Heat Stress and Cooling FansJun 30th, 2013 | By Nina Wolgelenter | Category: Quick Reads
People, like machinery, tend to break down in extreme conditions. As temperatures rise, productivity falls, safety becomes questionable and comfort is no longer. Heat stress is defined as a group of conditions that result from being overly exposed to heat or overexertion in excessive ambient temperatures, a common occurrence in industrial spaces during the summer months. Air movement through the use of high volume, low speed (HVLS) fans help combat these adverse conditions in a cost-effective, energy-efficient way.
The sensation of feeling comfortable is not just dependent on air temperature, although that is a strong contributing factor. Human thermal comfort takes into account numerous environmental factors including temperature, thermal radiation, humidity, and air speed along with personal factors including metabolic rate and amount of clothing. When temperature and humidity rise, the body’s ability to cool itself decreases.
Studies indicate an average reduction of 2 percent in work performance per 1.8 degree Fahrenheit (F) temperature rise when the temperature is above 77 F. While this may not seem detrimental on an individual basis, the drop in employee productivity can add up to huge profit loss across a company.
Gentle, non‐disruptive, non‐turbulent airflow from HVLS fans promotes the body’s natural cooling process, helping to maintain comfort in hot and humid conditions.
How HLVS Fans are Different
Properly engineered HVLS fans take advantage of their immense size—not speed—to move massive amounts of air. When the airfoil length is doubled, the surface area that those airfoils sweep increases by a factor of four. As the size gets larger, the amount of air the fan moves increases at a much faster rate than the amount of power it takes to turn the fan. With all things being equal, a larger fan, up to 24 feet in diameter, becomes more efficient. Additionally, air fences can be installed along the airfoil to direct air that would otherwise slide off and be lost. With the correct size, number, and placement of fans, thorough air movement is achieved, eliminating any dead spots or stagnant air that might otherwise exist in a facility.
Maintaining Summer Comfort
In applications requiring cooling, fans operate between 60 percent and 100 percent of maximum speed improving comfort and productivity with an evaporative cooling effect mentioned above as well as the added effect of heat transfer when skin temperature is warmer than air temperature. Although fans do not lower the temperature of a space, the perceived cooling effect can make a person feel up to 10 Fahrenheit degrees cooler in non-air conditioned spaces.
Working conditions at Top Notch Distributors in Earth City, Missouri, U.S.A., were such that ice water stations and floor fans were scattered about the 60,000 square foot warehouse to help ease summer discomfort. On a 105 F summer day, temperatures near the roof deck soared to 115 F within the facility.
HVLS fans that were 24 feet in diameter were installed to produce a column-shaped jet of air roughly equal to the diameter of the fans. As this jet struck the floor, it spread out in all directions, displacing the stagnant air and setting up a convection-type circulation pattern. Air from the floor level was moved out towards the walls or obstructions and then back up into the fan to be recirculated. HVLS fans provide up to a 10 F cooling effect, significantly reducing the heat stress on workers and making their environment safer, more productive, and more comfortable.
Lost productivity is a double-edged sword; imagine a warehouse averaging 85 F during the four summer months. At 85 F, each employee loses 8.8% of their productivity. With 30 full-time employees earning US$ 15 per hour, US$ 1,500 is lost in weekly productivity. The total loss in productivity per summer comes to approximately US$ 27,000 (not including the costs of inefficient cooling, worker compensation claims due to heat stress, and increased absenteeism on hot days). If air movement is incorporated into the space via HVLS fans, the warehouse will feel at least 10 degrees cooler, allowing the company to recover about two thirds of productivity lost without the fans.
To compound the issue, less productive workers produce fewer products. If you consider an assembly operation where workers assemble products worth US$ 45 of revenue to the company at a rate of 14 items per hour, then instead of each worker making 112 assemblies per day, they make closer to 100, at a loss of over US$ 500 in revenue. It’s easy to see how this loss in productivity can ruin your summer financially.
Reduced Energy Consumption
Energy usage is dependent on the size and number of fans, horsepower of the motors, and hours of operation. With typical hours of operation during the summer months, a 12-foot to 24-foot HVLS fan uses on average 7.1 to 11.6 kilowatt hours of energy on a daily basis, far less than an air conditioning system, and far more practical in most warehouse facilities.
About the Author
Nina Wolgelenter works for Big Ass Fans, the world’s preeminent designer and manufacturer of large-diameter, low speed fans.
Photograph: HVLS fan installed at Aaron & Co. warehouse, courtesy of Big Ass Fans.