Face Velocity: The Single Number That Sets Core Size and Pressure Drop

Definition

Face velocity is the approach speed of air entering the core face:

face_velocity = volumetric_flow / core_face_area

It is measured in metres per second (m/s).

Typical range

For HVAC air-to-air cores, face velocity usually sits between 1.5 and 3.5 m/s. Lower is gentler on the core and the fan; higher packs more flow into a smaller core.

The core-size vs pressure-drop trade-off

Doubling face velocity roughly quadruples the Perte de charge across the core, which raises fan power. But a smaller core is cheaper and fits tighter casings. Selection is a balance: pick the face area that meets effectiveness at an acceptable fan penalty. This is the same lever discussed for les échangeurs à plaques and their pressure-drop budgets.

Frequently asked questions

Is higher face velocity ever good? Only when space is tight and fan energy is cheap; otherwise lower velocity wins on lifecycle cost.

Does face velocity equal duct velocity? Not exactly – it is referenced to the core opening, which may differ from the connecting duct.

Need help specifying the right air-to-air heat recovery for your project? Contact the QIYU engineering team – WhatsApp +86 157 5335 5505, or email kuns913@gmail.com.

Questions fréquemment posées

Questions fréquemment posées

What is face velocity?

Face velocity is the volumetric airflow divided by the frontal area of the core; it is the speed of air entering the exchanger face.

Why does face velocity affect pressure drop?

Pressure drop rises roughly with the square of face velocity, while effectiveness improves only marginally; lowering face velocity with a larger core is the usual way to cut fan energy.