Pressure Drop Is Part of the Cost
Every exchanger adds static pressure. The fan must deliver the design airflow at the new total pressure, and fan power rises with both flow and pressure. Ignore this and you can lose a chunk of the recovered energy to the fan.
Typical Ranges
- Plate core: 50-150 Pa per side at design velocity
- Rotary wheel: 100-250 Pa including the wheel and seals
- Heat pipe: 40-120 Pa, usually the lowest
Sizing the Fan
Take the clean-filter pressure drop from the datasheet, add duct and filter losses, then select a fan with adequate static capability and check its efficiency at the operating point.
Trade-off With Effectiveness
Lower face velocity raises effectiveness but enlarges the core and can change pressure drop non-linearly. The optimum is where the value of recovered energy minus extra fan energy is maximised.
Verification
During commissioning, measure actual pressure drop and compare with the design; a large gap signals fouling or a wrong selection.