Ceiling fan
Elements
Basic elements of most electrical mechanical fans include the fan blade, base, stator with armature and lead wires, blade guard, motor housing, oscillator gearbox, rotor, and oscillator shaft. The oscillator is a mechanism that motions the fan from side to side. The rotor goes inside a stator. Current comes through the lead wires and flows into the armature, which is a series of electromagnets. The rotor makes and breaks contacts turning on (or off) each of the electromagnets. These pull the rotor around. One end of the rotor 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.
Electro-mechanical 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
Mechanical devices
Mechanically, a fan can be any revolving vane or vanes used for producing currents of air, in winnowing grain, blowing a fire, or for ventilation. A fan can also be used for checking rapid motion by the resistance of the air; e.g., a fan blower or a fan wheel.
Mechanical revolving blade fans are put on the floor or a table, or hung from the ceiling, or are built into a window, wall, roof, chimney, etc., and also into instruments, e.g. a computer. They are also used to move air for cooling purposes, as in automotive engines and air-conditioning systems, and are driven by belts or by direct motor. Fans create a wind chill but do not lower temperatures directly.
Mechanical development
The first recorded mechanical fan was the punkah fan used in the Middle East in the 1500s. It had a canvas covered frame that was suspended from the ceiling. Servants, known as punkah wallahs , pulled a rope connected to the frame to move the fan back and forth.
The Industrial Revolution in the late 1800s introduced belt-driven fans powered by factory waterwheels. Attaching wooden or metal blades to shafts overhead that were used to drive the machinery, the first industrial fans were developed. When Thomas Edison and Nikola Tesla introduced electrical power in the late 1800s and early 1900s for the public, the personal electrical fan was introduced. Between 1882 and 1886, Dr. Schuyler Skaats Wheeler developed the two-bladed desk fan, a type of personal electric fan. It was commercially marketed by the American firm Crocker & Curtis. In 1882, Philip H. Diehl introduced the electric ceiling fan. Diehl is considered the father of the modern electric fan. In the late 1900s, electric fans were used only in commercial establishments or in well-to-do households. Heat-convection fans fueled by alcohol, oil, or kerosene were common around the turn of the 20th century.
In the 1920s, industrial advances allowed steel to be mass-produced in different shapes, bringing fan prices down and allowing more homeowners to afford them. In the 1930s, the first art deco fan was designed. Before this fan, called the Silver Swan, most household fans were fairly plain. In the 1950s, fans were manufactured in colors that were bright and eye catching. Central air-conditioning in the 1960s brought an end to the golden age of electric fan. In the 1970s, Victorian-style ceiling fans became popular.
In the twentieth century, fans have become utilitarian. During the 2000s, fan aesthetics have become a concern to fan buyers. The fan is part of everyday life in the Far East, Japan, and Spain (among other places).
European fan
Asian fan
In China, screen fans were used throughout society. The earliest known Chinese fans are a pair of woven bamboo side-mounted fans from the 2nd century BC. The Chinese character for "fan" (扇) is etymologically derived from a picture of feathers under a roof. The Chinese fixed fan, pien-mien, means 'to agitate the air'.
Fans were part of the social status for the Chinese people. A particular status and gender would accord a specific type of fan to an individual. The folding fan was invented in Japan and taken to China in the 9th century. The Akomeogi (or Japanese folding fan; 衵扇; Hiôgi) originated in the 6th century. These were fans held by aristocrats of the Heian period when formally dressed. They were made by tying thin stripes of hinoki (or Japanese cypress) together with thread. The number of strips of wood differed according to the person's rank. They are used today by Shinto priests in formal costume and are brightly painted. The Chinese dancing fan was developed in the 7th century. The Chinese form of the hand fan was a row of feathers mounted in the end of a handle.
In China, the folding fan came into fashion during the Ming dynasty between the years of 1368 and 1644, and Hangzhou was a center of folding fan production. The Mai Ogi (or Chinese dancing fan) has ten sticks and a thick paper mount showing the family crest. Chinese painters crafted many fan decoration designs. The slats, of ivory, bone, mica, mother of pearl, or tortoise shell, were carved and covered with paper or fabric. Folding fans have "montures" which are the sticks and guards. The leaves are usually painted by craftsman. Social significance was attached to the fan in the Far East. The management of the fan became a highly regarded feminine art. The function and employment of the fan reached its high point of social significance (fans were even used as a weapon - called the iron fan , or tieshan in Chinese, tessen in Japanese).
Printed fan leaves and painted fans are done on a paper ground. The paper was originally hand made and displayed the characteristic watermarks. Machine made paper fans, introduced in the 19th century, are smoother with an even texture.
Folding fans (扇子 Japanese "sensu", Chinese: "shanzi";) continue to be important cultural symbols and popular tourist souvenirs in East Asia.
Household Electric Fan
A fan has two purposes – to move air for human comfort or for ventilation and to move air or gas from one location to another for industrial purposes. Fans have broad surfaces that usually revolve. Leaves or flat objects, waved to produce a more comfortable atmosphere, are the simplest kind of fan.
Applications include ornamental decorations, climate control, cooling system, refreshing air, personal wind-generation (e.g., an electric table fan), ventilation (e.g., an exhaust fan), winnowing (e.g., separating chaff of grain), removing dust (e.g., sucking as in a vacuum cleaner), drying (usually in addition to heat) and to provide draft for a fire.
Types of fans
Mechanical revolving blade fans are made in a wide range of designs. In a home you can find fans that can be put on the floor or a table, or hung from the ceiling, or are built into a window, wall, roof, chimney, etc. They can be found in electronic systems such as computers where they cool the circuits inside, and in appliances such as hair dryers and space heaters. They are also used for moving air in air-conditioning systems, and in automotive engines, where they are driven by belts or by direct motor. Fans create a wind chill, but do not lower temperatures directly.
There are three main types of fans used for moving air, axial, centrifugal (also called radial) and crossflow (also called tangential).
Axial fans
The axial-flow fans have blades that force air to move parallel to the shaft about which the blades rotate. Axial fans blow air along the axis of the fan, linearly, hence their name. This type of fan is used in a wide variety of applications, ranging from small cooling fans for electronics to the giant fans used in wind tunnels.
Examples of axial fans are:
- Table fan: Basic elements of a typical table fan include the fan blade, base, armature and lead wires, motor, blade guard, motor housing, oscillator gearbox, and oscillator shaft. The oscillator is a mechanism that moves the fan from side to side. The axle comes out on both ends of the motor, one end of the axle 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.
- Ceiling fan: A fan suspended from the ceiling of a room is a ceiling fan.
- In automobiles, a mechanical fan provides engine cooling and prevents the engine from overheating by blowing or sucking air through a coolant-filled radiator. It can be driven with a belt and pulley off the engine's crankshaft or an electric fan switched on or off by a thermostatic switch.
- Computer cooling 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. As the hub moves toward the rotor, the blades increase their angle of attack and an increase in flow results.
Centrifugal fan
Often called a "squirrel cage" (because of its similarity in appearance to exercise wheels for pet rodents), the centrifugal fan has a moving component (called an impeller) that consists of a central shaft about which a set of blades, 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, and various industrial purposes. They are typically noisier than comparable axial fans.
Crossflow fan
The crossflow or tangential fan, sometimes known as a tubular fan was patented in 1893 by Mortier, and is used extensively in the HVAC industry. The fan is usually long in relation to the diameter, so the flow approximately remains two-dimensional away from the ends. The CFF uses an impeller with forward curved blades, placed in a housing consisting of a rear wall and vortex wall. Unlike radial machines, the main flow moves transversely across the impeller, passing the blading twice.
The flow within a crossflow 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 crossflow fan, or transverse fan, is thus a two-stage partial admission machine. The popularity of the crossflow fan in the HVAC industry comes from its compactness, shape, quiet operation, and ability to provide 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.
Much of the early work focused on developing the crossflow 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 crossflow 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).
Types
There are two types of fan:
- Ceiling Mounted: Mounted on ceiling between the attic and living space.
- Ducted: Remotely mounted away from the ceiling; can exhaust heat from multiple locations; operation is extremely quiet
Drawbacks
Air is drawn into the house through open windows, meaning that the air is unfiltered and may contain pollen or other allergens. This is in contrast to an air conditioner, which mainly circulates air through a heat exchanger.
The fan can also be noisy. The noise is due to the large volume of air handled by such a fan and the speed of the fan blades. Direct drive motors spin the blades faster, producing more noise compared to belt-driven fans, which allow lower fan speeds and less noise. The noise may interfere with other normal household activities such as listening to music, watching television, or conversation
Benefits whole-house fan
whole-house fan can significantly lower the temperature in a building very quickly, and is much less expensive to operate than air conditioning. Newer whole house fans can be environmentally friendly and energy efficient additions to house cooling systems. On temperate days they can be turned on to circulate rising hot air out of the house while pulling cool air in. Also new models are quieter and smaller than their older counterparts.
Whole-house fan From Wikipedia, the free encyclopedia
A whole-house fan is a type of fan installed in a building's ceiling, designed to pull hot air out of the building. It is sometimes confused with an attic fan.
A whole-house fan pulls hot air out of a building and forces it into the attic space. This causes a positive pressure in the attic forcing air out through the gable and/or soffit vents, while at the same time producing a negative pressure inside the living areas which draws cool air in through open windows.
Attic fans, by comparison, only serve to remove some hot air from the attic; no direct cooling effect is provided to the actual living space.
Crossflow fan
The crossflow or tangential fan, sometimes known as a tubular fan was patented in 1893 by Mortier, and is used extensively in the HVAC industry. The fan is usually long in relation to the diameter, so the flow approximately remains two-dimensional away from the ends. The CFF uses an impeller with forward curved blades, placed in a housing consisting of a rear wall and vortex wall. Unlike radial machines, the main flow moves transversely across the impeller, passing the blading twice.
The flow within a crossflow 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 crossflow fan, or transverse fan, is thus a two-stage partial admission machine. The popularity of the crossflow fan in the HVAC industry comes from its compactness, shape, quiet operation, and ability to provide 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.
Much of the early work focused on developing the crossflow 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 crossflow 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).
MULTIMEDIA
the Modern Fan Company in Ashland, Ore., had never owned a fan when he was hired by a ceiling fan company to create a contemporary-looking one in the mid-1980s, he said.
“At that point, ceiling fans had never really been a design object,” said Mr. Rezek, who had spent the previous 15 years designing lighting. “Most of the fans on the market were reproduction Victorian fans, and if a guy had a Mies van der Rohe apartment in Chicago, he probably wasn’t going to put one in there.”
After researching the mechanics of fans and developing a system that allowed the blade to attach directly to the rotor instead of an intermediary arm, he created the Stratos, a sleek model with four brushed aluminum blades. It quickly became popular in both commercial and residential settings.
Portable fans, Mr. Rezek noted, could use a little design help as well.
Fan motor
A standalone fan is typically powered with an electric motor. Fans are often attached directly to the motor's output, with no need for gears or belts. The electric 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 24 V, 12 V or 5 V. Cooling fans for computer equipment exclusively use brushless DC motors, which produce much less electromagnetic interference.
In machines that already have a motor, the fan is often connected to this rather than being powered independently. This is commonly seen in cars, boats, locomotives and winnowing machines, where the fan is connected either directly 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.
See also
History
The Industrial Revolution in the late 19th century introduced belt-driven fans powered by factory water wheels. Attaching wooden or metal blades to shafts overhead that were used to drive the machinery, the first industrial fans were developed. One of the first workable mechanical fans was built by Omar-Rajeen Jumala in 1832. He called his invention, a kind of a centrifugal fan, an "air pump." Centrifugal fans were successfully tested inside coal mines and factories in 1832–1834. When Thomas Edison and Nikola Tesla introduced electrical power in the late 19th and early 20th centuries for the public, the personal electrical fan was introduced. Between 1882 and 1886, the American engineer Schuyler Skaats Wheeler developed the two-bladed desk fan, a type of personal electric fan. It was commercially marketed by the American firm Crocker & Curtis electric motor company. In 1882, Philip Diehl introduced the electric ceiling fan. Diehl is considered the father of the modern electric fan. In the late 19th century, electric fans were used only in commercial establishments or in well-to-do households. Heat-convection fans fueled by alcohol, oil, or kerosene were common around the turn of the 20th century.
[FIGURE 4 OMITTED]
EVALUATION OF THE CFE INDEX OF COOLING FANS
COOLING-FAN EFFICIENCY INDEX
The body cooling effect produced by a fan depends on generated air velocity and turbulence field, body area exposed to moving air, body posture, air and mean radiant temperature, air humidity, clothing insulation, metabolic rate, humidity, and skin wettedness. Sophisticated thermal manikins with full body size and a complex shape were developed and used to determine the dry-heat loss from the human body under different environmental conditions (Tanabe et al. 1994; Tsuzuki et al. 1999; Melikov et al. 2002). A manikin's body is typically divided into several segments. They can be operated to maintain constant heat flux from the body, constant body surface temperature, or to have surface temperature equal to the skin temperature of an average person in a state of thermal comfort under the particular environmental condition of the exposure. Thermal manikins can be used to measure the fan cooling effect and, thus, to determine the CFE index. Thermal manikins that can measure dry-heat loss from the human body are commonly used today, though sweating thermal manikins are under development as well (Psikuta et al. 2008). Therefore, at this stage, dry-heat loss from the human body can be used to determine the CFE. In the future, more precise or effective ways of measuring the cooling effect may be developed and used instead of thermal manikins. Clothing thermal insulation and metabolic rate (personal factors that may vary substantially in real life) can be assumed to be constant, while air humidity and skin wettedness are not taken into account. The equivalent temperature ([t.sub.eq]) is a well-known parameter that can be used to determine the CFE index. The equivalent temperature (formerly equivalent homogenous temperature) is defined as "The uniform temperature of the imaginary enclosure with air velocity equal to zero in which a person will exchange the same dry heat by radiation and convection as in the actual nonuniform environment" (SAE 1993; ISO 2004). In the definition, it is assumed that the body posture, the activity level, and the clothing design and thermal insulation are the same in both environments. The equivalent temperature is a pure physical quantity that integrates the independent effects of convection and radiation on human body heat loss in a physically sound way. The equivalent temperature [t.sub.eq] does not take into account human perception and sensation or other subjective aspects, but may correlate with them. It is important to notice that [t.sub.eq] is not a temperature that can be measured by a thermometer and that [t.sub.eq] cannot be translated to an air temperature in a complex climate (Bohm et al. 1999). The body cooling effect achieved by air movement can be quantified by the change in whole-body manikin-based equivalent temperature [t.sub.eq] from the reference condition [t.sub.eq] * (similar indoor environmental conditions but without air movement) (i.e., [DELTA][t.sub.eq] = [t.sub.eq] - [t.sub.eq] *s). The concept of [DELTA][t.sub.eq] already has been used by several authors to quantify the whole-body cooling effect of air movement (Tanabe et al. 1994; Tsuzuki et al. 1999; Melikov et al. 2002; Watanabe et al. 2005; Sun et al. 2007). Thus, the CFE is defined by Equation 1.
