Understanding the Risk
A high-volume low-speed (HVLS) fan is a type of
mechanical fan used in commercial and industrial
premises. HVLS fans are generally ceiling fans although
some come as pole mounted fans. Unlike residential
ceiling fans that are typically 36- to 52-inches (91 to 132
cm) in diameter, HVLS fans have very large diameters
that start at 8 feet (2.4 m) and go up to 24 feet (7.3 m).
Unlike standard high-speed fans, HVLS fans move very
slowly. With very low rotational speed, HVLS fans move
large amounts of air – hence the name, high volume, low
speed.
HVLS ceiling fans can be found in warehouses,
distribution centers, shopping malls, skating rinks and
health clubs to name a few. Due to the rising costs of
energy, 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.
Air Flow of Typical HVLS Fan
This air flow effect can cause problems when it comes to
fire protection and automatic sprinkler operation. The
downward air-flow can delay the operation of sprinklers
by not allowing the heat from a fire to rise through the air
flow and operate the sprinkler heads in the required area
over the seat of the fire. The fan itself can also create
obstructions to the sprinkler water spray pattern. Both of
these factors can have a negative impact on sprinkler
operation and effective fire suppression.
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. (14.2 cubic meter)
2.
The tip speed of the fan’s blades must not be
greater than 60 miles per hour (96.5 kilometer per
hour).
How the HVLS Fans Work
HVLS fans work on the principle that a breeze moving
across your skin on a very hot day feels good. The cool
moving air breaks up the moisture-saturated boundary
layer (also known as perspiration) surrounding the body
and accelerates evaporation to produce a cooling effect.
No matter their size, 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.
Under ideal conditions, an 8 foot (2.4 m) fan produces a
floor jet of air approximately 36 inches (91 cm) deep. A
24 foot (7.3 m) fan produces a floor jet 108 inches (274
cm) deep, tall enough to engulf a human standing on the
floor.
AIG Insight | small print sub text Arial 7.5pt
Typical HVLS Fan in warehouse occupancy
Installation Requirements
Based on the findings through numerous large scale
tests using both standard spray sprinklers and Early
Suppression Fast Response (ESFR) sprinklers it was
determined that the HVLS fans do have a negative
impact on the effective operation of sprinkler systems.
Consequently, the installation of HVLS fans in buildings
equipped with sprinklers, including ESFR sprinklers,
shall comply with the following:
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1.
The maximum fan diameter shall be 24 feet (7.3 m).
Standards
2.
The HVLS fan shall be centered approximately
between four adjacent sprinklers.
The references are:
3.
The vertical clearance from the HVLS fan to
sprinkler deflector shall be a minimum of 3 feet (0.9
m).
NFPA 72, National Fire Alarm and Signaling Code
4.
At a minimum all HVLS fans shall be interlocked to
shut down immediately upon receiving a waterflow
signal from the automatic fire sprinkler system in
accordance with the requirements of NFPA 72.
Ideally, the fans should be interlocked to a fire alarm
device such as a smoke or heat detector in addition
to the waterflow device. A fire alarm device will
likely respond much soon than the waterflow signal.
This will help ensure that the fan is shut down
immediately. Connection to multiple devices will
also improve reliability of fan shut down.
NFPA 13, Standard for Installation of Sprinkler Systems
Additional Resources
For further information, contact your local GLP AIG Risk
Engineer
.
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