System Impedance

  • Laminar vs. Turbulent
  • Entrance/Exit losses
  • Velocity Head
  • Filtration
  • Push vs. Pull
  • Fan Obstruction
  • System Resistance/Fan Curve
  • Pressure Drop vs. Horsepower




Calculating Flow Through A Nozzle


Pressure vs. Suction – Advantages and Disadvantages
Pressure

  • Promotes heat transfer but distribution may be poor
  • Air Leakage is outward keeping out dust (if filtered at fan)
  • Fan handles coolest air which is more dense so mass flow is greatest
  • Fan runs cooler- longer life
  • Fan motor heat dissipates into cooling air stream
Suction
  • Air distribution is more even
  • Air Leakage is into enclosure, contaminating with dust
  • Fan sees warmer air, delivering less mass flow due to lower density
  • Higher temperature can reduce fan life
  • Fan motor heat is not dissipated into cooling air stream