This article discusses high-volume low-speed (HVLS) fans that keep industrial units cool. High ceilings, heat generating motors and furnaces, and poor ventilation often work together to keep industrial spaces hot. The idea behind the HVLS fan originated several years ago from a class project at the Cooperative Extension of the University of California at Riverside, which develops applications for the state’s agriculture industry. HVLS fans rotate slowly, at 25 to 125 rpm, powered by a motor of less than one horsepower. The concept behind the HVLS fan is to move large amounts of air slowly. The fan produces a soft, cooling breeze that is effective in mixing the air in the plant. A single 20-foot HVLS fan costs $3,750. With average operating costs as low as five to 10 cents an hour, depending on utility rates, HVLS fans offer a simple, low-cost approach to keeping big industrial spaces comfortable.
Hot, stifling working conditions take a toll on productivity. During peak summer months, it's not uncommon for temperatures to top 95°F in some plants. Unfortunately, keeping large spaces, such as factories and warehouses, at a comfortable temperature is often a challenge. High ceilings, heat generating motors and furnaces, and poor ventilation often work together to keep industrial spaces hot. Ventilation systems, which are primarily designed to supply clean, uncontaminated air, seldom generate enough circulation within a large workspace to provide a cool breeze. Air conditioning is frequently prohibitively expensive in these buildings.
Winter poses its own set of problems. Cold air enters from loading docks and can spread quickly through the building, creating cold .spots that are hard to dissipate. To give clearance to cranes and other equipment, heaters are often placed too high above floor level to be effective.
Beating the Heat
Prior to the summer of 1999, Agri-Fab Inc., a large manufacturer of lawn and garden equipment in Sullivan, Ill., responded to summer heat the way many industrial plants do: with lots of small, high-speed fans placed around work areas . The plant, which totaled about 100,000 square feet, consisted of a building that had been expanded over the years. Varying roof heights and shapes throughout the plant made it difficult to get consistent airflow in any direction.
As a particularly brutal heat wave swept across the prairie last summer, Agri-Fab's managers looked for a better way to cool the assembly area, an approximately 60,000-square-foot space occupied by more than 150 people. In July, temperatures in the assembly area sometimes exceeded 90°F. In an attempt to provide relief, the company previously installed two dozen 36-inch highspeed industrial fans, each mounted about 12 feet above the floor and tilted toward the assembly lines. Each fan produced a breeze within an 8- to 10-foot-wide tunnel that traveled about 30 to 40 feet. All 24 fans working together covered less than 10,000 square feet.
"This makeshift solution provided some relief, but the fans were noisy and didn't reach every worker either effectively or consistently:' said Tom Waskom, an industrial technology professor at Eastern Illinois University in Charles ton, who was called in as a consultant. Waskom eliminated an obvious alternative, air conditioning, as too expensive. In casting about for a better answer, he learned of high-volume low-speed fans, produced by the HVLS Fan Co. of Lexington, Ky.
Waskom ordered one 20-foot-diameter HVLS fan for the Agri-Fab plant in July. After a brief trial run, he ordered 10 more fans, seven with 20-foot diameters and three with 10-foot diameters, in time for one of the hottest months on record. The in-house maintenance crew was able to install the fans in a matter of hours. The fans were hung horizontally from the ceiling with 4x4- inch square tubing having 0.25-inch wall thickness. The fans were suspended about six feet below the ceiling, and approximately 28 feet above the floor.
The assembly area is divided in half by conveyors that feed parts to assembly and move finished goods to shipping. Each half contains six assembly lines. Eight 20-foot HVLS fans are positioned along two rows-one row for each side of the assembly area. Each fan covers an area of 10,000 to 15,000 square feet, and together the eight fans provide more than enough coverage for the assembly area, according to Waskom. The three 10-foot-diameter HVLS fans are installed in an adjacent area, over paint lines.
Although the HVLS fans were purchased during the summer, Waskom believes that they will provide comfort in the winter as well. Subzero temperatures are not uncommon in Illinois during the winter, and continual opening of the loading dock door's allows cold air to spread quickly throughout the building, creating pockets of cold air.
The Agri-Fab plant is heated by gas heaters placed about 20 feet above the floor. Much of the hot air from the heaters rises to the ceiling, where it is wasted. Stratification of temperatures can be costly to large plants in winter. The temperature difference between floor and ceiling can be as much as 15°F. This means that the ceiling would have to be heated to 85°F to maintain 70°F at floor level.
"The same lack of air circulation that creates problems in the summer is also a problem in the winter," Waskom said. "Basically, most of the heat rises up to the ceiling and stays there. We expect that considerable savings can be realized by moving that heat to the floor level. The HVLS fans will be able to create exactly the kind of air mixing that is needed in our situation. The way the fans are now situated, the warm air from the ceiling should easily neutralize any cold draft that works its way into the assembly area from shipping."
The idea behind the high-volume low-speed fan originated several years ago from a class project at the Cooperative Extension of the University of California at Riverside, which develops applications for the state's agriculture industry. An engineer at the school, William Fairbank, came up with the idea of a large ceiling fan as an economical way of cooling dairy herds, which stop producing milk when it gets too hot. Fairbank, who was then close to retirement, had his students build a large paddle fan, but did not pursue the project further. However, he did pass along his idea to Walter Boyd, now a partner in the HVLS Fan Co., who began to refine it.
Boyd came up with the idea of using an extruded aluminum blade in the shape of an airfoil. He said he chose aluminum as a construction material because of its low cost, adding that incremental efficiency gains, which might be possible with more exotic materials such as composites, would not outweigh the additional manufacturing costs.
So far, the company has supplied fans from 8 feet to 20 feet in diameter, and is experimenting with a 24-foot fan. Although it's theoretically possible to go to greater diameters, the 20-foot size is desirable for a number of reasons-not least, the possible obstructions in an industrial space. Although the ideal elevation for these fans is about 18 to 25 feet from the floor level, the fans are still quite effective when placed as high as 45 feet, Boyd said.
The airfoil shape is essentially a sail-plane wing, long and narrow, with a high aspect ratio. "A long, skinny wing is very efficient," said Boyd. It's also a hollow section, and so is relatively lightweight. The 20-foot fan, which contains 10 blades, weighs about 240 pounds. When operating, the blades provide about 100 pounds of lift.
HVLS fans rotate slowly, at 25 to 125 rpm, powered by a motor of less than one horsepower. "We decided on the speed range we wanted to run this airfoil shape with the most efficiency. T hen we wanted to maximize the performance by using as many blades as we could," said Boyd. The airfoil has an angle of attack- the degree it is tipped-of8 degrees, similar to that of a typical airplane wing.
The 20- foot HVLS fan operates at about 50 rpm at 60 Hz, producing a laminar flow of air over the blade, which helps to provide quiet, efficient operation. The 20-foot HVLS fan is turned by a 0.75-hp three-phase induction ac motor through a 35:1 gear ratio. The fan uses a cycloidal gear reducer that is very compact.
The concept behind the HVLS fan is to move large amounts of air slowly. The fan produces a soft, cooling breeze that is effective in mixing the air in the plant. Wind speeds are only about 3.1 or 3.2 mph, producing a breeze of about 250 to 280 feet per minute. The fan's approach is the opposite of small, high-speed fans that essentially bore holes in the air, but are ineffective at mixing cooling outside a narrow column of turbulent air in their path.
Boyd said he made some interesting discoveries when studying the airflow produced by the HVLS fan. Each 20-foot fan moves a wide cylindrical column of air, producing a horizontal floor jet that radiates outward when it reaches the ground to cover 10,000 to 15,000 square feet. This is one reason why it produces a lot of coverage.
The depth of the floor jet, or its height off the floor, is determined by the velocity of the air coming down and the diameter of the fan. The floor jet must be deep enough to immerse the people in its random breezes to provide effective cooling.
The company claims that the airflow can reduce the effective temperature at floor level by as much as 8°F. Vertically mounted 8- to 10-foot-diameter HVLS fans can be used to cool mezzanine areas, where long, narrow aisles make it difficult to distribute air.
The fans also make sense when combined with air conditioning, Boyd added. "You can do away with a lot of ducts, and just use the fans to mix. But also, you don't have to pull the temperature down nearly as far."
The thorough mixing of air that is produced by the HVLS fans is evident when they are first turned on. Although accumulated hot air is forced down initially, raising the temperature by a few degrees, it dissipates within 10 or 15 minutes in buildings with at least some ventilation, according to Boyd, who said he has measured the effects.
In winter, the fans can be set to rotate more slowly, around 25 rpm, to gently push down accumulated hot air to the floor level while trying to minimize ventilation. "You don't want a draft, but you want to keep forcing the air back down, with a constant pressure." The company claims that the HVLS fans can help reduce demands for heated air by as much as 20 percent.
The mixing of air also helps to remove smoke and fumes in a plant, said Boyd. Big exhaust fans in many industrial buildings tend to draw air along the walls of a building, without changing the air in the middle of the room, he said. The mixing of the air by the HVLS fans improves ventilation by helping more dirty air to be exhausted.
In some installations, the company took a different approach, installing a series of 10-foot-diameter HVLS fans in a row along the ceiling. The fans create a column of air that draws dirty air from below and directs it to an exhaust fan or a vent.
A single 20-foot HVLS fan costs $3,750. With average operating costs as low as five to 10 cents an hour, depending on utility rates, HVLS fans offer a simple, low-cost approach to keeping big industrial spaces comfortable.