In the late 1990’s, dairy farmers were looking for a way to reduce heat stress on their cows, but providing air conditioning in a barn was not economically feasible, and small box fans did not provide the coverage needed.

The HVAC industry responded with a new type of “ceiling fan” that had very large blades to move a large volume of air while using a low fan speed. These High-Volume-Low-Speed (HVLS) fans created a gentle breeze instead of the turbulent, high-velocity air jet produced by a smaller, high speed fan that dissipates quickly over a short distance.

Commercial HVLS fans differ from residential ceiling fans with regard to diameter, rotational speed, and performance. These very large, low-speed commercial fans are more efficient and effective than small high-speed fans because their large volume air movement can have a significant influence on thermal comfort.

Not all “large fans” are HVLS fans. One manufacturer describes the defining HVLS features as follows:

  • The volume of air passing through the fan in one single revolution must be no less than 500 cubic feet.
  • The top speed of the fan’s blades must not be greater than 60 miles per hour.

HVLS fans proved to be a huge success because the lower speeds require smaller motors and allow for an incredibly efficient cooling effect at a much lower cost.

It wasn’t long before these fans began showing up in places other than dairy barns, like industrial manufacturing and warehousing facilities, retail stores, schools, offices, and churches.

Their increasing presence in various buildings soon caught the attention of the fire protection industry with concerns about:

  • Whether the blades would create obstructions to sprinkler discharge
  • Whether the significant mixing of air would change the typical formation of the fire plume and ceiling jet, delaying actuation of sprinklers
  • How the significant downward column of air and horizontal floor jet created by the HVLS fans would affect the intensity of a fire

To study this problem, HVLS fan manufacturers, insurance companies, and fire protection engineering consultants came together to complete a two-phase study to generate recommendations that could be incorporated into sprinkler standards and guidelines to ensure sprinkler protection wasn’t being sacrificed at the expense of occupant thermal comfort.

The HVLS study was guided by a collaboration between the Fire Protection Research Foundation and the Property Insurance Research Group. The first phase of the study was conducted by Schirmer Engineering Corporation and their report was issued in February 2009. Click here for details and findings from Phase I of the study.

The second phase of the study was conducted by Factory Mutual Research Corporation and their final report was issued in January 2011. Click here for details and findings from Phase II of the study.

The information gleaned from this two-phase study ultimately resulted in changes to NFPA 13- Standard for the Installation of Sprinkler Systems (2013 Edition). NFPA 13 (2013 edition) addresses the requirements for installation of HVLS fans in buildings equipped with sprinklers in Section 11.1.7 and Section 12.1.4 as follows:

  1. The maximum fan diameter shall be 24 ft (7.3 m).
  2. The HVLS fan shall be centered approximately between four adjacent sprinklers.
  3. The vertical clearance from the HVLS fan to sprinkler deflector shall be a minimum of 3 ft.
  4. All HVLS fans shall be interlocked to shut down immediately upon receiving a waterflow signal from the alarm system in accordance with the requirements of NFPA 72.

The study also resulted in Engineering Bulletin 02-11 being added as a supplement to Factory Mutual Data Sheet 2-0 in March 2011. This Supplement addresses the requirements for installation of HVLS fans in storage and non-storage occupancies equipped with sprinklers as follows:

  1. Provide a means of automatic shutdown for all HVLS fans. Design the automatic shutdown so that power to the fan is interrupted within 90 seconds after the first sprinkler operates. FM Approved smoke detection devices, heat detection devices, and water flow alarm devices are acceptable means to achieve automatic shutdown of fans. When detectors are used, install and space them uniformly above the fan blade area. Follow the recommendations in DS 548,Automatic Fire Detection, and the manufacturers spacing requirements.
  2. Arrange the installation of HVLS fan so that the fan support structure and the fan drive assembly do not obstruct the discharge pattern of the sprinklers. Refer to DS 2-0 for general guidelines. 

If you are looking to move a lot of air and improve occupant comfort, HVLS fans may be an economical answer. Just remember to follow the applicable guidelines noted above to guard against adverse effects on your sprinkler protection!