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A High-volume low-speed fanA high-volume low-speed (HVLS) fan is a type of mechanical fan greater than 7 feet (2.1 m) in diameter.[1] HVLS fans are generally ceiling fans although some are pole mounted. HVLS fans move slowly and distribute large amounts of air at low rotational speed&#; hence the name "high volume, low speed."
Typical applications for HVLS fans fall into two classifications&#;industrial and commercial. In industrial applications, HVACR is often cost prohibitive or impractical, and is usually only used for refrigerated warehouses or the manufacture of refrigerated or frozen foods.[2] Fans installed in spaces like warehouses, barns, hangars and distribution centers can prevent heat stress, increase worker comfort and the productivity of both workers and livestock.[3] HVLS fans are also used in commercial spaces, where air conditioning is more common, but increased air movement from ceiling fans can cost-effectively augment occupant comfort or prevent stratification. Typical commercial applications include shopping malls, churches, office buildings, airport terminal buildings, fitness centers and schools.
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In the late s, William Fairbank, a professor at the University of California at Riverside, and Walter K. Boyd, founder of MacroAir Technologies, invented and patented a new type of circulator fan, first called a High-Volume, Large-Diameter (HVLD) fan.[4] This type of fan was originally developed for agricultural applications, so early research focused on the benefits of HVLS fans on dairy production.[5][6][7]
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HVLS fans work on the principle that cool moving air breaks up the moisture-saturated boundary layer surrounding the body and accelerates evaporation to produce a cooling effect. Ceiling fans produce a column of air as they turn. This column of air moves down and out along the floor. Called a horizontal floor jet, this deep wall of horizontal moving air is relative to the diameter of a fan, and to a lesser degree, the speed of a fan. Once the floor jet reaches its potential, it migrates outward until it meets a side wall or other vertical surface.[8]
Under ideal conditions, an 8-foot-diameter (2.4 m) fan produces a floor jet of air approximately 36 inches (910 mm) deep. A 24-foot-diameter (7.3 m) fan produces a floor jet 108 inches (2,700 mm) deep, tall enough to engulf a human standing on the floor or a cow, its initial development purpose.[8]
Commercial HVLS fans differ from residential ceiling fans with regard to diameter, rotational speed, and performance. While some fans use contemporary blades to move air, other methods are being used to make it more efficient such as using airfoils.[citation needed]
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Larger diameter fans can move more air than smaller fans at the same speed. A turbulent, high velocity air jet dissipates very quickly. A large column of air, however, "travels" farther than a small one due to the friction between moving air and stationary air, which occurs at the periphery of the moving column.[8]
The perimeter of an air column varies directly with column diameter. While the cross-sectional area varies with the square of the diameter, the large column has proportionately fewer peripheries, and therefore less drag. The air column from a 3-foot-diameter (0.91 m) fan, therefore, has more than six times as much friction interface per volume of air moved as does the air column from a 20-foot-diameter (6.1 m) fan.[8]
When the down column of air from an HVLS fan reaches the floor, the air turns in the horizontal direction away from the column in all directions. The air flowing outward is called the "horizontal floor jet." Since the height of the floor jet is determined by the diameter of the column of air, a larger diameter fan naturally produces a larger air column and thus a higher floor jet.[8]
Smaller high-speed fans of equivalent displacement are incapable of producing the same effect.
The power to drive a fan increases roughly with the cube of the average air speed through the fan. A commercial fan delivering air at 20 miles per hour (mph) requires about 64 times as much power as a similar sized fan delivering air at five mph.[8]
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Airspeed, combined with fan "effectiveness," means that when the objective is to cool people or animals, very large, low-speed commercial fans are more efficient and effective than small high-speed fans.
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In general, Air Movement and Control Association Standard 230 sets uniform testing procedures for determining ceiling fan performance.
AMCA 230 establishes uniform methods of laboratory testing for air circulating fans in order to determine performance in terms of thrust for rating, certification or guarantee purposes. The version described a method to determine the thrust developed and used a simple equation to convert the measured thrust to airflow. During the periodic review process, it was determined that the calculated airflow was too high; therefore this version no longer artificially calculates airflow, but leaves the measured performance in units of thrust.
The current version, AMCA 230&#;12, reintroduced airflow rate with a revised equation, and new efficiency metrics. The official scope of the standard was limited to ceiling fans under 6 feet (1.8 m) in diameter.[9] Therefore, the current standard does not apply to HVLS fans. A new version of the standard is currently under review.
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Air movement can have a significant influence on human thermal comfort. Wind chill in cold conditions is considered detrimental, but air movement in neutral to warm environments is considered beneficial. This is because normally under conditions with air temperatures above about 74 °F (23.3°C), the body needs to lose heat in order to maintain a constant internal temperature.
Unlike air conditioners, which cool rooms, fans cool people. Ceiling fans increase air speed at the occupant level, which facilitates more efficient heat rejection, cooling the occupant, rather than the space.[10][11][12] Elevated air speed increases the rate of convective and evaporative heat loss from the body, thus making the occupant feel cooler without changing the dry bulb temperature of the air.
Hot air is less dense than cold air, which causes hot air to naturally rise to the ceiling level through a process called convection. In still air, layers of constant temperature form, the coldest at the bottom and the warmest at the top. This is called stratification. The most efficient and effective way of mixing the air in a stratified space is to push the hot air down to the occupant level. This allows for complete mixing of the air in the space while decreasing both heat loss through the building walls and roof, and building energy consumption. To avoid causing a draft, fans need to be run slowly so that air speed at the occupant level does not exceed 40 feet per minute (12 m/min).[13][14]
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MACROAIR HVLS Fans
The founder of Macroair Technologies Inc. is Mr. Walter Boyd who is the inventor of HVLS fans. Industry has gained many products such as motocross racing frames, aluminum felt layer for roofing, self-erecting portable video screen systems and of course HVLS fans through his investigative approach to various problems as an inventor.
In Mr. Boyd encountered a problem at a dairy farm run by his friend. The problem was; dairy cattle stop eating when they suffer from heat stress. When they don&#;t eat, milk production slows or comes to a halt. And the dairyman&#;s business becomes even more challenging. Small high-speed fans helped, but didn&#;t cover a wide enough area, are less efficient, consume excessive and costly energy, and require ongoing maintenance. Mr. Boyd designed a large, slow moving overhead barn fan that takes the advantage of the laws of physics. According to fan laws, a fan of 1/2 diameter would produce 1/8 the output; it would have to turn 8 times faster to match the output. Similar fan law states that; the power to drive a fan increases roughly with the cube of the average air speed through the air circulating fan, meaning if you increase the air velocity delivered by a fan-say 4 times-then you have to use 64 times more power! After being used in dairy barns, HVLS fans found themselves installation places at equine and poultry facilities, depots, warehouses, factories, sports arenas, hangars etc.
HVLS (High Volume Low Speed) fans move very slowly but (due to their big diameters) are capable to move high volume of air. With the advantage of slow moving they require very small amount of power compared to box fans. Low air velocity not only prevents the dust to be kept down but also increases the indoor air quality and the thermal comfort of living beings by gently evaporating the moisture on their skins (evaporative cooling). These fans support heating and cooling systems of the building and thus let the building owner reduce the energy need and its related costs. Frequency inverter and double direction (clockwise and reverse) features enable to set the thermostat upto 5 Deg C higher during the summer and 2-3 Deg C lower during winter without compromising thermal comfort. This ability lets heating and cooling appliances run less and save more from energy costs. Saving energy and its related costs help to achieve LEED points. MacroVoltaic, an innovative HVLS fan is the world&#;s first and only fan that can run 100% by solar power.
You may attain more information about Macroair Technologies Inc. and HVLS fans in the Literature section.
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