Duct Systems II – Capacity & Performance Measurement

Understanding both fan and duct system operating pressures and how they are best controlled is essential to delivering HVAC system rated performance.

Duct aerodynamics and basic concepts of duct design are used to visualize the physics behind air movement and flow.  The relationship that must exist between fan pressures, duct resistance, air terminal device selection and air balancing provides an excellent roadmap for delivering equipment capacity and performance and comfort.

  • Air distribution system categories and basic principles of quality duct design are used to illustrate minimum requirements for air flow and customer comfort.
  • Examples from existing installations are utilized to guide participants in picturing aerodynamic efficiency in duct systems and the opportunities that exists to quickly improve performance.
  • Air terminal register and diffuser air flow patterns are illustrated in detail to visualize their impact on the primary, secondary and total air streams and how those patterns can be used to determine the optimum return air location.
  • Duct system friction losses and dynamic pressure losses are examined to explain their impact on air flow and how losses can be reduced to increase air flow efficiency.
  • Static pressure measurement techniques are illustrated to show differences in unit static, total external static and differential static pressure measurement options, testing locations and diagnostic applications.
  • Pressure measurement location differences for furnaces and air handlers are shown to provide guidance on proper location for air flow and capacity measurement.
  • Velocity pressure measurement is explored thoroughly to demonstrate duct traversing techniques, how to convert pressure readings to velocity (Fpm) and using velocity profile readings to diagnose air flow problems.
  • Duct traversing is also explored to demonstrate how it is used to characterize (i.e. calibrate) flow hood test instruments during air terminal flow measurement.
  • Duct leakage sources and mitigation techniques are highlighted as they apply to improving HVAC system performance.

The process for balancing residential duct system utilizing “percentage balancing” is demonstrated.  An overview of proportional and temperature air balancing is also provided.