Condensation occurs intermittently in many naturally ventilated buildings. Condensation will occur on a surface when the temperature of that surface falls below the dew point temperature of the ambient air. This can contribute to mold growth and the risk of injury to employees from slipping on wet floors, both of which can lead to serious health implications and loss of time at work.

To prevent condensation without air conditioning the space, one remedy is to raise the temperature of the air in locations where condensation has occurred. Raising the temperature of the air increases its moisture capacity, reducing its relative humidity. Destratification using giant, high-volume, low-speed industrial ceiling fans is a simple cost-effective way to increase air temperature near floor level.

Distribution centers typically have concrete floors on earth fill. In many locations, particularly during springtime, the surface temperature of the concrete floor is below the dew point temperature of the ambient air, thus creating condensation on the floors.

For example, in springtime in northern Georgia, the concrete floor slab surface temperature is similar to soil temperature at a depth of about 6 feet under the paved surface outside the building. This soil temperature tends to lag the seasonal rise in springtime outdoor air temperature by about 30 days due to the heat capacity of the earth.

Cool floor temperatures pose safety hazards both to people walking on the wet floor and operating moving vehicles, such as forklifts and skid steer loaders. The increase in air temperature required to prevent condensation is often only 1 degree or 2 degrees. This temperature adjustment can be achieved without additional heating equipment by destratifying (mixing) the air in the building.

In spring, the air under the ceiling is warmed by solar heat from the roof. Destratification using industrial ceiling fans blends this warm air with cooler air near floor level. The temperature of the mixed air is typically warm enough to prevent condensation on the concrete floor.

Other applications for destratification for condensation control include material surface treatment processes in manufacturing. Surface coating of sheet glass or painting or galvanizing sheet steel is often compromised by condensation or rust staining prior to treatment. Such facilities have benefited from destratifying the air inside each building using large industrial ceiling fans to avoid moisture accumulation.

The advantages of using high-volume, low-speed fans to prevent condensation include low fan noise level and lower air velocities at head height. (Local air velocities greater than 40 fpm at head height are likely to result in complaints of drafts from building occupants.) For instance, the Powerfoilâ„¢ fan from Big Ass Fans is designed to improve worker comfort in the summer by moving 334,000 cfm of air, and lower heating costs in the winter by effectively mixing the warm air suspended near the ceiling with the cooler air at floor level.

Research at Big Ass Fans points out that fans can cover an area approximately 20,000 square feet for about 10 cents an hour, and contribute to the overall facility safety program.

Richard Aynsley, Ph.D., M. ASHRAE, is director, Research & Development, Big Ass Fans Co., Lexington, Ky.

Publication date: 10/17/2005