Air motion and distribution can be defined as the movement of the correct quantity of air to the right places at the right time.

This concept is the least studied part of a refrigeration system. Here are a few tips for maintaining proper airflow:

  • Sheet metal screws should not be inside a duct because of potential noise and friction problems.
  • All ells should have sufficient radius and size.
  • Any obstruction increases pressure in the duct, which works against air being pushed through.
  • All edges of metal should have a teardrop design.
  • There are three types of fans to remember:

    The propeller fan: If resistance is added, the cfm will be reduced, thereby reducing the air to the propeller. This will cause the air to flow back through the center of the fan, increasing the wattage of the motor.

    The axial fan: This has the same design as the propeller fan. However, the axial fan prevents air from passing on a buildup of air resistance through the center of the fan. This prevents the increase in wattage of the fan motor that occurs in propeller fans.

    The centrifugal fan: This cylindrical, disk-shaped fan has blades running parallel to the axis. On an increase in air resistance, there is no increase in wattage.

    Finally, a rule of thumb:

  • One ton of refrigeration equals 400 cfm of air needed through the evaporator, or 800 cfm through the air condenser, or 3 gpm of water through a water-cooled condenser.
  • Schaub is president of Schaub Consulting, Medford, NJ.

    Publication date: 08/06/2001