioners commonly use a dual-shaft fan to operate separate blowers for the interior and exterior parts of the device.
Where electrical power or rotating parts are not readily available, fans may be driven by other methods. High-pressure gases such as steam can be used to drive a small turbine, and high-pressure liquids can be used to drive a pelton wheel, either which can provide the rotational drive for a fan.
Large, slow-moving energy sources such as a flowing river can also power a fan using a water wheel and a series of step-down gears or pulleys to increase the rotational speed to that which is required for efficient fan operation.
Solar powered fan
Electric fans used for ventilation may be powered by solar panels instead of mains current. This is an attractive option because once the capital costs of the solar panel have been covered, the resulting electricity is free. In addition, electricity is always available when the sun is shining and the fan needs to run.
A typical example uses a detached 10-watt, 12 in × 12 in (30 cm × 30 cm) solar panel and is supplied with appropriate brackets, cables, and connectors. It can be used to ventilate up to 1,250 square feet (116 m2) of area and can move air at up to 800 cubic feet per minute (400 L/s). Because of the wide availability of 12 V brushless DC electric motors and the convenience of wiring such a low voltage, such fans usually operate on 12 volts.
The detached solar panel is typically installed in the spot which gets most of the sun light and then connected to the fan mounted as far as 25 feet (8 m) away. Other permanently-mounted and small portable fans include an integrated (non-detachable) solar panel.
Here at Broughton EAP Ltd we have been manufacturing portable industrial ventilation fans, cooling fans and extractor units for almost 40 years. We offer a range of portable solutions that can help you achieve better airflow and they are ideal for additional cooling during summer, extra ventilation when required or as portable extraction fans for use by tradespeople such as log burner fitters, welders or joiners. Should you require any further information on our fans, air con units, industrial electric space heaters, evaporative coolers, portable boilers or commercial dehumidifiers then please do not hesitate to contact us on 01527 830610 or firstname.lastname@example.org