In the late 1990s, 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]

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]}

Large fans versus small fans edit

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]

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.

Measuring fan performance edit

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 1999 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.

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]

Improved Air Circulation: High-Volume Low-Speed (HVLS) fans move large volumes of air at a low speed, creating a gentle breeze that helps distribute air evenly throughout a space. This eliminates hot or cold spots, ensuring more consistent temperatures.

Energy Efficiency: HVLS fans consume less energy compared to traditional high-speed fans or air conditioning systems, while still providing effective air movement. This leads to lower heating and cooling costs.

Enhanced Thermal Comfort: The gentle breeze from HVLS fans helps occupants feel cooler in warm environments and reduces the feeling of stuffiness. In cooler environments, they distribute heated air more evenly, improving overall comfort.

Moisture Control: HVLS fans reduce condensation and humidity levels by circulating air and preventing moisture buildup. This is especially beneficial in spaces like warehouses, gyms, or swimming pools.

Reduced HVAC Load: By improving air circulation and distributing air more efficiently, HVLS fans reduce the workload on heating and cooling systems. This can extend their lifespan and reduce maintenance costs.

Noise Reduction: HVLS fans operate at lower speeds, resulting in quieter operation compared to high-speed fans. This creates a more comfortable and peaceful environment for occupants.

Overall, HVLS fans are a cost-effective and energy-efficient solution for improving indoor air quality, thermal comfort, and energy savings in various applications.

• Air Movement and Control Association