Air flow pattern in unenclosed area
The air flow comes down from the fan and reaches the floor, then turns it into a horizontal jet radiating out in all directions (figure 1). The depth of this floor jet varies depending on the size of the column – which is essentially the diameter of the fan – and the air velocity. A 20 ft. (6m) Big Fan at standard speed creates a floor jet about 9 ft. (2.7m) deep.

Air flow pattern in enclosed area
The floor jet radiates out horizontally until it reaches the walls. The walls turn the airflow upward in the same way the floor turned the down-flowing air outward. The ceiling then turns the upward flow inward, back toward the low pressure zone above the fan. This creates convection-like air currents that gather momentum. Once these currents are established, the fan is entraining far more air than is actually passing through it (figure 2).

Air flow pattern with multiple fans
Where there are multiple fans appropriately spaced, the expanding floor jets of adjacent fans meet to create a pressure zone which acts much like a wall, causing each fan to behave more like a single enclosed fan (figure 3). Typically, a single fan’s performance will increase markedly when a full complement of fans is added.

Air flow pattern with thin or streamlined obstruction
Obviously, obstructions on the floor tend to block the horizontally moving air. A thin obstruction, or a streamlined one, even if it is quite large, does minimal harm. The air tends to flow smoothly around these obstructions, losing little momentum, and leaving only a small stagnant area behind the obstruction (figure 4).

Air flow pattern with wide, blunt or flat-faced obstruction
A wide, blunt, or flat-faced obstruction, on the other hand, forces the air to change direction, turning upward and outward. The result is that the obstruction creates a stagnant area behind it that is wider and higher than the obstruction itself (figure 5).

Best practices
Here are some techniques, based on experience, that can make a dramatic difference in the congested areas of your facility.

1. Swap positions within work areas so as to put the workers in front of the obstructions instead of behind them. Similarly, consider swapping positions between work areas that are stagnant and areas of good air movement that normally don’t contain people.

2. Position large obstructions so that the smallest profile is perpendicular to the direction of air movement. For example, a sheet metal press brake might have five times the frontal area if it’s facing the airflow rather than if it’s turned sideways.

3. Wherever possible, position welding curtains, partitions, sheet materials, etc. in such a way as to scoop air into the work area rather than deflect it away.

4. Construct deflectors out of cardboard, canvas, sheet metal, or light plywood to steer air where you want it to go (figure 6). Deflectors can also be used to streamline blunt obstructions (figure 5).

Take advantage of the air moving down near the floor (figure 7). It is better to have a work area blocked by materials stacked to the ceiling with an opening below than to have low stacks 3' (1 m) to 6' (1.8 m) high sitting on the floor.