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6 BLADES VERSUS 10 BLADES Advances in HVLS Technology
6 BLADES VERSUS 10 BLADES Advances in HVLS Technology
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Energy is Expensive Energy is expensive, especially when it comes to heating and cooling. Whatever part of the country you do business in, you’re most likely looking for ways to lower your energy costs. In addition, businesses are now encouraged by federal, state, and even supply chain partners and customers, to lower carbon footprints and develop and implement “green” practices and products. Understanding these pressures, in 2005 MacroAir set out to meet this need by making its high volume low speed (HVLS) commercial ceiling fans more efficient. The company researched the possibility of changing the airfoil shape of the fan blades. With changing extrusion capacities, the ability to extrude a larger shape could be discussed, as well as creating a new, larger blade shape that would function efficiently through a wide range of speeds. What really intrigued MacroAir engineers was the idea of reducing the number of fan blades without affecting performance. HVLS technology originator and MacroAir company founder, Walter Boyd, developed the original 10-blade HVLS fan in 1995. This 10-blade design was extraordinary at the time, as nothing like it existed; since then, thousands of agricultural, manufacturing, and commercial enterprises across the U.S. have installed HVLS fans in order to reduce energy costs and improve heating and cooling. Thus, the objectives became:
• Create a larger airfoil shape • Reduce the number of blades to make the fan lighter and more efficient • Lower MacroAir’s carbon footprint
After months of research, design, experimentation, and testing, the result was a completely new six-blade HVLS fan; one that was lighter, more efficient, and better performing. With the new generation of HVLS fan technology at hand, MacroAir proved that six-blade HVLS fans improve energy efficiency, lower costs, and reduce the carbon footprint in the manufacturing process and for its customers. History of HVLS Fans An inventor his entire life, MacroAir founder Walter Boyd was challenged to help create an efficient system to cool dairy cattle. The issue involved milk production from dairy cattle as when they suffer from heat stress, they stop eating. When the cows don’t eat, milk production slows or comes to a halt – a bottom-line breaking
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challenge for dairy farmers in an already highly competitive business. At the time, small high-speed box fans helped, but didn’t cover a wide enough area and were considerably less efficient, consumed excessive and costly energy, and required ongoing maintenance. Typically, these fans also have a short mechanical life. Taking advantage of the laws of physics, Boyd designed a large, slow moving overhead fan that moved a large volume of air gently down to the ground and outward 360 degrees. This large, slow moving air mass moved throughout the barn, continuously mixing incoming fresh air with stale air, and minimized the amount of ventilation required to achieve good air quality. Most importantly, the new fans cooled the cows and increased milk production without causing them stress due to excessive noise or kick-up of dust. The HVLS barn fan models (AirVolution™ and MaxAir™) used 10 airfoil blades that incorporated design characteristics developed at NASA. How HVLS Fans Work You don’t need a physics degree to know that a breeze moving across your skin on a hot day feels good, especially in humid environments. The cool moving air breaks up the moisture-saturated boundary layer surrounding the body, accelerating evaporation to produce a cooling effect. People have been using fans to cool themselves long before the advent of the electric motor. At some point however, engineers became so focused on using speed to increase fan displacement – the cubic feet of air per minute (CFM) moved through a fan –that some important physics-based issues were overlooked. While having a cool breeze brush over your hot skin feels good, high velocity air movement is both unpleasant and disruptive. Additionally, air speed beyond four or five miles per hour usually offers little, if any, additional cooling benefit, as very slow moving air actually cools best in very hot, highly humid conditions. Small high-speed box fans create a pressure differential that’s essential for many applications; however where gentle movement of air is the objective, pressure differential is not important. Therefore, displacement, the amount of air that actually moves through the fan, is of no real significance. It’s the down-stream effects that are important. A turbulent, high-velocity air jet dissipates very quickly. A large column of air, however, “travels” farther than a small one. The friction between moving air and stationary air occurs at the periphery of the moving column. The perimeter of a column varies directly with column diameter. While the cross-sectional area varies with the square of the diameter, the large column has proportionately fewer
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peripheries, and therefore less “drag.” The air column from a three-foot diameter fan has more than six times as much “friction interface” per cubic foot as does the air column from a 20-foot fan. This is why a large, slow moving fan actually cools better and more efficiently than a small high-speed fan. 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. 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. Airspeed, combined with fan effectiveness, means that when the objective is to cool people or animals, very large, low-speed commercial fans are enormously more efficient and effective than small high-speed fans. Boyd’s new HVLS fan proved to be incredibly energy efficient. After much testing, he learned that one HVLS fan consumed about the same amount of electricity as one high-speed fan, while moving over 12 times the amount of air. New Advancements The Wickerbill™ Design A constant “tinkerer,” Boyd created an enhancement to increase the performance of his original airfoil blade design: the Wickerbill design. True to his racing car roots, he patterned the Wickerbill after the spoiler found on performance vehicles. Originally known as the Gurney Flap (named after Dan Gurney, the American race car driver and builder), the Wickerbill design added “down wash” to the airfoil blades, in the same manner a spoiler keeps the rear wheels of a car on the road. The Wickerbill resulted in almost a 30 percent increase in airflow CFM (cubic feet per minute) output with only a minimal increase in power consumption. The Wickerbill enhancement was particularly ideal for dairy and barn applications, where cooling and maximum air movement is desirable. Six Blades versus 10 Blades Extrusion is the name for the process used to manufacture objects of a fixed cross-sectional profile, including airfoil blades, plastic pipe, tubing and sheets of film, terra
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cotta bricks, and even food products. The material, such as plastic or metal, is heated and pushed through a die to form a specific shape. To create an HVLS fan blade, aluminum is heated, pushed through a die to create the foil, and then cut at the desired length. The larger the shape to be extruded, the more tonnage and capacity is required by the extruder. As extrusion capacities increased, MacroAir engineers began experimenting with larger airfoil shapes, something they couldn’t do when the first HVLS fans were created. Creating a larger airfoil wasn’t simply the answer to improving efficiency, though. The airfoil must work efficiently through a range of speeds. MacroAir engineers took into account that as an HVLS fan rotates, the end of the blade moves faster than it does at its fixed point at the fan hub. In addition, airflow patterns needed strong research and consideration. As company engineers experimented with airfoil shape, they discovered that a larger shape allowed them to reduce the number of blades. Final fan design saw a 40 percent reduction in blades, from 10 to six, without a corresponding drop in fan performance. Research proved beneficial as reducing the number of blades produced another benefit: reduced torque (the tendency of a force to rotate an object about an axis, fulcrum, or pivot). Fan longevity is related to torque: Horsepower = Torque * Revolutions Per Minute (RPM) 5252 As RPM goes up, torque goes down for the same horsepower. MacroAir engineers found that, due to the longer airfoil shape, six-blade HVLS fans rotated slightly faster than 10-blade fans, which lowered torque. Since torque is a constant stress on a fan’s motor, bearings, and gear, less torque meant longer fan life. Lower Carbon Footprint Although the new, larger fan blades required more material, the new six-blade fan design required fewer blades, translating into numerous unexpected benefits:
• 30 percent reduction in overall fan weight • Less stress on a building’s infrastructure • Reduced shipping costs • Lower energy costs
The new six-blade fan innovation also decreased the manufacturing carbon footprint.
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The electrolysis process used to produce aluminum requires large quantities of electrical power. When the cost of producing one ton of primary aluminum is broken down, almost one third is devoted to electrical power. The amount of electrical power needed to produce the new six-bladed HVLS fans was 13 percent lower than that of the 10-blade units, making the new fans very “green.” Improved fan performance Fan speed performance is measured using CFM (cubic feet per minute), or the measurement of volume over time; the higher a fan’s CFM number, the higher the volume or capacity of the fan. To measure the performance of an HVLS fan, MacroAir engineers used the method approved by the Air Movement and Control Association (AMCA) and measured “thrust,” which is the force the fan produces as a result of the air being pushed through it. The higher the thrust value, the higher the volume of air and fan performance or CFM, as seen in the table below: FAN SIZE SIX-BLADE HVLS FAN 10-BLADE HVLS FAN 8 FT 53,623 CFM1 39,000 CFM2 10 FT 83,0252 CFM2 74,122 CFM3 12 FT 97,695 CFM2 91,2853
1 AMCA Certified CFM 2 Derived from Certified Thrust Data for Comparison 3 CFM data not AMCA certified; data derived from internal calculations
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Improved Energy Efficiency In addition to requiring less energy during the manufacturing process, six-blade HVLS fans also require less energy to operate, as seen in the table below:
24” SIX-BLADE HVLS FAN
24” 10-BLADE HVLS FAN
CFM 376,664 303,613 AIRFOIL WEIGHT 103 LBS 146 LBS TORQUE 117 FT-LBS 162 FT-LBS SERVICE FACTOR ON GEARBOX
2.0
1.6
About MacroAir Since developing the first HVLS prototype in 1998, MacroAir continues to serve as an HVLS industry leader through its commitment to innovation and design of the most durable and cost-effective commercial ceiling fans on the market. As the “engineers of air™,” MacroAir produces energy-efficient, long-lasting HVLS fans that can be found in warehouses, manufacturing plants, airplane hangars, agricultural arenas and retail establishments across the U.S. and around the world, and are used by companies such as Coca-Cola, CSX Transportation and NAPA Auto Parts. The company is the exclusive HVLS fan supplier for independent auto dealerships of BMW, Chrysler, Ford, General Motors, Lexus, Mercedes-Benz, Nissan and Toyota under their Dealer Equipment Programs. Mailing Address 794 South Allen Street San Bernardino, CA 92408 Follow Us macroairfans.com Twitter: @MacroAirFans Facebook: facebook.com/MacroAir
