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December 21, 2011 -
High volume low speed fans (HVLS) were invented to keep cows cool in barns, but they've been increasingly adopted in the commercial facilities realm. They can move a lot of air with very little power. Plus they look cool, it's this huge fan, with some models having a kind of industrial chic thing going on.
Dan O'Connor, chief technical officer with AON Fire Protection Engineering, recently spoke on HVLS' impact on automatic fire sprinkler systems for NFPA's Fire Protection Research Foundation. In his presentation, High Volume Low Speed (HVLS) Fan and Sprinkler Operation Research Program Phase II, the scenario he spoke on was a warehouse setting, with boxes of goods stored on racks.
At the heart of the findings of his research is that if the fan or fans are not shut off during a fire, the automatic fire sprinkler system will extinguish the fire, but not before some significant damage has occurred. In one scenario tested with no fan-shut off, between five and 12 pallets were damaged and the fire jumped aggressively across an aisle. In the "fan on" tests, 12 sprinkler heads went off.
In contrast, when the fans were shut off, between a half and two and a half pallets were damaged and only four sprinkler heads activated. Now there were a lot of very specific parameters that you'll have to check out the original research for, but the conclusion was that sprinklers can protect with fan shutdown no later than 90 seconds after waterflow of the first sprinkler. It can take a fan up to a minute to stop rotating after it's shut off. Acceptable ceiling height depends on sprinkler type.
From this research the following proposals are being made for NFPA 13, under the General Design Criteria.
- Fans can have a max diameter of 24 feet.
- The fan has to be centered between four adjacent sprinklers.
- The vertical clearance from HVLS fan needs to be a minimum of 3 feet.
- All HVLS fans have to be interlocked to shut down upon receiving waterflow signal.
High Volume Low Speed (HVLS) Fan and Sprinkler Operation Research Program Phase II