Large, Low Velocity Fans: Making Energy Efficiency a Breeze

Advanced, good-looking solutions for air movement in large spaces
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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.

 

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Originally published in Architectural Record
Originally published in August 2011

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