What needs to be clarified
Review inputs, system resistance and the fan operating point, separating catalogue performance from predicted installed airflow.
Materials to prepare
- Calculation with formulas, units and input table
- Duct plan with lengths, transitions, grille and damper
- Fan curve and make-up air information
What to compare
Reconstruct straight-duct and fitting losses, checking units and assumed velocities. Compare the system curve with the fan curve at the selected setting. Include the filter and available make-up air; compare any measured airflow only under the same system configuration.
Possible outcome of the analysis
A checking table and operating-point graph may identify justified corrections; unknown configuration requires a calculation range and specified field airflow measurements.
Limits of the conclusions
A free-air rating does not equal duct airflow. Arithmetic review cannot confirm duct airtightness, filter condition or adequate make-up air.