Large, Low Velocity Fans: Making Energy Efficiency a Breeze  

With rising energy costs and the increased accountability to operate efficiently, business owners, facility managers, home owners and architects are all looking for innovative ways to cut energy costs without cutting corners. And let's face it: not everyone can afford air conditioning or tolerates its negative environmental impact. One energy-conscious cooling alternative harkens back to the pre-air conditioning days — the ceiling fan. But this is not your grandmother's version; the traditional ceiling fan has been reinvented for large industrial, commercial, and residential spaces. The latest technology in industrial-grade air movement has been custom-engineered for shopping malls, offices, churches, schools and other sound-sensitive environments. Moreover, it has been executed on a scale large enough to make it a significant component of a cost-effective, energy-efficient building design.

Today's large, low velocity ceiling fans make the statement that it’s possible to create a beautiful environment utilizing serious energy-saving products. With Big Ass Fans, architects have the opportunity to implement sustainable products that are not just eco-friendly but also cost effective. This article will discuss the characteristics of large, low velocity ceiling fans, as well as their sustainability quotient, with an eye toward detailing energy costs. Practical considerations of specifying large, low velocity fans in large spaces will also be covered.

What is a large, low velocity ceiling fan?

Large, low velocity ceiling fans, also known as high volume, low speed (HVLS) fans, operate on a different principle than their conventional ceiling fan counterpart. These fans are significantly larger and operate at slow speeds to minimize power usage. The fans use aerodynamic, extruded aluminum airfoils designed to provide the optimum airflow at the lowest possible operating cost. These fans may have as many as ten blades that slowly revolve to create a massive, gentle current of air in all directions, covering up to 30,000 square feet of space. Because they move vast volumes of air, the fans can create a cooling effect over large areas. As a general rule of thumb, the more airfoils a fan has the more uniform the resulting airflow will be. Fewer blades will produce choppier bursts of air that dissipate more quickly, while fans with more blades establish a consistent circulation of air without needing to turn faster.

Large, low velocity fans are an aesthetic, energy-efficient way to keep large spaces comfortable. Photo Courtesy of Big Ass Fans®

These large fans operate with variable speed drives (VSD), allowing operation at higher speeds in summer and at lower speeds in winter. They typically have small motors ranging in size from 1/3 horsepower to 2 horsepower, and are used for cooling, heat recirculation, air distribution and as alternatives to air conditioning in large facilities. They are vastly more effective than high-speed fans, moving up to 36 times as much air. Also, due to their low operating speed, large, low velocity fans are very quiet.

Airflow Concept

Large, low velocity fans use their immense size – not speed – and aerodynamic airfoil and winglet design to move large volumes of air. Photo courtesy of Big Ass Fan Company®

Large, low velocity fans were invented more than a decade ago for large industrial and agricultural settings as an alternative to multiple conventional high speed fans, those large, caged fans that are typically freestanding or wall-mounted. The construction of these high speed fans and the speed at which their blades move make them unavoidably noisy. In fact, the fans can produce more than 85 decibels of noise, sometimes requiring hearing protection. While they do move a considerable amount of air, the air is circulated directly in front of the fan, providing some cooling in limited areas with little mixing of air or heat recirculation, the thermal differential that naturally occurs as heat rises. Moreover, the high velocity of the air moved by these smaller fans is uncomfortable and disruptive for people and, in agricultural settings, for animals stationed directly in the airflow stream. Finally, the sheer quantity of the smaller fans needed to make a large space comfortable create additional safety concerns, equipment maintenance and operating cost issues.

With their superior airflow, energy efficiency, and quiet operation, large, low velocity fans rapidly gained acceptance in agricultural settings, and also were quick to be adopted as a cooling alternative for spaces where air conditioning was impractical or too expensive. Today, HVLS fans are recognized as a technology with wide application and proven results in reducing or eliminating the cost of mechanical cooling for large spaces.

Operating Principles

Air is stratified into warm and cool layers, with the warmest air rising to the ceiling. It is not unusual for the temperature at the ceiling in tall, heated spaces in the winter to be 10 to 20 degrees Fahrenheit warmer than it is at floor level. Proper use of large, low velocity ceiling fans can virtually eliminate this stratification by gently driving the ceiling air downward and properly mixing the air to eliminate hot and cold spots. Using large, low velocity fans to maintain a constant air temperature throughout the space, building operators can reduce heat loss through walls and the roof and save up to 30% on heating costs. Moreover, during seasonal transitional periods, large, low velocity fans can be run on slow speed to bring the heat down from the ceiling, delaying startup of the heating system in the fall and enabling early shutdown in the spring.

With their slow turning, quiet, non-disruptive air movement, HVLS fans are increasingly used in office spaces. For Jonathan Arnold, founder of Arnold Imaging, the concern was heating an office that has 20-foot ceilings, uninsulated concrete floors and four 16-foot wide garage doors that flank the space. Arnold was reluctant to heat the 10 feet directly below the ceiling to 90 °F to get the bottom of the space to feel remotely comfortable. With a large, low velocity ceiling fan, slow air movement gave Arnold Imaging the ability to push that heat back down in winter and reduce the average temperature of the space.

Arnold reports flipping on a switch and feeling the effect of having natural air, rather than cold or hot air. "Instead of having 25 separate fans running, there are two big fans that cover the whole office," says Arnold, who appreciates the aesthetic and energy-saving properties of a large fan. Smaller ceiling fans are designed to reverse direction, pulling warm air to the ceiling and across the walls. This can increase heat loss through the roof and also increases energy use as the fan must run at high speeds to move enough air. With large, low velocity ceiling fans, the fan is slowed – not reversed – to redirect warm air to the floor. Because the fan only operates at a fraction of its maximum speed, the hot air is pushed down without creating a draft (which typically occurs at 30 feet per minute).

In hot weather, fans are operated at the upper range of speed to create a cooling breeze. People are cooled by the breeze that is created, even though the temperature has not been lowered; it is this cooling effect that makes building occupants feel cooler and more comfortable. The circulation results in an even temperature throughout the area covered by the large fan, eliminating hot and cold spots that can often plague large spaces.

Large, low velocity ceiling fans worked to eliminate condensation on the aircraft. Photo Courtesy of Big Ass Fans®

Because large, low velocity ceiling fans effectively move air, they also result in improved air quality and can reduce condensation, mold growth and wet spots on floors. All of this makes the technology ideal for many large warehouses, distribution centers, and manufacturing plants as well as institutional, aviation and sports facilities.

Because large, low velocity ceiling fans effectively move air, they also result in benefits in improved air quality, and can reduce condensation, mold growth and wet spots on floors. All of this makes the technology ideal for many large warehouses, distribution centers, and manufacturing plants as well as some institutional, aviation and sports facilities.

The 10,000-square-foot Alcoa Fujikura Corporate Hangar located at the San Antonio International Airport houses one corporate jet year-round. Without air conditioning, the employees who perform regular aircraft maintenance used small, high-velocity fans to beat the heat. But with unforgiving summer temperatures, and problems with condensation forming on the plane, the small fans couldn't provide the air movement and cooling breezes they required. "Besides the hot and humid weather, when the plane would come back from altitude, it would be covered with condensation from the temperature differences and would be dripping well through the night," says Ron Hoffman, Aircraft Maintenance Manager. "On humid mornings the floor would be slippery from the moisture coming up through the concrete. Not only was it a nuisance, it was a maintenance issue, because that condensation can cause corrosion on the aircraft." The hangar's high-velocity floor fans were substituted with a 24-foot-diameter large, low velocity ceiling fan — a move that Hoffman claims resulted in a lower operative temperature, increased thermal comfort and immediate elimination of condensation on the incoming plane.

As an alternative to air conditioning, large, low velocity fans can improve airflow in warehouses and distribution centers where extreme temperatures can have a negative impact on products and employees. Bill Oliver owns Oliver Winery in Bloomington, Indiana, where the warehouse has 32-foot-high ceilings. Wine is stacked close to 20-feet high, exposing the bottles stored at the top to the warmest air which rises to the ceiling, a situation that can compromise the integrity of the wine. In balancing floor to ceiling temperature differences, "Regular ceiling fans were not doing the job," says Oliver, explaining that wine needs to be stored at temperatures in the upper 60s or low 70s °F. Changes in temperature will make the fluid expand and contract, creating different pressures in the bottle, with the change in temperature acting to prematurely oxidize the wine. "A steady temperature is as important as the right temperature," adds Oliver, who installed large, low velocity fans to remedy the problem and recommends them for any situation where uniform air temperature and movement is desired without the whir of multiple standard ceiling fans.

Advanced Technology Fans

The latest technology incorporated into the design of large, low velocity ceiling fans makes them virtually silent, increases the aesthetic options available for integrating the fan into the visual scheme of the environment and enables a greater variety of fan controls and decorative accessories.

Eliminating any noise from a large revolving machine that hangs high in the air is based on extensive engineering. The key to today's silent fans lie in their specially designed motors. Cutting edge research and development has replaced traditional gearboxes with high-powered, low speed electronically commutated motors. The advanced technology drives the blades of the large fan without relying on a gearbox, eliminating noise and potential oil leaks for an effortless experience.

This patented airfoil and winglet design decreases vortices at the tip, thus decreasing drag and energy use. The upswept winglet profile also pushes more air down to the floor over a greater area. Photo Courtesy of Big Ass Fans®

Other innovations are made possible by the onboard placement of the motor's integrated electronic control system, rather than the conventional remotely located variable frequency drive. Fans can be operated from a small and stylish wall-mounted LCD panel, providing operating status of the fan. Further, new technology permits the attachment of accessories such as lights, loudspeakers, and surveillance cameras on the bottom of the fan. Advanced, onboard diagnostics measure the temperature, balance and performance of the new models.

These new technology fans have 10 blades with a patented airfoil design optimized to produce large volume airflows at low blade speeds with a decibel reading less than that of an empty library. Turbulence is greatly reduced and quiet operation is enhanced by the aerodynamic design.

A large, low velocity fan in candy-apple red makes a dramatic statement. Photo Courtesy of Big Ass Fans®

These commercial fans were designed for clean, quiet applications not in sync with the more industrial nature of the typical big fan. The typical large, low velocity fan, designed for industrial and agricultural applications, generates noise from moving gears and from electrical control units. In a noisy warehouse situation, the noise of the fans would be negligible, but this is not the case in a sound-sensitive environment such as an auditorium or church. While industrial fans might provide non-industrial customers the air movement they desire, the industrial sound performance may not be something they prefer.

Specification Considerations

Aesthetics
Utilizing a large, low velocity ceiling fan in a space for air movement increases occupant comfort through air movement and increases the energy efficiency of the space, it can provide a striking aesthetic. Manufacturers have made possible a number of customization options. Airfoils can generally be powder coated in a wide variety of finishes and in virtually any color imaginable, and wood veneer wraps match the traditional décor of some spaces. Additionally, by minimizing the need for ductwork and diffusers to distribute conditioned air, these fans free up the ceiling and save money on material costs in new construction scenarios.

Space Concerns
More compact HVLS fans have been developed to deliver industrial-strength air movement in smaller spaces with ceilings as low as 12 feet. Building on the same technology that has popularized large diameter fans for more than a decade, the new commercial models are capable of covering nine times the area of a traditional, 52-inch ceiling fan while maintaining its energy-efficiency. A gearless, direct drive motor also allows the fans top operate inaudibly, ideal in educational and commercial spaces. This same technology is available in wet rated models with both ceiling and pole-mounted options, bringing the HVLS advantages to outdoor spaces.

With and Without an HVAC System
There are several considerations in specifying a large, low velocity fan in a particular space. One main consideration is whether or not an HVAC system is present. In a building without an HVAC system, the fan will be the primary means of supplying thermal comfort during the summer. This generally means specifying fans capable of generating sufficient air velocity at the occupant level, either through larger fans or a much greater number of conventional fans. However, when considering fan options and mounting heights, it’s important to determine air velocity achieved at the occupant level. Conventional fans typically can’t establish sufficient air velocities over large areas, making them ineffective for high-ceilinged spaces.

In a building with an HVAC system, the large, low velocity fan is part of the system, not the primary means of cooling. Generally, it is advisable to integrate the fans into the HVAC system via the building automation system, if the building has one. In many cases, large, low velocity fans can be used to help distribute the HVAC system air more evenly throughout the space, minimizing the need for extensive distribution ductwork, which can save on the HVAC system's initial cost and energy usage.

After undergoing a dramatic facelift in 2003, Wisconsin's Green Bay Packer's Lambeau Field became the new high-tech gateway to Packerland, with an atrium featuring 94-foot-high ceilings and towering glass wall. According to Mike Moynihan, HVAC Manager, even though the structure had two air handlers, all the hot air remained trapped at ceiling height, leaving occupants very cold at ground level when Wisconsin temperatures dropped. "We had our air handlers set to their highest capacity — 115 °F to 120 °F — and they still weren't doing what we needed them to do," says Moynihan, explaining that with the addition of three 24-foot-diameter large, low velocity fans, the facility could provide a comfortable temperature at floor level. "We gained the heat we needed. When it's 20 degrees or less outside, it's 68 to 70 degrees on the floor," Moynihan says.

As in the case of the Orange Peel, a live music club in Asheville, North Carolina, the ventilation system, which does not have a cooling component, was adequate until the space was at capacity — which happened frequently when big-name acts were on the premises. Then, airflow became restricted and the packed-in patrons were suffering. Dan Cochran, Production Manager/Technical Director of the facility, noted a 20-foot-diameter large, low velocity fan was added to supplement the facility's air handling system. "It saved a lot of money by allowing us to forego air conditioning," says Cochran, noting that the fan quickly cools down the occupants at capacity and helps dry the floor after cleanup. As every space is different, however, it is recommended that the manufacturer perform an evaluation to determine the best solution for the individual space.

Large, low velocity ceiling fans at Lambeau Field Atrium enabled air handlers to run at 70°F during winter events. Photo Courtesy of Big Ass Fans®

Code Compliance
Building codes are at a local level and are specific to each city. It is recommended that the bottom of the ceiling fan is at least 10 feet from the floor. Fan installation instructions provide for compliance with the National Electrical Code (NEC) and all local and national building codes, and should be followed completely in order to insure proper operation.

Energy Efficiency
The reduction of heating bills is one of the more significant benefits of using large, low velocity ceiling fans. Since thermostats are generally installed about 5 feet off of the ground, a heating system will attempt to maintain the air temperature reading at that height. Because warm air rises, a colder layer of air often rests below the 5 foot level, rendering a space uncomfortable. To improve occupant comfort, thermostats are set higher to compensate for the temperature discrepancy. However, higher thermostat settings increase heat loss through the roof and energy costs. In a space suffering from stratification, the floor temperature may be 65 °F with the ceiling temperature at 85 °F. In this instance, the average temperature in the space is 75 °F. With a large fan continually mixing the air, the temperature at floor level might be 65 °F and at the ceiling, it might be 67 °F for an average of 66 °F. It goes without saying that it costs significantly less to heat a building to a 67 °F average temperature than it does to heat it to an average of 75 °F. The rule of thumb is that for every degree of reduction in the average space temperature that is eliminated, approximately 2-4 percent of heating energy is saved.

Energy Costs
Energy costs for a large, low velocity fan are low compared to the most commonly utilized method of providing occupant thermal comfort, the traditional HVAC system. A 12-foot commercial fan running at full speed uses approximately .6 kilowatts (kW) and provides cooling for approximately 3,600 square feet. The same fan operating at two-third speed, which is a more typical speed for an office area, uses approximately 0.2 kW. In destratification mode, which is one-third speed, the same fan uses less than 0.1 kW. The energy savings using large, low velocity fans in air conditioned spaces are provided by resetting the thermostat up because of the cooling effect created by air velocity. One degree of thermostat reset equals a 3 to 4 percent reduction in cooling energy consumption. In an air conditioned space in the summer and/or the energy savings provided by destratifying a heated space in the winter will be dramatically greater than the cost of operating the fans.

The cooling effect of gentle air movement creates an effective temperature reduction of 8-10° F, permitting an increase in thermostat settings without loss of comfort. Source: ASHRAE's Thermal Comfort Tool. Photo Courtesy of Big Ass Fans®

Potential for LEED Points
Large, low velocity ceiling fans have the potential to help earn Leadership in Energy and Environmental Design (LEED) points from the United States Green Building Council, which encourages and accelerates global adoption of sustainable green building and development practices. Large, low velocity ceiling fans may be part of a design strategy that earns points in the Energy and Atmosphere, Innovation in Design, and Indoor Environmental Quality LEED categories. As a general rule, no single product can earn a point or meet the requirements of a prerequisite; the product is generally part of a system or overall strategy that earns the points or meets the requirements of the prerequisite. Ask the manufacturer for a detailed account of LEED credits that fans can be applied towards.

Large, low velocity fans took the place of air-conditioning at this North Carolina cultural center. Photo Courtesy of Big Ass Fans®

Installation

While installation instructions may vary by manufacturer, some benchmarks apply. Mounting bolts should use steel in a sheer strength of 400 pounds — or about three times the sheer force that even the strongest fans can create. Using locking nuts can prevent the nuts and bolts from loosening during operation. Precision extruded aluminum foils provide a rigid yet lightweight assembly. To keep the foils in place, airfoil retainers can be fastened to the hub by three locking bolts. Choosing a manufacturer with standardized processes, certifications or merits, such as ISO certification and UL listing of products (instead of individual components), can provide assurance of safety as well as quality. Always inquire about the testing processes and procedures to ensure the fan(s) you choose meets the rigorous design standards set forth by industry experts.

Multiple Features Ensure Safe Operation

Image Courtesy Big Ass Fans®

Necessary Space Above the Fan
The minimum amount of space above the fan depends on its size. Large, low velocity ceiling fans generally need 2 to 7 feet of space above the top of the winglets. Installing fans closer than the recommended distance from the ceiling may result in less than optimum performance. For the foils, a minimum clearance of 2 feet in all directions the is recommended for safety and performance; an additional 2 feet is needed at the tips of the foils. Ideally, the fan should be placed inside the lighting grid at the same height as the lights or slightly higher, or replace the lighting fixture with a fan-mounted light.

NASA's Langley Research Center uses large, low velocity fans to keep hangars comfortable and aircraft safe. Photo Courtesy of Big Ass Fans®

Height Above the Floor
The ideal height of the fan above the floor is roughly one to two times the fan’s diameter. In reality, most fans are between 15 and 30 feet above the floor, although even that is not always possible. Mounting a large, low velocity fan with the bottom of the fan anywhere between 10 and 125+ feet above the floor can produce satisfactory results. Height, dimensions and square footage need to be taken into account when choosing the most appropriate model for a space. In tall, open spaces a larger diameter fan is typically needed to produce adequate air movement. Consult a fan expert to determine the appropriate fan size and mounting height for your application and desired results.

Fan Controls
Rather than wire the fan through the on/off switch, a fan controller is necessary for several reasons. The primary function of the fan control is to protect the fan motor and gear reducer (with gear-driven models) from destructive electrical and mechanical forces. The variable speed drive such as a VFD that most large, low velocity ceiling fans use, does not allow the fan motor to be damaged by running a current that is higher than it is capable of tolerating. It also stops and starts the fan gradually so the gear reducer is not subjected to excessive torque loads. In addition, the fan can be connected to the Building Automation System via the controller. And, in many cases, the fan controller is necessary in order to maintain the manufacturer's warranty.

Reversibility of Fans
Conventional ceiling fans are typically run in reverse because small fans cannot efficiently move air at very low speeds. Operating a small fan in reverse means that the high-velocity air from the fan moves across the ceiling, down the walls and finally reaches the occupants. By the time the air has traveled the distance from the fan to the occupant, the air is usually moving at a non-perceptible velocity — in other words, not causing a draft.

If the fan is designed to operate efficiently at very low speeds in the forward direction, as some large, low velocity fans are, there is no need to reverse the fan. Simply turning the fan slower in the forward direction will provide enough air movement to turn the air in the space over and reduce the stratification without causing drafts. By using running it in the forward direction, the fan will use two to four times less energy than a reversed fan.

It is also worth noting that if the airflow from the ceiling fan is reversed with airflow upward, even at lower speeds, the velocity of air across the ceiling above the fan is fairly high, typically around 400 fpm. However, if the ceiling fan is running at low speed with airflow downward, the airflow across the ceiling is low, typically 80 fpm or less. In short, reversing the air flow direction from ceiling fans in winter will cause the heat loss through the ceiling to increase. This means that more heat will be lost out of the ceiling, thus reducing the energy savings by destratifying the space.

Maintenance

Architects interested in determining the full life cycle cost implications of a fan will note that maintenance of the large, low velocity fan is minimal. Typically, it involves merely an annual dusting and inspection. An annual inspection would ideally involve the following:

• Check for the presence of the safety cable and shackle. The cable should be wrapped around the I-beam/angle irons, leaving as little slack as possible. The shackle should be securely tightened and located on the topside of the I-beam/angle irons.
• Ensure all mounting bolts (12x) are present and torqued to 98 ft·lbf (133 N·m). Ensure the lower cable is between the brackets of the lower yoke.
• Inspect motor terminations inside junction box and tighten if necessary.
• Check all connections in the fan controller and tighten as needed.
• Check gear reducer for oil leakage.
• Ensure all bolts (20x) securing airfoils to fan are present and torqued to 29 ft·lbf (39 N·m).
• Ensure airfoils are secured to one another by airfoil retainers (10x).
• Ensure bolts securing hub safety clips are present and torqued to 29 ft·lbf (39 N·m).

Additional Considerations

• Verify proper fan rotation. The fan should be turning counterclockwise when viewed from the floor.
• Dust airfoils, motor, and motor housing. If desired, use a gentle cleaner or degreasing agent to polish the foils.

Conclusion

Heeding the current focus on sustainable, energy-efficient design, large, low velocity ceiling fan manufacturers have made available a number of cost-effective cooling options that can work well aesthetically in any environment. Visually striking fans that are silent and capable of moving air effectively in summer, winter and transitional seasons can form a viable part of any structure's energy program.

Since its founding in 1999, Big Ass Fans® has designed and manufactured 6-foot to 24-foot diameter industrial grade ceiling fans. Their energy efficient design keeps operating costs at just pennies-per-day. With over 30,000 fans in operation, Big Ass Fans® is the authority on innovative air movement solutions. www.bigassfans.com