by Jonathan Hollist
In 1998, dairy farmers were looking for a way to cool their cows and reduce heat stress. Air-conditioning was too expensive and it was impossible to run the ductwork in the barns. Small barn fans helped, but did not cover a wide enough area, consumed excessive and costly energy, and required ongoing maintenance. Engineers based at a fan manufacturer created a huge unit with blades spanning 7.3 m (24 ft) instead of the typical 1.5 m (5 ft). To offer a gentle breeze, the fan speed was a fraction of that of small fans. Thus, high-volume, low-speed (HVLS) fans were born.
Contrary to popular belief, not all ‘large fans’—defined in U.S. Department of Energy (DOE) testing as those larger than 2.1 m (7 ft) in diameter—are true HVLS systems. A fan must meet certain criteria to be labeled as such. The volume of air passing through the fan in one single revolution must be no less than 14 m3 (500 cf), and the speed at the tip of the blades must not be greater than 97 km/h (60 mph).
The first big industrial ceiling fans employed 10 blades. However, after extensive aerodynamic testing, designs have been re-engineered, with models using anywhere between eight and two wing-shaped blades to result in the most efficient air movement using less energy and motor torque, and reduced wear and tear on the fan.
Benefits of HVLS fans
An HVLS fan is a ceiling-mounted fan, with size being the most notable difference between it and a traditional unit. While typical high-speed fans are usually between 0.9 and 1.2 m (3 and 4 ft) in diameter, HVLS fans are 2 to 7.3 m (6 to 24 ft). The difference in size is not an accident, as these larger blades move much larger amounts of air. This is beneficial in industrial and commercial settings, since more people inhabit these buildings. Conversely, smaller high-speed fans work twice as hard, expelling larger amounts of energy to cover only a fraction of the square footage, due to the smaller blades.
The benefits of big industrial ceiling fans go beyond the massive amounts of gentle, comforting air. The lower speeds required by smaller motors allow for an incredibly efficient cooling effect at a lower cost. When paired with heating units and air-conditioners, the fans cut down energy consumption by allowing businesses to turn the heating and cooling systems down or off.
HVLS fans provide environmentally sound solutions for warehouses and other commercial buildings. They enable equipment and inventory to be stored in a more hospitable environment (increasing product longevity), while helping to protect and sustain the natural environment. Many businesses are looking toward green practices, not only to better the environment and their communities, but also because the government now provides rewards and incentives for these intelligent practices. When Leadership in Energy and Environmental Design (LEED) certification is required by a local code or government agency, HVLS fans have helped projects achieve certification within the Indoor Environment Quality (EQ) and Energy and Atmosphere (EA) categories for, respectively, their ventilation capabilities and energy efficiency while maximizing HVAC effectiveness.
On a practical level, HVLS fans are more comfortable to have in a room due to the low amount of noise emitted. (The company with whom this author works has performed tests where the sound sensor is 1.5 m [5 ft] above the ground and 6.1 m [20 ft] from the center of the fan, which is 6.1 m high. The decibel ratings for these tests comes in between 50 and 60 dBa—about the same noise level as normal speech.) Smaller fans that move faster work overtime to cool a room for long periods, creating more noise. Not only does the motor on a smaller fan have to work harder to create the high speed, but the fan blades also spin faster, creating more of an uncomfortable, chilly environment.