High-volume low-speed fan

6 blade HVLS fan installed in a restaurant in Texas, USA.

A high-volume low-speed (HVLS) fan is a type of mechanical fan used in commercial and industrial settings. HVLS fans are generally ceiling fans although some come as pole mounted fans, and have diameters between 8 and 24 feet. HVLS fans move very slowly, and can move large amounts of air at low rotational speed– hence the name "high volume, low speed."

HVLS commercial ceiling fans can be found in livestock barns, warehouses, distribution centers, shopping malls, skating rinks and health clubs. HVLS fans are often used to supplement HVAC systems, as they provide a stronger cooling effect while helping to maintain a constant temperature and humidity.

History

In 1995, Walter K. Boyd, a lifelong inventor, was charged with developing a system to cool dairy cattle. When dairy cattle get too hot, they stop eating, which decreases or halts milk production.[1] Using the laws of physics, Boyd developed what is known today as the HVLS (high volume, low speed) fan;[2] Boyd’s fan was 20-feet in diameter with 10 aluminum blades.[3] Instead of moving quickly, the fan blades moved very slowly.

After much testing, Boyd and other researchers concluded that the new HVLS fan technology reduced heat stress in cattle as well as reducing energy costs.[4]

Definition

An HVLS fan has two requirements in order to be labeled as such:

  1. The volume of air passing through the fan in one single revolution must be no less than 500 cubic feet.[5]
  2. The tip speed of the fan’s blades must not be greater than 60 miles per hour.[5]

How HVLS fans work

Example of an Airfoil

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.[6]

Under ideal conditions, an 8-foot fan produces a floor jet of air approximately 36 inches deep. A 24-foot fan produces a floor jet 108 inches deep, tall enough to engulf a human standing on the floor or a cow, its initial development purpose.[6]

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.

Large fans versus small fans

6 blade HVLS fan in a warehouse, USA.

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.[6]

The perimeter of an air column varies directly with column diameter. And 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 three-foot diameter fan, therefore, has more than six times as much “friction interface” per cubic foot as does the air column from a 20-foot fan.[6]

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.[6]

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.[6]

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

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. A fan’s CFM should be posted on a fan’s packaging or spec sheet. To measure the performance of an HVLS fan, engineers generally use the method approved by the Air Movement and Control Association (AMCA) and measure “thrust,” which is the force the fan produces as a result of the air being pushed through it.

For comparison purposes, a 52″ residential ceiling fan has posted 5,873 CFM,, whereas an 8-foot HVLS fan, has an AMCA-certified CFM 53,623 CFM.[7]

Heating and cooling benefits

Ceiling fans are considered the most effective of these types of fans, since they effectively circulate the air in a room to create a draft throughout the room. When used with air conditioning, a ceiling fan allows the raising of the thermostat setting about 4°F with no reduction in comfort.[8]

Studies by mechanical efficiency experts show that HVLS fans are the most energy efficient air circulating fans available.[6] When used as a stand-alone cooling system, HVLS fans provide a cooling effect equal to a reduction in temperature of up to 8°F. within the fan’s coverage area of up to 20,000 sq. ft. per 2 horsepower 24-foot fan.[6]

In most commercial and industrial buildings, heaters are mounted overhead so as to not interfere with working space. Unfortunately, this results in a heat gradient differential or heat stratification of 10 degrees F to 35 degrees F from the floor to the ceiling depending on the height of the ceiling. While running an HVLS fan in forward mode will draw heated air down, more air is drawn in from the sides of the fan than the top, leaving some warm air undisturbed close to the ceiling.[6]

Running an HVLS fan in reverse clears warm air off the ceiling, pushing it to the walls and down to the floor, which provides a more even distribution of heat from top to bottom – especially important when people are working at different levels within a generally open structure.[6]

References

  1. ↑ Keown, Jeffrey. "How to Reduce Heat Stress in Dairy Cattle". University of Missouri, Extension. Retrieved 1993. Check date values in: |accessdate= (help)
  2. ↑ Boyd, Walter. "Walter Boyd Talks About HVLS Fan Technology". Plant Services. Retrieved 2011.
  3. ↑ "HVLS History". MacroAir Technologies.
  4. ↑ House, Harold. "Large Ceiling Fans Offer Energy-Saving Way to Reduce Dairy Cow Heat Stress". Ontario, Ministry of Agriculture, Food and Rural Affairs. Retrieved 2003.
  5. ↑ 5.0 5.1 "Defining HVLS". MacroAir Fans.
  6. ↑ 6.0 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 Tetlow, Karin. "HVAC for Large Spaces: The Sustainable Benefits of HVLS Fans". McGraw Hill Construction.
  7. ↑
  8. ↑ "Ceiling Fans and Other Circulating Fans". Energy Efficiency and Renewable Energy. U.S. Department of Energy. Retrieved February 9, 2011.

External links

Wikimedia Commons has media related to HVLS fans.