Large diameter, low speed fans produce a column-shaped jet of air roughly equal to the diameter of the fan. As this jet strikes the floor, it spreads out in all directions, displacing the stagnant air and setting up a convection-type circulation pattern. Air from the floor level is moved out towards the walls or obstructions and then moves up back into the fan to be recirculated. During cooling seasons the fan speed can be increased, so that faster-moving air working in concert with the body’s natural cooling process produces a cooling effect of up to 10º F. Conversely, during heating seasons the fan speed can be reduced so that the air continues to mix, moving hotter air at the ceiling down to occupant level without causing a draft. This destratification keeps occupants comfortable in heating seasons and significantly reduces heating costs.
The amount of energy saved by using a large diameter fan depends heavily on how much energy the building consumes. Generally speaking, savings on the heating side range from 15-30% of the energy used to heat the building (higher ceilings yield larger savings). On the cooling side, savings of 3-5% per degree the thermostat is raised are typical. The air movement from a large diameter fan can typically allow managers to increase their air conditioning set point by 5 to 7F (raising it from 72 to 78, for example) without occupant discomfort. This may seem like a minor increase, but could represent 25% of the energy needed to condition the space.
These fans have been custom-engineered and designed to suit the needs of specific applications, from a silent library to a large industrial space.
Let’s take a look at the different locations where fans are commonly used in school facilities.
Dining Halls and Lobbies
Large diameter fans are designed to circulate air throughout large and tall spaces, making them an ideal solution for efficiently improving comfort in student common areas.
While other schools in the Wasilla, Alaska, school district take three or four hours to heat up at the beginning of the school day, a 12-ft. diameter fan in a central atrium has made Machetanz Elementary School’s temperature recovery almost immediate. The fan increases the building’s efficiency and has significantly lowered its energy costs. Architects at McCool Carlson and Green projected the building would perform at 8,700 mBtu/year, but after the first full year of occupancy the building performed at 4,300 mBtu/year, representing over $200,000 in annual savings.
“The fan helped improve the indoor environment of the building with a passive strategy of reversing the convection and getting our hot air off the ceiling back down to a floor,” said Jason Gamache, sustainability coordinator with McCool Carlson and Green.
Natatoriums and Gymnasiums
In pool areas, large diameter fans are used to improve ventilation and maximize the efficiency of HVAC systems, solving complaints common to these facilities. Many issues with indoor air quality (IAQ) in natatoriums revolve around the type of chlorine used, community water supplies and insufficient air conditioning systems. One constant, however, is the need for air movement to help move the chloramine gases and keep the toxicity levels below 0.5 parts per million at the water’s surface, where the swimmers breathe in the concentrated bad air. In addition, the addition of air movement helps to reduce humidity and mold build-up, both inevitable in damp environments.
The University of Texas, Austin, is home to one of the original, largescale university aquatic facilities built in the U.S. The Texas Swim Center recently met the challenges of improving IAQ with an impressive ventilation system upgrade and the addition of large diameter, low speed fans. In contrast to air re-circulators that simply circulate the contaminated air in the space with no way for it to escape, engineers used fans and ventilation to exchange air completely overnight.
“We have a daily setting for these fans but at night, when we don’t have anybody in the facility, three things happen,” said Charles Logan, director of the Texas Swimming Center. “Release valves open up in the building, the fans are turned up to full speed and 100 percent outside air is brought in to flush out all the air that circulated throughout the day.”
For schools without air conditioning in voluminous gymnasiums and indoor practice facilities, fans can greatly improve the comfort and safety of student athletes.
Highland Park Independent School District invested in an indoor practice facility to get its football players out of the Texas summer sun. But louvers and warehouse fans, mounted just below the 36-ft. ceiling, provided ventilation and air movement at a level too high for the players to feel the benefit. Players were so uncomfortable in the sticky, stagnant facility that they asked to practice outside, despite temperatures reaching 150 F on their artificial surface.
Four 24-ft. diameter fans were added, providing serious air movement throughout the facility, from ceiling to floor and wall to wall. The fans’ upturned winglets create deep jets of air, keeping airflow moving up and over obstructions to reach every corner of the space.
“When you turned on the small fans, the players couldn’t hear me, because of the motors,” said Coach Randy Allen. “Now we can play the stereo and they can understand our coaching and I don’t have to talk so loud.”
Auditoriums, Libraries and Classrooms
For applications where low sound levels are critical, such as in libraries, noise from a fan system, which can include mechanical, electrical and aerodynamic, must be minimized. This is where a fan specifically designed to be used in commercial spaces shines. These fans operate slowly enough to avoid any aerodynamic noise, and direct drive motors are virtually silent mechanically and electrically.
The Oakland Unified School District, (OUSD) sought to comply with the ASHRAE Standard 55-2010 Thermal Environmental Conditions for Human Occupancy comfort criteria without using compressurized cooling in high-density occupancy rooms. Instead, they employed a three-layer strategy for maintaining comfort conditions, using a nighttime cooling cycle, thermal mass walls and large diameter fans specifically engineered for the space. In this system, the fans are used to, “drop the perception of temperature by four to five degrees, explained Brent Eubanks, mechanical engineer and LEED AP for Taylor Engineering, LLC. “If your comfort limit is at 78, it can be 83 degrees in the room and you’re still within your comfort threshold, thanks to the air movement by the ceiling fans.”
By installing large diameter, low speed fans over the summer break, facility managers can improve year-round energy efficiency and comfort conditions across campus. Whether your main goal is destratification for quicker warm-up times and energy savings, or elevated air speed for greater perceived cooling during warm weather, large diameter fans have you covered top to bottom.
is senior copywriter for Big Ass Fans. Based in Lexington, Ky., the Big Ass Fan Company is the world’s preeminent designer and manufacturer of large diameter, low speed fans for industrial, agricultural, commercial and residential use. For more information, visit www.bigassfans.com.