Filter Pressure Drop and Fan-Energy Penalty
Clean and change-out pressure drop by MERV / HEPA class (velocity-scaled, user-overridable cut-sheet defaults), the fan power at each via brake-HP, and the annual fan energy and loading penalty over a clean filter. Per ASHRAE 52.2-2017 and first-principles fan power.
Formula and source
Airflow (CFM) = face area × face velocity. Pressure drop scales ~linearly with face velocity (Darcy regime): dp(V) = dp_ref × V / 300 fpm. Fan power (kW) = (CFM × dp_in_wc / 6356) / fan total efficiency × 0.7457. Average drop over a linear loading cycle = (clean + change-out) / 2; annual fan energy = average-drop kW × runtime; loading penalty = (average − clean) kW × runtime.
ASHRAE 52.2-2017 (Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size) by name; manufacturer published cut sheets for the pressure-drop values.
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