HVLS fans were originally used in Australia in the dairy industry to help keep humidity low for the cattle. When the original design was introduced in Australia, it was mandatory for the HVLS fans to be interlocked by a Very Early Smoke Detection Alarm (VESDA) system for early fan shutdown.
When the fan made it over to the USA it was perceived as a very “green” way to cool a warehouse or plant. The “green” folks liked the design because the fans could be run on a 1 HP motor and can provide a huge amount of air circulation for a very cheap energy cost. The problem is, the VESDA technology was not part of the original design in the USA.
What is a HVLS Fan? The fans typically have 4 – 12 blades that are between 6 ft. and 24 ft. in diameter. They are usually run at speeds, between is 24 and 66 rpm. It takes up to 10 minutes to shut one fan down. A fan running at 66 rpm with 24 ft. diameter blades displaces 370,000 cfm (175m3/s).
As fire protection engineers, we can see a major problem because the HVLS fan can negatively impact the automatic sprinkler operation during a fire. In fact some Fire Marshalls have outlawed HVLS fans from being installed in any of their towns. A Fire Marshall in a town close to our main office in northern Bergen County, NJ will not allow HVLS fans to be installed. This particular town has a significant number of warehouses and supports one of the largest seaports in the USA.
Over the past five years there have been many studies conducted by Schirmer Engineering (now Aon Risk Services) Zurich Insurance, CNA Insurance, XL Insurance and others, all with varying differences. Below are two examples of test results that were conducted where the fans were not interlocked:
Fire Test 1
- Cartoned expanded group A plastic
- 15 ft. high storage on pallets
- Ceiling is 25 ft.
- K = 11.2
- Sprinkler system is designed properly per NFPA
- Fire started on lowest carton 10 ft. off center from the center of the HVLS fan
- 73 heads opened between 3′:26″ and 7′:35″
Fire Test 2
- Class II commodity
- 12 ft. storage on pallets
- Ceiling is 25 ft.
- K= 5.6
- Sprinkler system is designed properly per NFPA
- Fire started on lowest carton 10 ft. off center from the center of the HVLS fan
- 21 heads opened
FM Global conducted a burn test at its Test Center in Rhode Island and published its findings on January 2011. The test was conducted in conjunction with Property Research Group (PIRG) and was directed through the National Fire Protection Association (NFPA). The Technical Report was called, Impact of a High Volume Low Speed Fan on Sprinkler Performance on Rack Storage Fires.
The HVLS fan had 6 blades, a fan diameter of 24 ft. and operated at 66 rpm, which displaced 370,000 cfm. There was a 10 ft. clearance between the top of the storage array. The test results concluded that automatic sprinkler systems would fail to control a fire if the fan was not shut down within 90 seconds of the activation of the first automatic sprinkler.
There are two design areas for HVLS fans and automatic sprinkler systems that need to be carefully checked. They apply to both for storage and non-storage occupancies:
- The HVLS fans need to shutdown within 90 seconds after the first sprinkler operates. This can be achieved by interlocking the fans with waterflow alarm devices, smoke detection devices or heat detection devices. When detectors are used they should be installed and spaced uniformly above the fan blade area. The NFPA and/or FM Global standards apply for automatic fire detection installation.
- The fan support structure and the drive assembly should be installed so that it does not obstruct the discharge pattern of the sprinklers. Refer to FM Global DS 2-0, “Installation Guidelines for Automatic Sprinklers” or NFPA 13, “Standard for the Installation of Automatic Sprinkler Systems.”
Risk Logic, Inc. can help you determine the best approach to shut down HVLS fans as improper shutdown can result in a total loss at your facility. Please contact us for additional information