Four-zone measured airflow average

Combine four representative equal-area mean velocity readings into an estimated airflow.

How this calculation works

Enter four representative mean velocities for zones of equal cross-sectional area and the total clear area of the section. Averaging the four zone means gives the section estimate because their area weights are equal. Multiply that average by total area to find volume flow, displayed in liters per second. The range relative to the mean describes the spread between the highest and lowest entered zone values; it is not a measurement uncertainty or an acceptance criterion. Each zone mean may require several local readings from an appropriate traverse layout. Four isolated points do not make a standards-compliant traverse. The model assumes forward flow normal to the section and does not correct for swirl, reverse flow or probe alignment. Average velocities rather than Pitot pressure readings before using this aggregation.

Inputs and units

Total clear cross-sectional area (m²)
Equal-area zone 1 mean velocity (m/s)
Equal-area zone 2 mean velocity (m/s)
Equal-area zone 3 mean velocity (m/s)
Equal-area zone 4 mean velocity (m/s)

Method and formula

Mean velocity = (v1+v2+v3+v4)/4; airflow = mean velocity × total area. Convert m³/s to L/s by multiplying by 1000.

Worked example

Example inputs

Total clear cross-sectional area: 0.5 m²
Equal-area zone 1 mean velocity: 3 m/s
Equal-area zone 2 mean velocity: 4 m/s
Equal-area zone 3 mean velocity: 5 m/s
Equal-area zone 4 mean velocity: 4 m/s

Calculation steps

Mean velocity = (3 + 4 + 5 + 4) / 4 = 4 m/s.
Estimated airflow = 4 × 0.5 = 2 m³/s = 2000 L/s.
Range relative to mean = (5 − 3) / 4 × 100 = 50%.

Example results

Mean velocity: 4 m/s
Estimated airflow: 2000 L/s
Range relative to mean: 50 %

Example notes

Four zone means are a coarse aggregation, not a complete standards-compliant traverse.

Assumptions

Each entered value represents the mean of an equal-area zone; flow is forward normal to the section.

Limitations

Four individual points are not a standards-compliant duct traverse. Each zone may require many local measurements.
No reverse flow, swirl, probe alignment or instrument uncertainty correction; average velocities, not pitot pressures.
Preliminary educational check; verify inputs and equipment data before design or operation.

Sources

TSI: Traversing a Duct, application note TSI-106: Pages 1–3: average local velocities, multiply by area; actual traverses need appropriate measurement layouts