Filter-bank face area

Find net filter face area and the number of equal filter modules needed to stay at or below a chosen face velocity.

How this calculation works

Enter the design airflow, the maximum face velocity you intend to use and the usable face dimensions of one filter module. The velocity limit must come from the relevant product or design requirement; this calculator does not choose it. Airflow divided by velocity gives the minimum net face area. The module area is width times height, and the required module count is rounded upward to a whole number. Installed usable area is then used to recalculate actual face velocity, making the effect of rounding visible. The method assumes equal modules with uniform flow distribution. Frame obstructions or unusable area should not be included in the input dimensions. Filter efficiency, pressure drop, loading, sealing and physical bank arrangement still need separate manufacturer-based evaluation.

Inputs and units

Design airflow (L/s)
Maximum face velocity (m/s)
Usable module face width (m)
Usable module face height (m)

Method and formula

Arequired = Q/vmax; Amodule = width × height; count = ceil(Arequired/Amodule); actual velocity = Q/(count × Amodule), with Q in m³/s.

Worked example

Example inputs

Design airflow: 2000 L/s
Maximum face velocity: 2 m/s
Usable module face width: 0.6 m
Usable module face height: 0.6 m

Calculation steps

Airflow = 2000 / 1000 = 2 m³/s. Minimum net face area = 2 / 2 = 1 m².
Module area = 0.6 × 0.6 = 0.36 m². Count = ceiling(1 / 0.36) = 3 modules.
Installed usable area = 3 × 0.36 = 1.08 m². Resulting velocity = 2 / 1.08 ≈ 1.851852 m/s.

Example results

Minimum net face area: 1 m²
Whole modules required: 3 modules
Installed usable face area: 1.08 m²
Resulting face velocity: 1.851851852 m/s

Assumptions

Equal modules share flow uniformly; dimensions describe usable face area.

Limitations

Does not predict filter efficiency, pressure drop, loading, seal bypass or bank layout.
Manufacturer velocity and pressure-drop limits still govern.
Preliminary educational check; verify inputs and equipment data before design or operation.

Sources

DOE Fundamentals: Fluid Flow: Continuity and Bernoulli energy balance; centrifugal pumps, equations 3-19 through 3-25; series and parallel piping
TSI: Traversing a Duct, application note TSI-106: Pages 1–3: average local velocities, multiply by area; actual traverses need appropriate measurement layouts